# Test Prep for AP® Courses

### 6.1 Induced Emf and Magnetic Flux

To produce current with a coil and bar magnet you can

- Move the coil but not the magnet.
- Move the magnet but not the coil.
- Move either the coil or the magnet.
- It is not possible to produce current.

Calculate the magnetic flux for a coil of area 0.2 m^{2} placed at an angle of *θ*=60º (as shown in the figure above) to a magnetic field of strength 1.5 × 10^{-3} T. At what angle will the flux be at its maximum?

### 6.5 Electric Generators

The emf induced in a coil that is rotating in a magnetic field will be at a maximum when

- The magnetic flux is at a maximum.
- The magnetic flux is at a minimum.
- The change in magnetic flux is at a maximum.
- The change in magnetic flux is at a minimum.

A coil with circular cross section and 20 turns is rotating at a rate of 400 rpm between the poles of a magnet. If the magnetic field strength is 0.6 T and peak voltage is 0.2 V, what is the radius of the coil? If the emf of the coil is zero at *t* = 0 s, when will it reach its peak emf?

### 6.7 Transformers

Which of the following statements is true for a step-down transformer? Select *two* answers.

- Primary voltage is higher than secondary voltage.
- Primary voltage is lower than secondary voltage.
- Primary current is higher than secondary current.
- Primary current is lower than secondary current.

An ideal step-up transformer with turn ratio 1:30 is supplied with an input power of 120 W. If the output voltage is 210 V, calculate the output power and input current.

### 6.8 Electrical Safety: Systems and Devices

Which of the following statements is true for an isolation transformer?

- It has more primary turns than secondary turns.
- It has fewer primary turns than secondary turns.
- It has an equal number of primary and secondary turns.
- It can have more, fewer, or an equal number of primary and secondary turns.

Explain the working of a ground fault interrupter (GFI).