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__NOTOC__ | __NOTOC__ | ||
= '''Georgia Tech Student Wiki for Introductory Physics.''' = | = '''Georgia Tech Student Wiki for Introductory Physics.''' = | ||
| Line 16: | Line 17: | ||
* A wiki written for students by a physics expert [http://p3server.pa.msu.edu/coursewiki/doku.php?id=183_notes MSU Physics Wiki] | * A wiki written for students by a physics expert [http://p3server.pa.msu.edu/coursewiki/doku.php?id=183_notes MSU Physics Wiki] | ||
* A wiki book on modern physics [https://en.wikibooks.org/wiki/Modern_Physics Modern Physics Wiki] | * A wiki book on modern physics [https://en.wikibooks.org/wiki/Modern_Physics Modern Physics Wiki] | ||
* A collection of 26 volumes of lecture notes by Prof. Wheeler of Reed College [https://rdc.reed.edu/c/wheeler/home/] | |||
* The MIT open courseware for intro physics [http://ocw.mit.edu/resources/res-8-002-a-wikitextbook-for-introductory-mechanics-fall-2009/index.htm MITOCW Wiki] | * The MIT open courseware for intro physics [http://ocw.mit.edu/resources/res-8-002-a-wikitextbook-for-introductory-mechanics-fall-2009/index.htm MITOCW Wiki] | ||
* An online concept map of intro physics [http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html HyperPhysics] | * An online concept map of intro physics [http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html HyperPhysics] | ||
| Line 29: | Line 31: | ||
* A guide to representing equations in math mode [https://en.wikipedia.org/wiki/Help:Displaying_a_formula Wiki Math Mode] | * A guide to representing equations in math mode [https://en.wikipedia.org/wiki/Help:Displaying_a_formula Wiki Math Mode] | ||
* A page to keep track of all the physics [[Constants]] | * A page to keep track of all the physics [[Constants]] | ||
* A listing of [[Notable Scientist]] with links to their individual pages | * A listing of [[Notable Scientist]] with links to their individual pages | ||
<div style="float:left; width:30%; padding:1%;"> | <div style="float:left; width:30%; padding:1%;"> | ||
==Physics 1== | ==Physics 1== | ||
===Week 1=== | ===Week 1=== | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
==== | ====GlowScript 101==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Python Syntax]] | *[[Python Syntax]] | ||
*[[GlowScript]] | |||
*[[ | |||
</div> | </div> | ||
</div> | </div> | ||
| Line 98: | Line 88: | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Newton's First Law of Motion]] | *[[Newton's First Law of Motion]] | ||
*[[Mass]] | |||
*[[Velocity]] | *[[Velocity]] | ||
*[[ | *[[Speed]] | ||
*[[Speed | *[[Speed vs Velocity]] | ||
*[[Relative Velocity]] | *[[Relative Velocity]] | ||
*[[Derivation of Average Velocity]] | *[[Derivation of Average Velocity]] | ||
| Line 112: | Line 103: | ||
====Momentum and the Momentum Principle==== | ====Momentum and the Momentum Principle==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Momentum Principle]] | *[[Linear Momentum]] | ||
*[[Newton's Second Law: the Momentum Principle]] | |||
*[[Impulse and Momentum]] | |||
*[[Net Force]] | |||
*[[Inertia]] | *[[Inertia]] | ||
*[[Acceleration]] | *[[Acceleration]] | ||
*[[Relativistic Momentum]] | *[[Relativistic Momentum]] | ||
<!-- Kinematics and Projectile Motion relocated to Week 3 per advice of Dr. Greco --> | |||
</div> | </div> | ||
</div> | </div> | ||
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====Iterative Prediction with a Constant Force==== | ====Iterative Prediction with a Constant Force==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Iterative Prediction]] | *[[Iterative Prediction]] | ||
</div> | </div> | ||
</div> | </div> | ||
| Line 140: | Line 127: | ||
====Analytic Prediction with a Constant Force==== | ====Analytic Prediction with a Constant Force==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Analytical Prediction]] | <!-- *[[Analytical Prediction]] Deprecated --> | ||
*[[Kinematics]] | |||
*[[Projectile Motion]] | |||
</div> | </div> | ||
</div> | </div> | ||
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====Iterative Prediction with a Varying Force==== | ====Iterative Prediction with a Varying Force==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[ | *[[Fundamentals of Iterative Prediction with Varying Force]] | ||
*[[Spring_Force]] | |||
*[[ | |||
*[[Simple Harmonic Motion]] | *[[Simple Harmonic Motion]] | ||
<!--*[[Hooke's Law]] folded into simple harmonic motion--> | |||
<!--*[[Spring Force]] folded into simple harmonic motion--> | |||
*[[Iterative Prediction of Spring-Mass System]] | *[[Iterative Prediction of Spring-Mass System]] | ||
*[[Terminal Speed]] | *[[Terminal Speed]] | ||
*[[Predicting Change in multiple dimensions]] | |||
*[[Two Dimensional Harmonic Motion]] | |||
*[[Determinism]] | *[[Determinism]] | ||
</div> | </div> | ||
| Line 162: | Line 154: | ||
====Fundamental Interactions==== | ====Fundamental Interactions==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Gravitational Force]] | *[[Gravitational Force]] | ||
*[[ | *[[Gravitational Force Near Earth]] | ||
*[[ | *[[Gravitational Force in Space and Other Applications]] | ||
*[[3 or More Body Interactions]] | |||
<!--[[Fluid Mechanics]]--> | |||
*[[Electric Force]] | *[[Electric Force]] | ||
*[[Introduction to Magnetic Force]] | |||
*[[Strong and Weak Force]] | |||
*[[Reciprocity]] | *[[Reciprocity]] | ||
*[[Conservation of Momentum]] | |||
</div> | </div> | ||
</div> | </div> | ||
| Line 175: | Line 169: | ||
===Week 5=== | ===Week 5=== | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Properties of Matter==== | ====Properties of Matter==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
