AP Physics 1 : AP Physics 1

Study concepts, example questions & explanations for AP Physics 1

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Example Questions

Example Question #1 : Electricity And Waves

An open pipe (open at both ends) has a fundamental frequency of 600Hz. How long is the pipe?

Possible Answers:

Correct answer:

Explanation:

An open pipe can be modeled by the following equation: 

Rearrange the equation to solve for  then plug in given values and solve.



Example Question #1 : Sound Waves

A student at a concert notices that a balloon near the large speakers moving slightly towards, then away from the speaker during the low-frequency passages. The student explains this phenomenon by noting that the waves of sound in air are __________ waves.

Possible Answers:

electromagnetic

longitudinal

latitudinal

torsional

transverse

Correct answer:

longitudinal

Explanation:

Sound is a longitudinal, or compression wave. A region of slightly more compressed air is followed by a region of slightly less compressed air (called a rarefaction). When the compressed air is behind the balloon, it pushes it forward, and when it is in front of the balloon, it pushes it back. This only works if the frequency is low, because the waves are long enough so that the balloon can react to them.

Example Question #7 : Sound Waves

Consider a 37cm long harp string with a fundamental frequency of 440Hz.

Calculate the speed of the standing wave created by plucking this string.

Possible Answers:

Correct answer:

Explanation:

Use the following equation to find the velocity of the wave, using its fundamental frequency and the length:

Example Question #11 : Sound Waves

Consider a 37cm long harp string with a fundamental frequency of 440Hz.

Suppose the string is pressed down in such a way that only a 10cm length of string vibrates. What is the speed of the wave produced when the string is plucked in terms of  the speed of the wave when all 37cm of the string vibrate?

Possible Answers:

Correct answer:

Explanation:

The speed of a wave is a property of the medium, it is not affected by the length of the string. The frequency may change, but the speed remains constant. There is no change in the speed.

Example Question #1161 : Ap Physics 1

Consider a 37cm long harp string with a fundamental frequency of 440Hz.

If only half of the string is allowed to vibrate, what frequency will be heard?

Possible Answers:

Correct answer:

Explanation:

Since the speed of the wave does not change based on the length of the string and we know it has a fundamental frequency of 440Hz, a string of half the length will vibrate at twice the frequency, 880Hz. This makes sense as it will sound higher in pitch. You can try this with a rubber band on a shoebox. Plucking it while placing your finger halfway along the band will result in a higher pitched sound.

Example Question #1162 : Ap Physics 1

Consider a 37cm long harp string with a fundamental frequency of 440Hz.

What is the wavelength of the second harmonic of the string?

Possible Answers:

Correct answer:

Explanation:

The wavelength of the second harmonic of a standing wave on a string is just the length of the string. For the second harmonic, an entire cycle occurs on the length of the string. Therefore, the wavelength of the second harmonic for this string is 37cm or 0.37m. The wavelength for the first harmonic, or fundamental, is twice the length of the string, as this is when one half a cycle occurs over the length of the string.

Example Question #14 : Electricity And Waves

If the first harmonic of a string has frequency , what is the frequency of the  harmonic of that string in terms of ?

Possible Answers:

Correct answer:

Explanation:

Harmonics describe the relationship between wavelengths and frequency on a string. A given string will have a wave speed associated with it. Given this wave speed, the harmonics are the frequencies at which half-wavelengths occur along the length of the string. For instance, the first harmonic is the frequency at which a half-wavelength occurs over the string. The second harmonic completes one wave over the string. The string is 1.5 times the wavelength of the third harmonic and so on. Therefore, the  harmonic has a frequency of .

Example Question #11 : Sound Waves

Given that 20kJ of energy are hitting a window pane over a period of 5s with dimensions 2.5m by 4m, what is the sound level in decibels? 

Possible Answers:

Correct answer:

Explanation:

The formula for intensity,  is:

Where  is power in watts and  is the surface area. The surface area  in our case is: 

The power  can be given as  or in our case:

Solve for intensity.

The formula for sound level  is:

, where  is the intensity and  is the threshold of hearing, which is 

Example Question #14 : Sound Waves

At a distance of  from a fan exerting  of mechanical energy, estimate the sound level if the threshold of hearing is 

Possible Answers:

Correct answer:

Explanation:

First we need to solve for intensity , given by: 

, where  is power,  is the distance from the source of the sound. 

In our case,  and , therefore

To solve for sound level , we do

, where is the intensity and  is the threshold of hearing. 

In this problem, 

, and 

 

 

Example Question #17 : Electricity And Waves

By what factor will the sound level in decibels change if the intensity is increased by a factor of 

Possible Answers:

Sound level will change by a factor of 

Sound level will change by a factor of 

Sound level will change by a factor of 

Sound level will change by a factor of 

Correct answer:

Sound level will change by a factor of 

Explanation:

Recall that the formula for sound level  given in decibels is given by:

, where  is the intensity and  is the threshold of hearing. 

Sound level is proportional to intensity by:

If the intensity is increased by a factor of , sound level would increase by a factor of 

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