AP Physics 2 : Optics

Study concepts, example questions & explanations for AP Physics 2

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Example Questions

Example Question #1 : Index Of Refraction

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

Determine the index of refraction required in the alcohol to have total internal reflection? 

Possible Answers:

Correct answer:

Explanation:

To have total internal reflection, our equation will become:

Example Question #1 : Index Of Refraction

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

Determine the index of refraction of alcohol if the light ray bends to  to the normal. Assume index of refraction of air is 

Possible Answers:

Correct answer:

Explanation:

We can use our knowledge about the indices of refraction to come up with our equation:

, where  is the index of refraction of air and  is the index of refraction for our alcohol. 

Since 

Example Question #1 : Index Of Refraction

Suppose that a ray of light traveling through air strikes a new medium. Upon doing so, the light bends away from the normal. Which of the following could this new medium be?

Possible Answers:

Vacuum

Diamond

Glass

Carbon dioxide

Water

Correct answer:

Vacuum

Explanation:

For this question, we're told that light is passing from air into another medium. In doing so, the light is refracted such that it bends away from the normal. We're asked to identify a possible medium.

The most important thing to understand about refraction is that when light passes into a new medium at an angle with respect to the normal, that light will be refracted, either away from or toward the normal. This is because light will travel through different media at different speeds. The faster light travels, the more it will bend away from the normal.

Generally, the angle at which light is bent can be predicted by Snell's law. In doing so, this equation takes use of the refractive index, a value unique to each medium. The expression for refractive index is as follows.

Where  refers to the refractive index,  refers to the speed of light in a vacuum, and  refers to the speed of light in a given medium.

Since the speed of light is fastest when in a vacuum, the refractive index can never be less than . Only when the light is in a vacuum is the refractive index equal to . In any other medium, the refractive index will be greater than , even if it is slight.

Light will always refract away from the normal when it passes into a medium with a lower refractive index (indicating the light is traveling faster). Starting from air, the only way this can happen is for the new medium to have an index of refraction that is less than air. Of the answer choices shown, the only one that fits that criteria is the vacuum.

Example Question #2 : Index Of Refraction

The speed of light in a vacuum, , is calculated to be . The speed of light in a diamond is calculated to be . What is the refractive index of diamond?

Possible Answers:

Correct answer:

Explanation:

The definition of refractive index of a medium  is the speed of light in a vacuum divided by the speed of light in the medium:

We have values for  and , so we can plug in our numbers into the equation.

Because we're dividing two values with the same units, our answer is unitless. 

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.

Photo 2 1

What type of reflecting or refracting surface is depicted?

Possible Answers:

Diverging mirror

Plane (flat) mirror

Converging mirror

Diverging lens

Converging lens

Correct answer:

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?

Possible Answers:

Correct answer:

Explanation:

Use the formula for focal length.

Solve for focal length by substituting known values.

Example Question #93 : Optics

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.Malus law

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?

Possible Answers:

Correct answer:

Explanation:

Malus law

Using Malus' law.

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

Example Question #1 : 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.Malus law

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?

Possible Answers:

None of these

Correct answer:

Explanation:

Malus law

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 #513 : Ap Physics 2

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.Malus law

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?

Possible Answers:

None of these

Correct answer:

Explanation:

Malus law

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 #6 : 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?

Possible Answers:

None of these

Correct answer:

Explanation:

Malus law

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:

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