| Line 222: | Line 209: | ||
===Week 7=== | ===Week 7=== | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Jeet Bhatkar==== | |||
====Energy Principle==== | ====Energy Principle==== | ||
The Energy Principle is a fundamental concept in physics that describes the relationship between different forms of energy and their conservation within a system. Understanding the Energy Principle is crucial for analyzing the motion and interactions of objects in various physical scenarios. | |||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Kinetic Energy]] | |||
Kinetic energy is the energy an object possesses due to its motion. | |||
*[[Work/Energy]] | |||
Potential energy arises from the position of an object relative to its surroundings. Common forms of potential energy include gravitational potential energy and elastic potential energy. | |||
*[[The Energy Principle]] | *[[The Energy Principle]] | ||
Work and energy are closely related concepts. Work ( | |||
𝑊) done on an object is defined as the force ( | |||
𝐹) applied to the object multiplied by the displacement ( | |||
𝑑) of the object in the direction of the force: | |||
The Energy Principle states that the total mechanical energy of a system remains constant if only conservative forces (forces that depend only on the positions of the objects) are acting on the system. | |||
*[[Conservation of Energy]] | *[[Conservation of Energy]] | ||
The principle of conservation of energy states that the total energy of an isolated system remains constant over time. In other words, energy cannot be created or destroyed, only transformed from one form to another. This principle is a fundamental concept in physics and has wide-ranging applications in mechanics, thermodynamics, and other branches of science. | |||
</div> | </div> | ||
</div> | </div> | ||
| Line 258: | Line 256: | ||
*[[Center of Mass]] | *[[Center of Mass]] | ||
*[[Multi-particle analysis of Momentum]] | *[[Multi-particle analysis of Momentum]] | ||
*[[Potential Energy of a Multiparticle System]] | *[[Potential Energy of a Multiparticle System]] | ||
*[[Work and Energy for an Extended System]] | *[[Work and Energy for an Extended System]] | ||
| Line 278: | Line 275: | ||
*[[Thermal Energy]] | *[[Thermal Energy]] | ||
*[[Specific Heat]] | *[[Specific Heat]] | ||
*[[Calorific Value(Heat of combustion)]] | *[[Calorific Value(Heat of combustion)]] | ||
*[[First Law of Thermodynamics]] | *[[First Law of Thermodynamics]] | ||
*[[Second Law of Thermodynamics and Entropy]] | *[[Second Law of Thermodynamics and Entropy]] | ||
*[[Temperature]] | *[[Temperature]] | ||
*[[Transformation of Energy]] | *[[Transformation of Energy]] | ||
*[[The Maxwell-Boltzmann Distribution]] | *[[The Maxwell-Boltzmann Distribution]] | ||
*[[Air Resistance]] | *[[Air Resistance]] | ||
*[[The Third Law of Thermodynamics]] | |||
</div> | </div> | ||
</div> | </div> | ||
| Line 296: | Line 290: | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Translational, Rotational and Vibrational Energy]] | *[[Translational, Rotational and Vibrational Energy]] | ||
*[[Rolling Motion]] | |||
</div> | </div> | ||
</div> | </div> | ||
| Line 308: | Line 303: | ||
</div> | </div> | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
==== | ====Friction==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Friction]] | *[[Friction]] | ||
*[[Static Friction]] | *[[Static Friction]] | ||
*[[Kinetic Friction]] | |||
</div> | </div> | ||
</div> | </div> | ||
===Week 12=== | ===Week 12=== | ||
<div class="toccolours mw-collapsible mw-collapsed"> | |||
====Conservation of Momentum==== | |||
<div class="mw-collapsible-content"> | |||
*[[Conservation of Momentum]] | |||
</div> | |||
</div> | |||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Collisions==== | ====Collisions==== | ||
| Line 336: | Line 338: | ||
====Rotations==== | ====Rotations==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[ | *[[Rotational Kinematics]] | ||
*[[Eulerian Angles]] | *[[Eulerian Angles]] | ||
</div> | </div> | ||
</div> | </div> | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Angular Momentum==== | ====Angular Momentum==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
| Line 348: | Line 350: | ||
*[[Rotational Angular Momentum]] | *[[Rotational Angular Momentum]] | ||
*[[The Angular Momentum Principle]] | *[[The Angular Momentum Principle]] | ||
*[[Angular Impulse]] | *[[Angular Impulse]] | ||
*[[Predicting the Position of a Rotating System]] | *[[Predicting the Position of a Rotating System]] | ||
*[[The Moments of Inertia]] | *[[The Moments of Inertia]] | ||
*[[Right Hand Rule]] | *[[Right Hand Rule]] | ||
</div> | </div> | ||
| Line 378: | Line 377: | ||
*[[Energy graphs and the Bohr model]] | *[[Energy graphs and the Bohr model]] | ||
*[[Quantized energy levels]] | *[[Quantized energy levels]] | ||
*[[ | *[[Electron transitions]] | ||
*[[Entropy]] | *[[Entropy]] | ||
</div> | </div> | ||
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<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
== Electric force == | |||
'''Jeet Bhatkar – Fall 2025''' | |||
== Big Idea == | |||
Electric force is the interaction between objects that have electric charge. It is: | |||
* '''Long-range''': acts even when charges do not touch | |||
* '''Vector-valued''': has magnitude and direction | |||
* | * '''Superposable''': forces from many charges add as vectors | ||
At the intro level, the electric force between two point charges is described by Coulomb’s law, the electrostatic analog of the gravitational force between masses. | |||
