1

An electrical generator has a circular coil with turns of wire on it and a radius of . The coil is making revolutions in a minute inside of a magnetic field with a strength of . What is the peak emf generated by this generator?

A.

B.

C.

D.

For a generator, we have the relationship

For a circular coil

So putting it together

So Correct Answer is A !

2

A transformer has a primary coil with turns of wire and a secondary coil with turns of wire. If the primary coil has a current of running through it, what is the current induced in the secondary and is the transformer a step-up or a step-down transformer?

A.	, Step-Down	C.	, Step-Up
B.	, Step-Down	D.	, Step-Up

The Transformer equation is

Now a step-up transformer is when so since

This is a step-down Transformer

So Correct Answer is B !

3

Pictured to the left is a current moving to right as shown. Two loops are placed near the wire. Each has a resistor as shown. If the current, i, increases over time, each loop will have a current induced in it. Which of the choices below provide the proper direction these induced currents will pass through the respective resistors R1 and R2?

A.	R1 goes right to left R2 goes left to right	C.	R1 goes left to right R2 goes right to left
B.	R1 goes left to right R2 goes left to right	D.	R1 goes right to left R2 goes right to left

The magnetic field created by the current going to the right is as shown above. Since the current is increasing the magnetic fields are each increasing in the direction shown. Therefore, the induced magnetic fields must go in the opposite sense to oppose the change in magnetic flux. So in loop 1, the induced field must go into the paper, which means a clockwise current, or in R1, the current must go left to right.

In loop 2 the induced field is out of the paper so the induced current must go counter-clockwise and therefore the current through R2 must go right to left

So Correct Answer is C !

4

A charge q is traveling with a velocity directed to the right as shown above. It enters a magnetic field B that is directed out of the paper as shown. In what direction should an electric field be directed to keep the charge’s velocity going to the right without any change?

A.

Right

B.

Left

C.

Up

D.

Down

Assume the charge is positive, then the magnetic force from , would result in a force pointing down. Therefore, the electric field, which creates a force , so the electric field should be directed up to cancel out the magnetic force and allow the velocity to remain unchanged.

Note: If q were negative, then the magnetic force would point up but since the charge is negative the electric force would now point down, so the electric field should be directed up whether or not the charge is positive or negative.

So the Correct Answer is C !

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This page last updated on October 16, 2020