AP physics electromagnetism T2 finals

What is the formula of magnetic field inside a solenoid?

Bin = Magnetic field inside the solenoid (T)

μ_0​=4π×10⁻⁷

n or N = number of turns

I = current (A)

l = length of solenoid (m)

How can you increase the magnetic field around a current carrying solenoid?

What is the formula of the magnetic field strength of a current carrying wire?

B = Magnetic field inside the solenoid (T)

μ_0​=4π×10⁻⁷

r = distance of the point from the wire

If you have 2 parallel wires, what’s the force they’re exerting on eachother?

F = force exerted (N)

μ_0​=4π×10⁻⁷

I = current (A)

L = length of wire (m)

d = distance between the two wires

If a current, I through a current carrying wire is directed out of the page, what is the direction of the magnetic field?

CCW

If a current, I through a current carrying wire is directed into the page, what is the direction of the magnetic field?

CW

What is the formula of magnetic flux?

How do we find out the magnitude of ∮B ds of an amperian loop in a current carrying wire?

Add all the currents enclosed.

• If they are INTO the page make sure they are NEGATIVE

• if they are OUT OF the page make sure they are POSITIVE

How does Faraday’s law explain how a current gets induced as the coil and the magnet move?

As the magnet approaches the ring, the magnetic field and flux increases. According to Faraday’s Law, an induced emf and current are produced to induce magnetic field opposite to the original.

IMPORTANT:
Induced current requires induced emf, which occurs by relative velocity where the distance between must change between the loop and the magnetic.

if the velocity of both the coil and the magnet are the same there will be NO induced current

Why does situation 1 have no induced current?

The relative velocity is zero, so the distance between them does not change.

What would happen to the direction of the induced current here (magnetic field is into the page) when you:

• Decrease the area at a constant rate

• Increase the area at a constant rate

• Decrease: the direction of induced current is clockwise.

• Increase: the direction of induced current is counterclockwise.

How to calculate the rate of energy dissipation if the following are given:

• L (m)

• B (T)

• v (m/s)

• R (ohms/ Ω)

1. Find ε_i = BLv

2. Find I_i = ε_i/R

3. Rate of energy dissipation = P = ε_i x I_i

What is the formula of EMF when there is flux, magnetic field and time is present?

Find current from EMF and resistance.

How would increasing the current in a solenoid affect B?

B and I are directly proportional so increasing I also increases B

How would decreasing the diameter of a solenoid affect B?

There is no direct change but decreasing the diameter sometimes increases n, therefore if n increases, B will increase.

How would inserting an iron core into the solenoid affect B?

It will increase the permeability (μ)

How would decreasing the number of turns affect B?

n/N and B are directly proportional which means when we decrease n/N, B would decrease too

What’s the magnetic flux equation of the figure?

Φ = BAsinθ

Φ = B(π r²)sinθ

What is the mag. flux equation of the figure?

Φ = BAcosθ

A of a square = L²

Φ = BL²cosθ

is an X out or into the page?

into

is a DOT out or into the page?

out of

(FRQ 16) what is the biot-savart formula?

In an LC circuit, how do we get Imax?

Imax = Qmax / √LC

In an LC circuit, how do we get L?

L = Q²_max / Ci²_max

What is the circumference of a circle?

2πr

Q17 FRQ: in part a, how do you find I_enclosed?

I_enclosed = IA_loop / A_wire

Q17 FRQ part 1: What is the equation of B when r>R?

in FRQ 19, what is the equation to find current in the RL circuit when the switch is open?

Finish the equation

How do find time constant in an RL circuit?

L/R

in FRQ 19, what is the equation to find current in the RL circuit when the switch is closed?

Q17 FRQ part 1: What is the equation of B when r<R?