==== | == Key Equations == | ||
'''Coulomb’s Law (magnitude)''' | |||
:[math]\displaystyle{ F = k \dfrac{|q_1 q_2|}{r^2} }[/math] | |||
* [math]\displaystyle{F}[/math] = magnitude of the electric force | |||
* [math]\displaystyle{k \approx 8.99 \times 10^9\ \text{N·m}^2/\text{C}^2}[/math] | |||
* [math]\displaystyle{q_1, q_2}[/math] = charges (C) | |||
* [math]\displaystyle{r}[/math] = separation between the charges (m) | |||
*[[ | |||
*[[ | |||
*[[ | |||
*[[ | |||
'''Coulomb’s Law (vector form)''' | |||
:[math]\displaystyle{ \vec{F}_{2 \leftarrow 1} = k \dfrac{q_1 q_2}{r^2} \,\hat{r}_{2 \leftarrow 1} }[/math] | |||
* [math]\displaystyle{\vec{F}_{2 \leftarrow 1}}[/math] = force on charge 2 due to charge 1 | |||
* [math]\displaystyle{\hat{r}_{2 \leftarrow 1}}[/math] = unit vector from 1 to 2 | |||
*[[ | |||
*[ | |||
'''Relation to Electric Field''' | |||
:[math]\displaystyle{ \vec{F} = q \vec{E} }[/math] | |||
Once you know [math]\displaystyle{\vec{E}}[/math] at a point, you can find the force on any charge [math]\displaystyle{q}[/math] placed there. | |||
== Conceptual Picture == | |||
=== | |||
'''Sign of charges''' | |||
* Like charges (both positive or both negative) → '''repel''' | |||
* Unlike charges (one positive, one negative) → '''attract''' | |||
''' | |||
'''Distance dependence''' | |||
* Force falls off as [math]\displaystyle{1/r^2}[/math], so doubling the distance makes the force 4 times smaller. | |||
'''Superposition principle''' | |||
If there are many charges, the net force on a given charge is the vector sum of the forces from each individual charge: | |||
[math]\displaystyle{ \vec{F}_\text{net} = \sum_i \vec{F}_i }[/math]. | |||
'''Electric vs. gravitational force''' | |||
* Both follow inverse-square laws | |||
* Gravity is always attractive; electric force can be attractive or repulsive | |||
* Electric forces are usually much stronger at the particle scale | |||
== Worked Example 1: Two Point Charges on a Line == | |||
'''Problem.''' | |||
Two charges are placed on the x-axis: | |||
* [math]\displaystyle{q_1 = +3.0\ \mu\text{C}}[/math] at [math]\displaystyle{x = 0.00\ \text{m}}[/math] | |||
* [math]\displaystyle{q_2 = -2.0\ \mu\text{C}}[/math] at [math]\displaystyle{x = 0.40\ \text{m}}[/math] | |||
[[ | What is the magnitude and direction of the force on [math]\displaystyle{q_2}[/math]? | ||
'''Solution (outline).''' | |||
[[ | # Distance between charges: | ||
[math]\displaystyle{ r = 0.40\ \text{m} }[/math]. | |||
# Magnitude using Coulomb’s law: | |||
[math]\displaystyle{ | |||
F = k \dfrac{|q_1 q_2|}{r^2} | |||
= (8.99 \times 10^9)\,\dfrac{(3.0 \times 10^{-6})(2.0 \times 10^{-6})}{(0.40)^2} | |||
}[/math] | |||
# Sign and direction: | |||
* [math]\displaystyle{q_1}[/math] is positive, [math]\displaystyle{q_2}[/math] is negative → force is '''attractive''' | |||
* On [math]\displaystyle{q_2}[/math], the force points toward [math]\displaystyle{q_1}[/math] | |||
* Since [math]\displaystyle{q_1}[/math] is at smaller x, the force on [math]\displaystyle{q_2}[/math] points in the '''−x''' direction | |||
[[ | You can finish by computing the numerical value and writing it as a vector, e.g. [math]\displaystyle{\vec{F}_{2 \leftarrow 1} = -F\,\hat{x}}[/math]. | ||
== Worked Example 2: Superposition with Three Charges == | |||
'''Problem.''' | |||
Three equal charges [math]\displaystyle{q}[/math] are at the corners of an equilateral triangle of side [math]\displaystyle{a}[/math]. What is the net force on one of the charges? | |||
'''Idea (no full algebra).''' | |||
* Each of the other two charges exerts a force of magnitude | |||
[math]\displaystyle{ F = k \dfrac{q^2}{a^2} }[/math] | |||
* The angle between these two forces is [math]\displaystyle{60^\circ}[/math] | |||
* Use vector addition: | |||
* Add components along the symmetry axis | |||
* Perpendicular components cancel by symmetry | |||
This shows how symmetry plus superposition simplify the vector addition. | |||
== Computational Model (GlowScript) == | |||
Below is a simple GlowScript (VPython) model that computes and visualizes the electric force between two point charges in 3D. | |||
You can: | |||
* Paste this into a new GlowScript Trinket (Python / VPython), | |||
* Get the embed code from Trinket, | |||
* Embed that code into this page so it runs directly here. | |||
<syntaxhighlight lang="python"> | |||
from vpython import * | |||
= | # constant | ||
k = 8.99e9 # N·m^2/C^2 | |||
# scene setup | |||
scene.caption = "Drag the red charge to see how the force on the blue charge changes.\n" | |||
to | |||
# charges (positions in meters, charges in coulombs) | |||
q1 = 2e-6 # C (blue, fixed) | |||
q2 = -3e-6 # C (red, movable) | |||
charge1 = sphere(pos=vector(-0.5, 0, 0), radius=0.05, color=color.blue) | |||
charge2 = sphere(pos=vector(0.5, 0, 0), radius=0.05, color=color.red, make_trail=True) | |||
# arrow to show force on q2 due to q1 | |||
F_arrow = arrow(pos=charge2.pos, axis=vector(0.2, 0, 0)) | |||
def electric_force(q1, q2, r1, r2): | |||
r_vec = r2 - r1 | |||
r = mag(r_vec) | |||
( | if r == 0: | ||
return vector(0, 0, 0) | |||
F_mag = k * q1 * q2 / r**2 | |||
return F_mag * norm(r_vec) | |||
dragging = False | |||
def down(): | |||
global dragging | |||
if scene.mouse.pick is charge2: | |||
dragging = True | |||
def up(): | |||
global dragging | |||
dragging = False | |||
scene.bind("mousedown", lambda evt: down()) | |||
scene.bind("mouseup", lambda evt: up()) | |||
while True: | |||
rate(60) | |||
if dragging: | |||
