# AP Physics 2 : Other Optics Principles

## Example Questions

### Example Question #1 : Other Optics Principles

Light rays encounter a mystery optical device, resulting in a new distribution of the light waves as shown. Assume the light travels from right to left.

What type of reflecting or refracting surface is depicted?

Plane (flat) mirror

Diverging lens

Diverging mirror

Converging lens

Converging mirror

Converging lens

Explanation:

In a converging lens, the light waves pass through it and have their angles altered so that they point closer together than they did before they went through the lens. In the picture, the light waves are diverging from a point until they go into the lens, at which point they no longer diverge from each other. Therefore, this is a converging lens. Because the waves are travelling the same direction the whole time, it can't be the converging or diverging mirrors. If the lens were diverging, they'd be more separated. If it were a plane mirror, the waves would get polarized (they'd have the same phase angle).

### Example Question #2 : Other Optics Principles

If a person with near point distance of 20cm observes a fine detailed coin with magnifying glass with an angular magnification of 5, what is the focal length?

Explanation:

Use the formula for focal length.

Solve for focal length by substituting known values.

### Example Question #3 : Other Optics Principles

Malus' law:

Where is the intensity of polarized light that has passed through the polarizer, is the intensity of polarized light before the polarizer, and is the angle between the polarized light and the polarizer.

Unpolarized light passes through a polarizer. It then passes through another at angle  to the first. What percentage of the original intensity was the light coming out of the second polarizer?

Explanation:

Using Malus' law.

Since the initial light is unpolarized, there will be no intensity lost.

### Example Question #4 : Other Optics Principles

Malus' law:

Where is the intensity of polarized light that has passed through the polarizer, is the intensity of polarized light before the polarizer, and is the angle between the polarized light and the polarizer.

Unpolarized light passes through a polarizer. It then passes through another polarizer at angle to the first, and then another at angle  to the second. What percentage of the original intensity was the light coming out of the third polarizer?

None of these

Explanation:

Use Malus' law.

The light's intensity is reduced by the final two polarizers. It is thus necessary to use Malus' law twice.

Where is the initial intensity after the first polarizer.

is the intensity after the second polarizer.

is the intensity after the third polarizer.

is the angle between the first and second polarizers.

is the angle between the second and third polarizers.

Combining equations:

Plug in values:

### Example Question #5 : Other Optics Principles

Malus' law:

Where is the intensity of polarized light that has passed through the polarizer, is the intensity of polarized light before the polarizer, and is the angle between the polarized light and the polarizer.

Unpolarized light passes through a polarizer. It then passes through another polarizer at angle  to the first, and then another at angle  to the second. What percentage of the original intensity was the light coming out of the third polarizer?

None of these

Explanation:

Use Malus' law.

The light's intensity is reduced by the final two polarizers. We will need to use Malus' law twice.

Where is the initial intensity after the first polarizer.

is the intensity after the second polarizer.

is the intensity after the third polarizer.

is the angle between the first and second polarizers.

is the angle between the second and third polarizers.

Combining equations:

Plug in values:

### Example Question #5 : Other Optics Principles

Malus' law:

Where is the intensity of polarized light that has passed through the polarizer, is the intensity of polarized light before the polarizer, and is the angle between the polarized light and the polarizer.

Unpolarized light passes through a polarizer. It then passes through another polarizer at angle  to the first, and then another at angle  to the second. What percentage of the original intensity was the light coming out of the third polarizer?

None of these

Explanation:

Use Malus' law.

The light's intensity is reduced by the final two polarizers. We will need to use Malus' law twice.

Where is the initial intensity after the first polarizer.

is the intensity after the second polarizer.

is the intensity after the third polarizer.

is the angle between the first and second polarizers.

is the angle between the second and third polarizers.

Combine equations:

Plug in values:

### Example Question #7 : Other Optics Principles

Malus' law:

Where is the intensity of polarized light that has passed through the polarizer, is the intensity of polarized light before the polarizer, and is the angle between the polarized light and the polarizer.

Unpolarized light passes through a polarizer. It then passes through another polarizer at angle  to the first, and then another at angle  to the second. What percentage of the original intensity was the light coming out of the second polarizer?

None of these

Explanation:

Use Malus' law.

The light's intensity is reduced by the final two polarizers. We will need to use Malus' law twice.

Where is the initial intensity after the first polarizer.

is the intensity after the second polarizer.

is the intensity after the third polarizer.

is the angle between the first and second polarizers.

is the angle between the second and third polarizers.

Combine equations:

Plug in values:

### Example Question #8 : Other Optics Principles

Malus' law:

Where is the intensity of polarized light that has passed through the polarizer, is the intensity of polarized light before the polarizer, and is the angle between the polarized light and the polarizer.

Unpolarized light passes through a polarizer. It then passes through another polarizer at angle  to the first, and then another at angle  to the second. What percentage of the original intensity was the light coming out of the third polarizer?

None of these

Explanation:

Use Malus' law.

The light's intensity is reduced by the final two polarizers. We will need to use Malus law twice.

Where is the initial intensity after the first polarizer.

is the intensity after the second polarizer.

is the intensity after the third polarizer.

is the angle between the first and second polarizers.

is the angle between the second and third polarizers.

Combine equations:

Plug in values:

### Example Question #6 : Other Optics Principles

You are passing a ray of light through clear alcohol to determine properties. You shine the light ray exactly  to the surface of alcohol.

Suppose that the alcohol surface will completely reflect the incoming light beam like a mirror. At what angle will the angle of reflectance be to the normal of the surface of the alcohol?

Explanation:

Assuming the alcohol works like a perfect mirror, the angle of reflectance will equal the angle of incidence. Therefore, the angle of reflectance will be

### Example Question #7 : Other Optics Principles

The diffraction of waves refers to the

slowing down of one wave in the presence of another

resultant disturbance of two or more waves at every point

spreading of waves from their initial line of travel

phase change of 180 degrees that occurs on reflection of a wave at a fixed end

change in wavelength that occurs when two waves cross one another