AP Physics 2 : AP Physics 2

Study concepts, example questions & explanations for AP Physics 2

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Example Questions

Example Question #201 : Ap Physics 2

e = 1.60 \times 10^{-19}

k = 8.99 \times 10^{9}

 

How many electrons would it require to generate a 5 N attractive force on a +3 µC charge from 0.1 m away.

Possible Answers:

2.3 x 10–13 electrons

1.15 x 1013 electrons

1.15 x 10–14 electrons

 

0.68 x 1014 electrons

Correct answer:

1.15 x 1013 electrons

Explanation:

To find the answer we must first solve for q, using Coulomb's Law. Then after finding q = 1.85 x 10–6 C, we must divide by 1.6 x 10–19 C to get the amount of electrons required to make such a charge.

Example Question #1 : Waves

Which of the following electromagnetic waves has the highest frequency?

Possible Answers:

Gamma 

Visible light

Microwave

Infrared

Radio

Correct answer:

Gamma 

Explanation:

The frequency of a wave is directly related to the energy in the wave. The most energetic waves in the electromagnetic spectrum are gamma rays. Gamma rays are typically released from quasars, ultra-dense dying stars, and from atomic bomb blasts, which gives you the scope of the amount of energy involved with gamma rays.

Example Question #2 : Waves

For open pipes, the formula for wave patterns at any given time can be given by a Fourier Sine Series which is given as the infinite sum:

 when  is an integer, and  is the length of the pipe. Each individual value of  is called a harmonic. 

What is the angular frequency of the second harmonic? 

Possible Answers:

Correct answer:

Explanation:

Frequency, when given an equation in sine or cosine notation, is the value inside the parenthesis. For the second harmonic , the frequency is:

Example Question #2 : Waves

Equation of sound wave 1:

Equation of sound wave 2:

Determine at what time there will be complete constructive interference between the two if:

Possible Answers:

None of these

Correct answer:

Explanation:

The will be destructive interference when 

Using

Plugging in values:

Example Question #2 : Waves

Wave interference is __________ when the amplitudes of the waves add together to make a larger wave overall, while it is __________ when the amplitudes of the waves work against one another to make a smaller wave overall.

Possible Answers:

destructive . . . constructive

refractive . . . constructive

constructive . . . destructive

diffusive . . . destructive

refractive . . . detractive

Correct answer:

constructive . . . destructive

Explanation:

When waves add together and make a larger wave, think of them as constructing a big wave. On the other hand, waves that make a smaller wave are said to be destructive because they are "destructing" each other and making a smaller wave, or no wave at all.

Example Question #1 : Waves

When light __________ interferes, the result is __________ light overall, and when light __________ interferes, the result is __________ light overall.

Possible Answers:

destructively . . . brighter . . . contsructively . . . less bright

None of these

subtractively . . . brighter . . . additionally . . . less bright

additionally . . . brighter . . . subtractively . . . less bright

constructively . . . brighter . . . destructively . . . less bright

Correct answer:

constructively . . . brighter . . . destructively . . . less bright

Explanation:

Because light has properties of waves, it can have interference. When two crests of the wave meet, this is known as constructive interference, and results in the two crests adding, meaning the light gets brighter. When a crest and a trough meet, this is known as destructive interference, and results in the two partially or completely cancelling each other out, making the observed light less bright.

Example Question #1 : Waves

Suppose that monochromatic light is passed through a sheet of glass from air. As it travels through the glass, it is refracted. Which of the following parameters of the light does not remain the same?

Possible Answers:

All of these parameters stay the same

Wavelength

Energy

Frequency

Period

Correct answer:

Wavelength

Explanation:

This question is describing a scenario in which a ray of monochromatic light is being refracted by passing from air into glass. We're then asked to determine which parameter of the light does not change.

First of all, let's review what refraction is. Refraction is an event that happens whenever light passes from one medium into another medium. In doing so, the ray bends. This bending of light is due to the fact that the speed of light changes depending on the medium in which it is traveling.

As the light crosses from the air and into the glass, its speed is slowed down. This is because glass is denser than air. Also, since the speed of light is a function of both wavelength and frequency, then one or both of these variables must change. The frequency remains unchanged while the wavelength becomes altered. One way to think about this is by applying conservation of energy. If the frequency changed, then the energy of the light would also change. However, the energy of the light remains unchanged during refraction. Thus, only the wavelength and the speed change.

Since frequency remains the same, we also know that the period will stay the same, since period is just the inverse of frequency. Also, as was mentioned above, energy will not change because energy is a function of frequency.

Example Question #1 : Doppler Effect

A bat is flying towards a stationary wall at a constant speed of . The bat emits a sound of  towards the wall, which is then reflected back at the bat. If the speed of sound in air is , what is the frequency of sound that the bat experiences?

Possible Answers:

Correct answer:

Explanation:

To answer this question, it's imperative to realize that we'll need to use the equation for the doppler effect. First, we'll need to calculate the frequency of the sound that reaches the wall. Then, we'll have to calculate the frequency of the reflected wave that reaches the bat.

The doppler effect equation is:

In the first case, we'll consider the frequency received by the wall. The bat is the source in this scenario, which is moving, while the wall is the stationary observer. Therefore, the  term in the above equation is 0. Moreover, since the bat is moving towards the wall, we should expect the frequency received by the wall to be larger than the original frequency. Hence, we will need to subtract the speed of the source in the denominator, since that will result in the expected increase in observed frequency.

Now that we have the frequency relfected from the wall, we can calculate the frequency that the bat will experience. In this scenario, the wall is now the source. But because it isn't moving, we can say that the  term in the doppler equation is 0. Likewise, the bat is now the observer in this case and is still moving at a speed of . Also, because the bat is moving towards the source, then conceptually we should expect the bat to observe a frequency that is greater than that reflected by the wall. To ensure this, we will need to add the  term in the numerator of the doppler equation.

Example Question #2 : Doppler Effect

If a music box produces a tone of  as a boy is running towards the music box at , what is the frequency the boy hears?

Possible Answers:

Correct answer:

Explanation:

The formula for the Doppler effect of the moving observer is:

Since the boy is approaching, the positive sign will be used. The velocity of sound is . Substitute the knowns into the formula.

Example Question #1 : Doppler Effect

Suppose a car moves at  and produces a  honk. A runner running at  approaches the car. About what frequency does the runner hear?

Possible Answers:

Correct answer:

Explanation:

This scenario deals with both a moving source and a moving observer.

Write the correct Doppler effect formula for this case.

Since the observer and the source are both approaching, the numerator will have a positive sign and the denominator will have a negative sign. The speed of sound is . Substitute all the knowns and find the frequency.

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