# move the red charge with the mouse in the x-y plane | |||
m = scene.mouse.pos | |||
charge2.pos = vector(m.x, m.y, 0) | |||
F = electric_force(q1, q2, charge1.pos, charge2.pos) | |||
# update arrow to show force on q2 | |||
F_arrow.pos = charge2.pos | |||
# scale arrow length for visibility (purely visual) | |||
F_arrow.axis = F * 1e7 | |||
</syntaxhighlight> | |||
You can extend this model to include more charges or show the net force on a test charge at different locations. | |||
== Common Mistakes and How to Avoid Them == | |||
* '''Forgetting that force is a vector.''' | |||
Always draw a diagram and keep track of directions. Use components in 2D/3D. | |||
* '''Dropping the absolute value in the magnitude formula.''' | |||
[math]\displaystyle{ F = k \dfrac{|q_1 q_2|}{r^2} }[/math] is a positive magnitude. Decide direction separately. | |||
* '''Mixing up [math]\displaystyle{r}[/math] and [math]\displaystyle{r^2}[/math].''' | |||
The force goes like [math]\displaystyle{1/r^2}[/math], not [math]\displaystyle{1/r}[/math]. | |||
* '''Using wrong units.''' | |||
Convert microcoulombs to coulombs, centimeters to meters, etc. | |||
[math]\displaystyle{1\ \mu\text{C} = 1 \times 10^{-6}\ \text{C}}[/math]. | |||
* '''Trying to memorize instead of understand.''' | |||
Focus on inverse-square behavior, sign of charges, and superposition. | |||
== Connections to Other Topics == | |||
* '''Electric Field''' – Electric force per unit charge is the electric field: | |||
[math]\displaystyle{ \vec{E} = \dfrac{\vec{F}}{q} }[/math]. | |||
* '''Potential Energy and Electric Potential''' – Work done by electric forces leads to electric potential energy and voltage. | |||
* '''Lorentz Force''' – The full force on a moving charge also includes magnetic fields: | |||
[math]\displaystyle{ \vec{F} = q(\vec{E} + \vec{v} \times \vec{B}) }[/math]. | |||
This page focuses on the electric part. | |||
== Practice Problems == | |||
You can add your own numerical values and solve them. Consider including full solutions in a collapsible section. | |||
# Two charges of [math]\displaystyle{+2.0\ \mu\text{C}}[/math] and [math]\displaystyle{+5.0\ \mu\text{C}}[/math] are 0.30 m apart. | |||
* (a) Find the magnitude of the force on each charge. | |||
* (b) Is the force attractive or repulsive? Explain. | |||
# A charge [math]\displaystyle{q_1 = +4.0\ \mu\text{C}}[/math] is at the origin and [math]\displaystyle{q_2 = -1.0\ \mu\text{C}}[/math] is at [math]\displaystyle{x = 0.20\ \text{m}}[/math]. | |||
* Find the electric force on [math]\displaystyle{q_1}[/math] (magnitude and direction). | |||
* Verify that Newton’s third law holds (forces are equal and opposite). | |||
# Three equal positive charges are placed at the corners of a square of side [math]\displaystyle{a}[/math]. | |||
* Find the net force on one of the corner charges. | |||
* Use symmetry to simplify the vector addition. | |||
[[ | # A particle with charge [math]\displaystyle{q = -1.6 \times 10^{-19}\ \text{C}}[/math] experiences an electric force of [math]\displaystyle{3.2 \times 10^{-14}\ \text{N}}[/math] in the +y direction. | ||
* (a) What is the electric field at that point (magnitude and direction)? | |||
* (b) If the charge were positive instead, what would the force direction be? | |||
== What to Review Before an Exam == | |||
* Determine force direction from a diagram, not just from algebra | |||
* Practice vector addition of multiple forces | |||
* Do quick estimates: “If I double the distance, what happens to the force?” | |||
* Know the difference between: | |||
* Force between charges (Coulomb’s law) | |||
* Electric field | |||
* Electric potential energy | |||
====Electric field of a point particle==== | |||
<div class="mw-collapsible-content"> | |||
*[[Point Charge]] | |||
</div> | |||
</div> | |||
<div class="toccolours mw-collapsible mw-collapsed"> | |||
[[ | ====Superposition==== | ||
<div class="mw-collapsible-content"> | |||
*[[Superposition Principle]] | |||
*[[Superposition principle]] | |||
</div> | |||
</div> | |||
<div class="toccolours mw-collapsible mw-collapsed"> | |||
=== | ====Dipoles==== | ||
<div class="mw-collapsible-content"> | |||
*[[Electric Dipole]] | |||
*[[Magnetic Dipole]] | |||
</div> | |||
</div> | |||
===Week 2=== | |||
<div class="toccolours mw-collapsible mw-collapsed"> | |||
====Interactions of charged objects==== | |||
<div class="mw-collapsible-content"> | |||
*[[Electric Field]] | |||
*[[Electric Potential]] | |||
*[[Electric Force]] | |||
*[[Lorentz Force]] | |||
</div> | |||
</div> | |||
<div class="toccolours mw-collapsible mw-collapsed"> | |||
====Tape experiments==== | |||
<div class="mw-collapsible-content"> | |||
*[[Polarization]] | |||
*[[Electric Polarization]] | |||
</div> | |||
</div> | |||
[ | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Polarization==== | |||
<div class="mw-collapsible-content"> | |||
*[[Polarization]] | |||
*[[Electric Polarization]] | |||
*[[Polarization of an Atom]] | |||
</div> | |||
</div> | |||
=== | ===Week 3=== | ||
<div class="toccolours mw-collapsible mw-collapsed"> | |||
====Conductors and Insulators==== | |||
<div class="mw-collapsible-content"> | |||
*[[Conductivity and Resistivity]] | |||
*[[Insulators]] | |||
*[[Potential Difference in an Insulator]] | |||
*[[Conductors]] | |||
*[[Polarization of a conductor]] | |||
</div> | |||
</div> | |||
<div class="toccolours mw-collapsible mw-collapsed"> | |||
= | |||
====Charging and Discharging==== | |||
<div class="mw-collapsible-content"> | |||
*[[Charge Transfer]] | |||
*[[Electrostatic Discharge]] | |||
*[[Charged Conductor and Charged Insulator]] | |||
