# Chapter 20 Exam 1. According to Lenz`s Law, the direction of an

```Name:_________________
AP Physics
date:____
Chapter 20 Exam
1. According to Lenz’s Law, the direction of an induced current in a conductor will be that
which tends to:
a. Enhance the effect which is producing it
b. Oppose the effect that is producing it
c. Produces the greatest voltage
d. Produces the greatest heating effect
2. A DC motor with an internal resistance of 10 Ohms is operating on a 12 V source
produces a back EMF of 9.0 V. What is the operating current through the motor?
3. A uniform magnetic field of 0.50 T passes perpendicularly through the lane of a wire
loop 0.30 square meters in area.
a. What is the magnetic flux through the loop?
b. After 3 minutes (180 seconds), what is the induced EMF?
4. A bar magnet falls through a loop of wire with the South pole entering first. When the
South pole enters the wire, the induced current will be (as viewed from above):
{hint: you might want to sketch this one out}
a. Clockwise
b. Counterclockwise
c. Zero
d. To the right of the loop
e. To the left of the loop
5. A coil of 5 loops has an area of 0.20 square meters. The coil is oriented with its plane
perpendicular to a magnetic field that increases uniformly from 0.01 T to 0.26 T within
0.005 seconds (5 mS). What is the induced EMF in the coil?
Name:_________________
AP Physics
date:____
6. A transformer consists of a 500 turn primary coil and a 2000 turn secondary coil. If the
voltage in the secondary coil is 4.8 V…
a. What is the primary voltage?
b. How much current is coming into the coil if the current leaving is 0.03 A (30 mA)?
```