Electrostatics and Electromagnetism

Question 1

Charge, conductors, charge conservation

Answer 1

Charges are either positive or negative. Zero charge is neutral.
Like charges repel, unlike charges attract.

Charge is quantized, and the unit of charge is the Coulomb.

Conductors are materials in which charges can move freely. Metals are good conductors.

Charge is always conserved. You can’t create or destroy charge, you can only transfer charge from one source to another.

Question 2

Insulators

Answer 2

Insulators are materials in which charges can not move freely. Nonmetals are good insulators.

Question 3

Coulomb’s law

Question 4

Electric Field Lines

Answer 4

Lines that are closer together denote stronger fields than lines that are farther apart.

Question 5

Electric Field Due to Charge Distribution: Dipoles

Question 6

Electric Field Due to Charge Distributions: Same Charges

Question 7

Electric Field of a Capacitor

Question 8

Electric Field for positive Wire

Question 9

Electrostatic Potential for a positive charge

Question 10

Electrostatic Potential for a negative charge

Question 11

Absolute potential (V)

Answer 11

Absolute potential (V) is the amount of energy per charge that something possesses.

V = U/q₀ = kq/r

Question 12

Potential difference (ΔV)

Answer 12

Potential difference (ΔV) is the difference between two potentials.

ΔV = V_B - V_A

Question 13

Equipotential lines

Answer 13

Equipotential lines are places where the potential is the same.

Equipotential lines are always perpendicular to electric field lines.

Question 14

Electric Dipole

Answer 14

dipole = a positive charge and a negative charge separated by some distance.

Question 15

Behavior of an electric dipole in an electric field

Answer 15

A dipole in an electric field will want to align itself with the electric field, such that the positive end of the dipole is in the direction of the electric field.

Question 16

Potential due to Dipole

Answer 16

To calculate the exact potential at a given point, just calculate the individual potential due to the positive charge and the negative charge, then add them together.

Question 17

Electrostatic Induction

Question 18

Gauss’ Law

Answer 18

• ΦE = EA cosθ
  
  • ΦE is electric flux.

E is electric field, A is area that the field goes through, and θ is the angle between the field and the normal of the area.

• ΦE = q/ε0
  
  • For an enclosed surface, the electric flux is equal to q, the charge inside the enclosure, over the permitivity of free space.
  • The net electric flux through any enclosed surface is totally dependent on the charge inside. If there’s no charge inside, then the net electric flux through the enclosure is zero.

Question 19

Faraday Cage

Answer 19

Basically, the electric field inside a closed conducting cage is zero. This is because the charges on the conducting cage will rearrange to cancel out any external field.

Question 20

Definition of the magnetic field B

Answer 20

Magnetic field B exists in a region of space if a moving charge experiences a force due to its motion in that region.

The unit for magnetic field is the Tesla (T) or N·s/m·C

Question 21

Existence and direction of force on charge moving in magnetic field

Question 22

Charge moving in a circle

Answer 22

F = qvB = mv²/r

You are setting the electromagnetic force equal to the centripetal force, which maintains the orbit. Using this equation, you can solve for whatever the question asks you.

Question 23

Current carrying wires

Answer 23

F = qvB sinθ = (it)vB sinθ = (it)(L/t)B sinθ = iLB sinθ

Question 24

Right Hand Rule

Answer 24

Using your right-hand:
point your index finger in the direction of the charge’s velocity, v, (recall conventional current).

Point your middle finger in the direction of the magnetic field, B.

Your thumb now points in the direction of the magnetic force, F^magnetic.

Question 25

Properties of electromagnetic radiation

Answer 25

• radiation velocity equals constant c, in vacuum
  
  • Electromagnetic radiation travels fastest in a vacuum, at a velocity equals c, or 3x10⁸m/s
  • Light slows down when it travels in a medium other than in vacum. n = c/v, where n is the index of refraction for the medium, and v is the speed of light travelling in that medium.
• radiation consists of oscillating electric and magnetic fields that are mutually perpendicular to each other and to the propagation direction