</div> | </div> | ||
</div> | </div> | ||
===Week 4=== | |||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Field of a charged rod==== | |||
<div class="mw-collapsible-content"> | |||
*[[Field of a Charged Rod|Charged Rod]] | |||
== | |||
</div> | </div> | ||
</div> | </div> | ||
| Line 846: | Line 727: | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Potential energy==== | ====Potential energy==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Potential Energy]] | *[[Potential Energy]] | ||
</div> | </div> | ||
</div> | </div> | ||
| Line 916: | Line 790: | ||
</div> | </div> | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Moving charges, electron current, and conventional current==== | ====Moving charges, electron current, and conventional current==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Moving Point Charge]] | *[[Moving Point Charge]] | ||
A moving point charge creates both electric and magnetic fields. As the charge accelerates or changes position, it alters the surrounding electromagnetic field, which can influence other charges nearby. This is the fundamental concept behind electromagnetic radiation and wave propagation. When many charges move collectively—such as electrons in a wire—this flow is referred to as electric current. This perfectly segues us into the next section of this page. | |||
*[[Current]] | *[[Current]] | ||
Current is typically measured in amperes and represents the rate at which charge flows through a surface. Although electrons carry the charge and move from negative to positive, conventional current is defined in the opposite direction: from positive to negative. This convention dates back to early scientific assumptions and remains standard in circuit diagrams and equations today. | |||
</div> | </div> | ||
</div> | </div> | ||
| Line 928: | Line 810: | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Magnetic Field of a Long Straight Wire]] | *[[Magnetic Field of a Long Straight Wire]] | ||
*[[Magnetic Field of a Curved Wire]] | |||
</div> | </div> | ||
</div> | </div> | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Magnetic field of a current-carrying loop==== | ====Magnetic field of a current-carrying loop==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
| Line 962: | Line 846: | ||
===Week 8=== | ===Week 8=== | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Circuitry Basics==== | |||
<div class="mw-collapsible-content"> | |||
*[[Understanding Fundamentals of Current, Voltage, and Resistance]] | |||
</div> | |||
</div> | |||
<div class="toccolours mw-collapsible mw-collapsed"> | |||
====Steady state current==== | ====Steady state current==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
| Line 972: | Line 865: | ||
====Kirchoff's Laws==== | ====Kirchoff's Laws==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[ | *[[Loop Rule]] | ||
*[[Node Rule]] | |||
</div> | </div> | ||
</div> | </div> | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Electric fields and energy in circuits==== | ====Electric fields and energy in circuits==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Electric Potential Difference]] | *[[Electric Potential Difference]] | ||
</div> | </div> | ||
| Line 987: | Line 879: | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Macroscopic analysis of circuits==== | ====Macroscopic analysis of circuits==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
| Line 1,053: | Line 946: | ||
*[[Magnetic Force]] | *[[Magnetic Force]] | ||
*[[Magnetic Torque]] | *[[Magnetic Torque]] | ||
</div> | </div> | ||
====Magnetic force==== | ====Magnetic force==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
| Line 1,187: | Line 1,069: | ||
====Classical Physics==== | ====Classical Physics==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Classical Physics]] | |||
</div> | </div> | ||
</div> | </div> | ||
=== | [[Category:Which Category did you place this in?]] | ||
===Weeks 2 and 3=== | |||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Special Relativity==== | ====Special Relativity and the Lorentz Transformation==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Frame of Reference]] | *[[Frame of Reference]] | ||
*[[Einstein's Theory of Special Relativity]] | *[[Einstein's Theory of Special Relativity]] | ||
*[[Time Dilation]] | *[[Time Dilation]] | ||
*[[Twin Paradox]] | |||
*[[Lorentz Transformations]] | |||
*[[Relativistic Doppler Effect]] | |||
*[[Einstein's Theory of General Relativity]] | *[[Einstein's Theory of General Relativity]] | ||
*[[Albert A. Micheleson & Edward W. Morley]] | *[[Albert A. Micheleson & Edward W. Morley]] | ||
| Line 1,203: | Line 1,092: | ||
</div> | </div> | ||
===Week | ===Week 4=== | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Photons==== | ====Photons and the Photoelectric Effect==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Spontaneous Photon Emission]] | *[[Spontaneous Photon Emission]] | ||
*[[Light Scattering | *[[Light Scattering]] | ||
*[[Lasers]] | *[[Lasers]] | ||
*[[Electronic Energy Levels and Photons]] | *[[Electronic Energy Levels and Photons]] | ||
*[[Quantum Properties of Light]] | *[[Quantum Properties of Light]] | ||
*[[The Photoelectric Effect]] | |||
</div> | </div> | ||
</div> | </div> | ||
=== | ===Weeks 5 and 6=== | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Matter Waves==== | ====Matter Waves and Wave-Particle Duality==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Wave-Particle Duality]] | *[[Wave-Particle Duality]] | ||
*[[Particle in a 1-Dimensional box]] | |||
