Magnetism

Magnetic Field of a Wire

(m0 x I)/(2pi R)

Magnetic Field of a Closed Loop; Closed Loop with N turns

N (m0 x I)/(2R)

Magnetic Field of a Solenoid

(N x m0 x I)/L

Magnetic Force from Moving Particles

qv x B; qvBsin(x)

Magnetic Force from a Wire

BILsin(x)

Lorentz Force

qE + (qv x B)

Force Between Two Wires

(m0 x I1 x I2 x L) / (2pi R)

Formula for Flux

ABcos(x), where x is the angle to the normal

Lenz’s Law

Change in flux produces an induced magnetic field opposing the direction of change.

Faraday’s Law (for a single loop)

V=-(d Phi)(dt)=-d/dt (ABcos(x))

Magnetic fields separate charges on a moving conductor, building up charge differences (emf).

Right Hand Rule for an electron is…

Right Hand Rule, then flip answer.

Formula for Power in AC

P = Irms x Vrms = (I/ sqrt(2)) x (V/ sqrt(2))

What is the purpose of a transformer?

Seeks to increase or decrease max voltage.

How does a transformer work?

AC induces a magnetic field, which is trapped and equally distributed within the transformer. The uniform change in flux creates voltage in proportion to the amount of coils.

How do capacitors and inductors behave in AC? Explain how.

They both become like resistors.

Inductors are solenoids, so when current flows through them, they create a changing magnetic field, and thus, a self-imposed opposing magnetic field and current, which is resistance.

Capacitors are like resistors because alternating voltage leads to alternating currents, leading to occasional back flow from capacitors.

Capacitive Reactance

1/(2pi x f x C)

Inductive Reactance

(2pi f) x L
L = m0 x m x N² x L’/A (inductance)

L’ = length of solenoid

Ohm’s Law for Capacitive Reactance (Xc) and Inductive Reactance (Xi)

Irms = Vrms / R, R = Xc or R = Xi

Magnetic Dipole Moment

Measure of the strength of a magnetic source; m = NIA; can be used in torque calculations (t = m x B)