Electrostatics, Electricity, and Magnetism

Question 1

what is the value of the elementary charge? of a proton or electron

Answer 1

e = 1.6 x 10 ^ -19

+ for proton - for electron

Question 2

Coulomb’s law for 2 point charges

Answer 2

F = kQq/r^2

Question 3

Coulomb’s constant

Answer 3

k = 9 x 10 ^9 Nm^2/c^2

Question 4

Electric field strength (E)

Answer 4

E = kQ/r^2

Q=charge producing the field

Question 5

Electric force formula

Answer 5

F = qE

Formula for coulomb’s law = N

Question 6

Electric potential formula for point charges

Answer 6

φ = kQ/r

in V, scalar

Question 7

Change in electric potential

Answer 7

ΔPE = qΔφ = qV

in J

Question 8

work done by an electric field

Answer 8

W = -ΔPE

Question 9

change in kinetic energy for an electric field

Answer 9

ΔKE = -ΔPE

Question 10

current formula

Answer 10

I = Q/t

in A

Question 11

Resistance formula

Answer 11

R = pL/A

Question 12

Ohm’s law

Answer 12

V=IR

Question 13

Resistors in series (and current/voltage)

Answer 13

R = R1 + R2 …

current is constant, voltage adds up

Question 14

Resistors in parallel (and current/voltage)

Answer 14

1/R = 1/R1 + 1/R2 … or R = R1R2/R1+R2

voltage is constant, current in parallel should equal current entering

Question 15

power for circuit

Answer 15

P=IV
P=I^2R
P=V^2/R
note: the ground is at potential 0.

Question 16

root mean square for AC circuits

Answer 16

Vrms = Vmax/√2
Irms = Imax/√2

Question 17

average power for AC circuit

Answer 17

P = (Irms)^2R
P = Irms (Vrms)

Question 18

charge on parallel plate capacitors

Answer 18

Q=CV

Question 19

capacitance formula

Answer 19

C = εA/d

Question 20

capacitance formula with dielectric

Answer 20

Cwith = KCwithout = KεA/d

Question 21

electric potential for parallel plate capacitor

Answer 21

V=Ed

E=V/m or N/C, same thing!

Question 22

stored potential energy in a capacitor

Answer 22

PE = 1/2QV = 1/2CV^2 = 1/2Q^2/C

Question 23

work done by battery to charge a capacitor

Answer 23

W = PE

Question 24

capacitors in series

Answer 24

1/C = 1/C1 + 1/C2… or C=C1C2/C1+C2

charge is the same across capacitors

Question 25

capacitors in parallel

Answer 25

C = C1 + C2 ….

voltage is the same across capacitors

Question 26

magnetic force on a moving charge

Answer 26

Fb = |q| vBsinθ
θ = angle btw v and B

Question 27

B created by a long straight wire

Answer 27

B ~ I/r

Question 28

B created by a solenoid

Answer 28

B ~ IN/L

L = length of solenoid, N = number of coils

Question 29

What is the direction that magnetic field lines for a bar magnet point

Answer 29

North to South

- north pole will want to line up with external magnetic field (south pole opposite)

Question 30

Which end of the battery is positive in a circuit?

Answer 30

the longer one

Question 31

Energy for a circuit

Answer 31

Energy = Power(time)

in J

Question 32

How to find terminal voltage

Answer 32

V = ε - Ir
V = terminal voltage (real voltage when internal resistance is taken into account)
ε = emf (the original voltage)
I = current (total)
r = internal resistance

Question 33

what are the 2 purposes of a capacitor

Answer 33

1) create a uniform electric field (V=Ed)

2) store electric potential energy (PE=1/2QV etc)

Question 34

Force for a capacitor

Answer 34

F=qE

Question 35

Properties of a capacitor when dielectric is added after disconnecting it from battery

Answer 35

C increases always and Q stays the same.

• V d. by K (Q=CV)
• E d. by K (V=Ed)
• PE d. by K (1/2QV)

Question 36

Properties of a capacitor when dielectric is added before disconnecting it from battery

Answer 36

C increases always and Q increases by K.

• V stays the same (Q=CV)
• E stays the same (V=Ed)
• PE increases by K (1/2QV)

Question 37

work done by magnetic force

Answer 37

Magnetic force does no work on the particle because it does not change the speed of the particle, only the direction.