*[[Heisenberg Uncertainty Principle]] | |||
</div> | </div> | ||
</div> | </div> | ||
===Week | ===Week 7=== | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Wave Mechanics==== | ====Wave Mechanics==== | ||
| Line 1,232: | Line 1,124: | ||
*[[Mechanical Waves]] | *[[Mechanical Waves]] | ||
*[[Transverse and Longitudinal Waves]] | *[[Transverse and Longitudinal Waves]] | ||
*[[Fourier Series and Transform]] | |||
</div> | |||
</div> | |||
===Week 8=== | |||
<div class="toccolours mw-collapsible mw-collapsed"> | |||
====Schrödinger Equation==== | |||
<div class="mw-collapsible-content"> | |||
*[[The Born Rule]] | |||
*[[Solution for a Single Free Particle]] | |||
*[[Solution for a Single Particle in an Infinite Quantum Well - Darin]] | |||
*[[Solution for a Single Particle in a Semi-Infinite Quantum Well]] | |||
*[[Quantum Harmonic Oscillator]] | |||
*[[Solution for Simple Harmonic Oscillator]] | |||
</div> | |||
</div> | |||
===Week 9=== | |||
<div class="toccolours mw-collapsible mw-collapsed"> | |||
====Quantum Mechanics==== | |||
<div class="mw-collapsible-content"> | |||
*[[Quantum Tunneling through Potential Barriers]] | |||
</div> | |||
</div> | |||
<div class="toccolours mw-collapsible mw-collapsed"> | |||
====The Hydrogen Atom==== | |||
<div class="mw-collapsible-content"> | |||
*[[Quantum Theory]] | |||
*[[Atomic Theory]] | |||
</div> | </div> | ||
</div> | </div> | ||
===Week | ===Week 10=== | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Rutherford-Bohr Model==== | ====Rutherford-Bohr Model==== | ||
| Line 1,246: | Line 1,168: | ||
</div> | </div> | ||
===Week | ===Week 11=== | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
==== | ====Many-Electron Atoms==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Quantum Theory]] | *[[Quantum Theory]] | ||
*[[Atomic Theory]] | *[[Atomic Theory]] | ||
*[[Pauli exclusion principle]] | |||
</div> | </div> | ||
</div> | </div> | ||
===Week | ===Week 12=== | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
==== | ====The Nucleus==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[ | *[[Nucleus]] | ||
</div> | </div> | ||
</div> | </div> | ||
===Week | ===Week 13=== | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Molecules==== | ====Molecules==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Molecules]] | |||
*[[Covalent Bonds]] | |||
</div> | </div> | ||
</div> | </div> | ||
===Week | ===Week 14=== | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Statistical Physics==== | ====Statistical Physics==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Application of Statistics in Physics]] | |||
</div> | </div> | ||
</div> | </div> | ||
===Week | ===Week 15=== | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
==== | ====Statistical Physics==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Temperature & Entropy]] | |||
</div> | </div> | ||
</div> | </div> | ||
=== | ===Additional Topics=== | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
==== | ====Thermodynamics==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[ | *[[Maxwell Relations]] | ||
*[[Brownian Motion]] | |||
</div> | </div> | ||
</div> | </div> | ||
<div class="toccolours mw-collapsible mw-collapsed"> | |||
====Nuclear Physics==== | ====Nuclear Physics==== | ||
<div class="mw-collapsible-content"> | <div class="mw-collapsible-content"> | ||
*[[Nuclear Fission]] | *[[Nuclear Fission]] | ||
*[[Nuclear Energy from Fission and Fusion]] | *[[Nuclear Energy from Fission and Fusion]] | ||
*[[Radioactive Decay Processes]] | |||
</div> | </div> | ||
</div> | </div> | ||
<div class="toccolours mw-collapsible mw-collapsed"> | <div class="toccolours mw-collapsible mw-collapsed"> | ||
====Particle Physics==== | ====Particle Physics==== | ||
| Line 1,310: | Line 1,234: | ||
*[[String Theory]] | *[[String Theory]] | ||
</div> | </div> | ||
</div> | |||
<div class="toccolours mw-collapsible mw-collapsed"> | |||
====Solid-State/Condensed Matter Physics==== | |||
<div class="mw-collapsible-content"> | |||
*[[What is Condensed Matter]] | |||
*[[Crystalline Structures]] | |||
*[[Electric-Band Structure]] | |||
</div> | </div> | ||
</div> | </div> | ||
Latest revision as of 23:21, 30 November 2025
Georgia Tech Student Wiki for Introductory Physics.
This resource was created so that students can contribute and curate content to help those with limited or no access to a textbook. When reading this website, please correct any errors you may come across. If you read something that isn't clear, please consider revising it for future students!
Looking to make a contribution?
- Pick one of the topics from intro physics listed below
- Add content to that topic or improve the quality of what is already there.
- Need to make a new topic? Edit this page and add it to the list under the appropriate category. Then copy and paste the default Template into your new page and start editing.
Please remember that this is not a textbook and you are not limited to expressing your ideas with only text and equations. Whenever possible embed: pictures, videos, diagrams, simulations, computational models (e.g. Glowscript), and whatever content you think makes learning physics easier for other students.
Source Material
All of the content added to this resource must be in the public domain or similar free resource. If you are unsure about a source, contact the original author for permission. That said, there is a surprisingly large amount of introductory physics content scattered across the web. Here is an incomplete list of intro physics resources (please update as needed).
