### All AP Physics 2 Resources

## Example Questions

### Example Question #4 : Optics

An object tall is from a mirror. If the image distance is from the mirror, what is the image height?

**Possible Answers:**

**Correct answer:**

The Magnification Equation is as follows:

The negative on the last part is very important. If you don't include it (and it's easy to forget), you will get the wrong answer.

We'll use the parts without for our problem. We want , so we just need to multiply both sides by .

Now, we can plug in our numbers.

Therefore, the image height is .

### Example Question #1 : Magnification

You have a concave mirror and a candle. The candle is tall, and the image is tall. What is the the magnification of the mirror?

**Possible Answers:**

**Correct answer:**

The magnification equation is

where is the height of the image, and is the height of the object. We can plug these given values into the equation.

The magnification is a scalar value, so it's unitless. We can verify this by examining what goes into the equation. Both heights have the same units, which cancel, so that leaves us with no units.

### Example Question #2 : Magnification

The image produced by a concave mirror is at , and the magnification is . What is the object distance?

**Possible Answers:**

**Correct answer:**

The equation for magnification is

We're given the image distance and the magnification, so we'd use the second equality.

Now, we can plug in our numbers.

The negative in front of the equation is very important. If you forget it, the answer will be incorrect.

The distance from the mirror to the object is . Note that the object distance is always positive.

### Example Question #3 : Magnification

An object of height object is placed in front of a convex mirror that has a radius of curvature of . Determine the magnification of the image.

**Possible Answers:**

None of these

**Correct answer:**

Using the relationship:

Where:

is the object distance from the mirror

is the image distance from the mirror

is the focal length of the mirror

is the radius of curvature of the mirror

Plugging in values:

Solving for :

Using the equation for magnification:

Where:

is magnification

### Example Question #4 : Magnification

You are passing a ray of light through a thin tank of alcohol to determine properties. Assume that the light ray is not effected by the tank's exterior. You find that if a piece of white paper is put underneath the alcohol tank, there is an image on the metal.

Assuming that the image is the size of and is actually a picture of a tree of size . What can we say about the magnification of this alcohol solution?

**Possible Answers:**

**Correct answer:**

To determine magnification, we simply divide the object length from the image length.

The negative sign is used to designate that the image is real.