# Physical Science Module 14 Study Guide Questions and Short Answers

Transverse wave
A wave with a direction of propagation that is perpendicular to its direction of oscillation.

Longitudinal wave
A wave with a direction of propagation that is parallel to its direction of oscillation.

Supersonic speed
Any speed that is faster than the speed of sound in the substance of interest.

Sonic boom
The sound produced as a result of an object traveling at or above Mach 1.

Pitch
An indication of how high or low a sound is, which is primarily determined by the frequency of the sound wave.

In designing a car’s horn, the engineers test the sound of the horn and decide that its pitch is too low. To adjust the horn, should the engineers change the electronics so as to produce sound waves with longer or shorter wavelengths?
Shorter.

A sound wave is traveling through the air with a temperature of 30 °C. What is the speed of the sound wave?
349.5 m/sec.

If the sound wave in problem #3 has a wavelength of 0.5 meters, what is its frequency.
699 Hz.

A sound wave has a speed of 345m/sec and a wavelength of 500 meters. Is this wave infrasonic, sonic, or ultrasonic?
Infrasonic.

A physicist takes an alarm clock and puts it in an airtight chamber. When the chamber is sealed but still full of air, the physicist can still hear the alarm despite the fact that he is outside of the chamber. If the physicist then uses a vacuum pump to evacuate essentially all the air out of the chamber, will the physicist still be able to hear the alarm? Why or why not?
No. Because without air, the sound waves from the alarm have nothing through which to travel. Thus, they cannot make waves. As a result, there is no sound.

Are sound waves transverse waves or longitudinal waves?
Longitudinal.

You are watching the lightning from a thunderstorm. You suddenly see a flash of lightning, and 2.3 seconds later, you hear the thunder. How far away from you did the lightning strike? (The temperature at the time is 13 °C.)
780.39 m.

Sound waves are traveling through the air and suddenly run into a wall. As the sound waves travel through the wall, do they travel faster, slower, or at the same speed as when they were traveling in the air?
Faster.

In the situation described above, what happens to the amplitude of the wave? Is the amplitude of the wave smaller, larger, or the same as the amplitude before the wave hit the wall?
Smaller.

A jet aircraft is traveling at Mach 2.5 through air at 1 °C. What is the jet’s speed in m/sec?
830.25 m/sec.

A jet is traveling through air at 464.1 m/sec. If the air has a temperature of 0 °C, at what Mach number is the jet flying?
Mach 1.4.

Why do jets travel at speeds of Mach 1 or higher only in sparsely populated regions?
Because the sound waves that come from the sonic boom are strong enough to cause damage to people’s hearing, as well as buildings.

A guitar player is plucking on a string. If he takes his finger and pinches the string to the neck of the guitar so as to shorten the length of the string, will the pitch of the sound emitted increase, decrease, or stay the same?
Increase.

You hear two musical notes. They both have the same pitch, but the first is louder than the second. If you compare the sound waves of each sound what aspect(s) of the wave (wavelength, frequency, speed, amplitude) would be the same? What aspect(s) would be different?
The wavelength, frequency, and speed will be the same. The amplitude of the waves will be different.

The horn on your neighbor’s car is stuck, so it is constantly blaring. You watch your neighbor get into the car and drive away from you, heading towards the nearest place for automobile service. Compare the pitch of the horn before he starts to drive away to the pitch you hear as he is driving away from you.
Lower.

You are riding your bicycle toward a stationary police car with a siren that is blaring away. Will the pitch of the siren sound lower, higher, or the same as it will sound when you actually stop your bicycle? (Assume the actual pitch of the siren stays constant.)
Higher.

You are standing near an interstate highway trying to talk on a pay phone. You have raised your voice because of the noise, so the loudness of your voice is about 80 decibels. The sound of the traffic on the highway is about 100 decibels. How many times larger is the intensity of the traffic’s sound waves compared to those of your voice?
100 times.

An amplifier can magnify the intensity of sound waves by a factor of 1,000. If a 30-decibel sound is fed into the amplifier, how many decibels will come out?
60.