- A physics resource written by experts for an expert audience Physics Portal
- A wiki written for students by a physics expert MSU Physics Wiki
- A wiki book on modern physics Modern Physics Wiki
- A collection of 26 volumes of lecture notes by Prof. Wheeler of Reed College [1]
- The MIT open courseware for intro physics MITOCW Wiki
- An online concept map of intro physics HyperPhysics
- Interactive physics simulations PhET
- OpenStax intro physics textbooks: Vol1, Vol2, Vol3
- The Open Source Physics project is a collection of online physics resources OSP
- A resource guide compiled by the AAPT for educators ComPADRE
- The Feynman lectures on physics are free to read Feynman
- Final Study Guide for Modern Physics II created by a lab TA Modern Physics II Final Study Guide
Resources
- Commonly used wiki commands Wiki Cheatsheet
- A guide to representing equations in math mode Wiki Math Mode
- A page to keep track of all the physics Constants
- A listing of Notable Scientist with links to their individual pages
Physics 1
Week 1
GlowScript 101
VPython
Vectors and Units
Interactions
Velocity and Momentum
Week 2
Momentum and the Momentum Principle
Iterative Prediction with a Constant Force
Week 3
Analytic Prediction with a Constant Force
Iterative Prediction with a Varying Force
Week 4
Fundamental Interactions
Week 5
Properties of Matter
Week 6
Identifying Forces
Curving Motion
Week 7
Jeet Bhatkar
Energy Principle
The Energy Principle is a fundamental concept in physics that describes the relationship between different forms of energy and their conservation within a system. Understanding the Energy Principle is crucial for analyzing the motion and interactions of objects in various physical scenarios.
Week 8
Work by Non-Constant Forces
Potential Energy
Week 9
Multiparticle Systems
Week 10
Choice of System
Thermal Energy, Dissipation, and Transfer of Energy
Rotational and Vibrational Energy
Week 11
Different Models of a System
Friction
Week 12
Conservation of Momentum
Collisions
Week 13
Rotations
Angular Momentum
Week 14
Analyzing Motion with and without Torque
Week 15
Introduction to Quantum Concepts
Physics 2
Week 1
3D Vectors
Electric field
Electric force
Jeet Bhatkar – Fall 2025
Big Idea
Electric force is the interaction between objects that have electric charge. It is:
- Long-range: acts even when charges do not touch
- Vector-valued: has magnitude and direction
- Superposable: forces from many charges add as vectors
At the intro level, the electric force between two point charges is described by Coulomb’s law, the electrostatic analog of the gravitational force between masses.
Key Equations
Coulomb’s Law (magnitude)
- [math]\displaystyle{ F = k \dfrac{|q_1 q_2|}{r^2} }[/math]
- [math]\displaystyle{F}[/math] = magnitude of the electric force
- [math]\displaystyle{k \approx 8.99 \times 10^9\ \text{N·m}^2/\text{C}^2}[/math]
- [math]\displaystyle{q_1, q_2}[/math] = charges (C)
- [math]\displaystyle{r}[/math] = separation between the charges (m)
Coulomb’s Law (vector form)
- [math]\displaystyle{ \vec{F}_{2 \leftarrow 1} = k \dfrac{q_1 q_2}{r^2} \,\hat{r}_{2 \leftarrow 1} }[/math]
- [math]\displaystyle{\vec{F}_{2 \leftarrow 1}}[/math] = force on charge 2 due to charge 1
- [math]\displaystyle{\hat{r}_{2 \leftarrow 1}}[/math] = unit vector from 1 to 2
Relation to Electric Field
- [math]\displaystyle{ \vec{F} = q \vec{E} }[/math]
Once you know [math]\displaystyle{\vec{E}}[/math] at a point, you can find the force on any charge [math]\displaystyle{q}[/math] placed there.
Conceptual Picture
Sign of charges
- Like charges (both positive or both negative) → repel
- Unlike charges (one positive, one negative) → attract
Distance dependence
- Force falls off as [math]\displaystyle{1/r^2}[/math], so doubling the distance makes the force 4 times smaller.
Superposition principle If there are many charges, the net force on a given charge is the vector sum of the forces from each individual charge: [math]\displaystyle{ \vec{F}_\text{net} = \sum_i \vec{F}_i }[/math].
Electric vs. gravitational force
- Both follow inverse-square laws
- Gravity is always attractive; electric force can be attractive or repulsive
- Electric forces are usually much stronger at the particle scale
Worked Example 1: Two Point Charges on a Line
Problem. Two charges are placed on the x-axis:
- [math]\displaystyle{q_1 = +3.0\ \mu\text{C}}[/math] at [math]\displaystyle{x = 0.00\ \text{m}}[/math]
- [math]\displaystyle{q_2 = -2.0\ \mu\text{C}}[/math] at [math]\displaystyle{x = 0.40\ \text{m}}[/math]
What is the magnitude and direction of the force on [math]\displaystyle{q_2}[/math]?
Solution (outline).
- Distance between charges:
[math]\displaystyle{ r = 0.40\ \text{m} }[/math].
- Magnitude using Coulomb’s law:
[math]\displaystyle{ F = k \dfrac{|q_1 q_2|}{r^2} = (8.99 \times 10^9)\,\dfrac{(3.0 \times 10^{-6})(2.0 \times 10^{-6})}{(0.40)^2} }[/math]
- Sign and direction:
- [math]\displaystyle{q_1}[/math] is positive, [math]\displaystyle{q_2}[/math] is negative → force is attractive
- On [math]\displaystyle{q_2}[/math], the force points toward [math]\displaystyle{q_1}[/math]
- Since [math]\displaystyle{q_1}[/math] is at smaller x, the force on [math]\displaystyle{q_2}[/math] points in the −x direction
You can finish by computing the numerical value and writing it as a vector, e.g. [math]\displaystyle{\vec{F}_{2 \leftarrow 1} = -F\,\hat{x}}[/math].
