Physics Midterm 2

Front 1

C=Q/V

Back 1

capacitance = charge over voltage

Front 2

C=ε₀A/d

Back 2

parallel plate capacitor: capacitance = epsilon naught * Area / distance between the plates

Front 3

E=E(free)/κ

Back 3

Electric field in dielectric = electric field in free space over kappa

Front 4

C=κC₀

Back 4

the capacitance of a capacitor with a dielectric = kappa * the capacitance without dielectric

Front 5

U=1/2Q∆V=1/2Q²/C=1/2C(∆V)²

Back 5

The potential energy of a capacitor = 1/2 * charge * potential difference = 1/2 * charge squared / capacitance = 1/2 * capacitance * potential difference squared

Front 6

I=∆Q/∆t=dq/dt

Back 6

current = change in charge over change in time

Front 7

R=ρL/A

Back 7

resistance = resistivity * length over area

Front 8

∆R = αR₀∆T

Back 8

change in resistance due to temperature change = temperature coefficient of resistivity (alpha) * original resistance * change in temperature

Front 9

j=I/A

Back 9

current density = current over area

Front 10

R(eq)=R₁+R₂

Back 10

In series, equivalent resistance is the sum of the resistances

Front 11

1/R(eq) = 1/R₁ + 1/R₂

Back 11

In parallel, inverse equivalent resistance is the sum of the inverse resistances

Front 12

∆V=IR

Back 12

Ohm's Law: potential difference = current * resistance

Front 13

the sum of emfs and voltage drops of a closed loop is zero

Back 13

Kirchoff's loop rule

Front 14

the total current going into a junction equals the total current going out of the junction

Back 14

Kirchoff's current rule

Front 15

P = εI

Back 15

The power supplied by an emf source is emf * current

Front 16

P = ∆VI = I²R = (∆V)²/R

Back 16

Power dissapaited by a resistor is potential difference times current is current squared times resistance is potential difference squared over resistance

Front 17

τ = RC

Back 17

characteristic time for RC circuit = resistance * capacitance

Front 18

Q(t) = Cε(1-e^(-t/τ))

Back 18

charge on charging capacitor as function of time is capacitance times emf * (1 - e to the negative time over characteristic time)

Front 19

Q(t) = Cεe^(-t/τ)

Back 19

charge on discharging capacitor as function of time is capacitance times emf times e to the negative time over characteristic time

Front 20

F=μ₀/2π*qvI/r

Back 20

Magnetic force on particle moving with speed v due to current in wire is mu naught over two pi times the charge * velocity * current over distance between particle and wire

Front 21

F = qv×B

Back 21

magnetic force on charged moving particle is charge times velocity cross magnetic field

Front 22

F = qE + qv×B

Back 22

Lorentz force: force on charged particle moving with velocity v is charge times electric field plus charge times velocity cross magnetic field

Front 23

dB = μ₀/4π*Ids×r/r³ = μ₀/4π*Ids*sinθ/r²

Back 23

Biot-Savart: dmagnetic field is mu naught over four pi times current times ds cross r over r cubed

Front 24

∫B·ds = μ₀I

Back 24

Ampere's Law: surface integral of magnetic field dot ds = mu naught times current enclosed

Front 25

r = mv/qB

Back 25

radius of circular orbit in magnetic field

Front 26

dF=IdL×B

Back 26

dforce = current times dlength cross magnetic field

Front 27

F/L = μ₀/2π*I₁I₂/r

Back 27

force per unit length on a wire due to another wire = mu naught over 2pi times current in one wire times current in other wire divided by distance between wires

Front 28

μ=IA

Back 28

magnetic moment of current loop = current times area

Front 29

τ = μ×B

Back 29

torque on current loop in magnetic field = magnetic moment cross magnetic field

Front 30

U = -μ·B

Back 30

potential energy of current loop in magnetic field is negative magnetic moment dot magnetic field