Worked Example 2: Superposition with Three Charges
Problem. Three equal charges [math]\displaystyle{q}[/math] are at the corners of an equilateral triangle of side [math]\displaystyle{a}[/math]. What is the net force on one of the charges?
Idea (no full algebra).
- Each of the other two charges exerts a force of magnitude
[math]\displaystyle{ F = k \dfrac{q^2}{a^2} }[/math]
- The angle between these two forces is [math]\displaystyle{60^\circ}[/math]
- Use vector addition:
* Add components along the symmetry axis * Perpendicular components cancel by symmetry
This shows how symmetry plus superposition simplify the vector addition.
Computational Model (GlowScript)
Below is a simple GlowScript (VPython) model that computes and visualizes the electric force between two point charges in 3D.
You can:
- Paste this into a new GlowScript Trinket (Python / VPython),
- Get the embed code from Trinket,
- Embed that code into this page so it runs directly here.
<syntaxhighlight lang="python"> from vpython import *
- constant
k = 8.99e9 # N·m^2/C^2
- scene setup
scene.caption = "Drag the red charge to see how the force on the blue charge changes.\n"
- charges (positions in meters, charges in coulombs)
q1 = 2e-6 # C (blue, fixed) q2 = -3e-6 # C (red, movable)
charge1 = sphere(pos=vector(-0.5, 0, 0), radius=0.05, color=color.blue) charge2 = sphere(pos=vector(0.5, 0, 0), radius=0.05, color=color.red, make_trail=True)
- arrow to show force on q2 due to q1
F_arrow = arrow(pos=charge2.pos, axis=vector(0.2, 0, 0))
def electric_force(q1, q2, r1, r2):
r_vec = r2 - r1
r = mag(r_vec)
if r == 0:
return vector(0, 0, 0)
F_mag = k * q1 * q2 / r**2
return F_mag * norm(r_vec)
dragging = False
def down():
global dragging
if scene.mouse.pick is charge2:
dragging = True
def up():
global dragging dragging = False
scene.bind("mousedown", lambda evt: down()) scene.bind("mouseup", lambda evt: up())
while True:
rate(60)
if dragging:
# move the red charge with the mouse in the x-y plane
m = scene.mouse.pos
charge2.pos = vector(m.x, m.y, 0)
F = electric_force(q1, q2, charge1.pos, charge2.pos)
# update arrow to show force on q2 F_arrow.pos = charge2.pos # scale arrow length for visibility (purely visual) F_arrow.axis = F * 1e7
</syntaxhighlight>
You can extend this model to include more charges or show the net force on a test charge at different locations.
Common Mistakes and How to Avoid Them
- Forgetting that force is a vector.
Always draw a diagram and keep track of directions. Use components in 2D/3D.
- Dropping the absolute value in the magnitude formula.
[math]\displaystyle{ F = k \dfrac{|q_1 q_2|}{r^2} }[/math] is a positive magnitude. Decide direction separately.
- Mixing up [math]\displaystyle{r}[/math] and [math]\displaystyle{r^2}[/math].
The force goes like [math]\displaystyle{1/r^2}[/math], not [math]\displaystyle{1/r}[/math].
- Using wrong units.
Convert microcoulombs to coulombs, centimeters to meters, etc.
[math]\displaystyle{1\ \mu\text{C} = 1 \times 10^{-6}\ \text{C}}[/math].
- Trying to memorize instead of understand.
Focus on inverse-square behavior, sign of charges, and superposition.
Connections to Other Topics
- Electric Field – Electric force per unit charge is the electric field:
[math]\displaystyle{ \vec{E} = \dfrac{\vec{F}}{q} }[/math].
- Potential Energy and Electric Potential – Work done by electric forces leads to electric potential energy and voltage.
- Lorentz Force – The full force on a moving charge also includes magnetic fields:
[math]\displaystyle{ \vec{F} = q(\vec{E} + \vec{v} \times \vec{B}) }[/math].
This page focuses on the electric part.
Practice Problems
You can add your own numerical values and solve them. Consider including full solutions in a collapsible section.
- Two charges of [math]\displaystyle{+2.0\ \mu\text{C}}[/math] and [math]\displaystyle{+5.0\ \mu\text{C}}[/math] are 0.30 m apart.
* (a) Find the magnitude of the force on each charge. * (b) Is the force attractive or repulsive? Explain.
- A charge [math]\displaystyle{q_1 = +4.0\ \mu\text{C}}[/math] is at the origin and [math]\displaystyle{q_2 = -1.0\ \mu\text{C}}[/math] is at [math]\displaystyle{x = 0.20\ \text{m}}[/math].
* Find the electric force on [math]\displaystyle{q_1}[/math] (magnitude and direction).
* Verify that Newton’s third law holds (forces are equal and opposite).
- Three equal positive charges are placed at the corners of a square of side [math]\displaystyle{a}[/math].
* Find the net force on one of the corner charges. * Use symmetry to simplify the vector addition.
- A particle with charge [math]\displaystyle{q = -1.6 \times 10^{-19}\ \text{C}}[/math] experiences an electric force of [math]\displaystyle{3.2 \times 10^{-14}\ \text{N}}[/math] in the +y direction.
* (a) What is the electric field at that point (magnitude and direction)? * (b) If the charge were positive instead, what would the force direction be?
What to Review Before an Exam
- Determine force direction from a diagram, not just from algebra
- Practice vector addition of multiple forces
- Do quick estimates: “If I double the distance, what happens to the force?”
- Know the difference between:
* Force between charges (Coulomb’s law) * Electric field * Electric potential energy