Question

1. Which of the following actions will increase the speed of sound in air? (a) decreasing the air temperature (b) increasing the frequency of the sound (c) increasing the air temperature (d) increasing the amplitude of the sound wave (e) reducing the pressure of the air. Why?

2. Suppose you’re on a hot air balloon ride, carrying a buzzer that emits a sound of frequency f. If you accidentally drop the buzzer over the side while the balloon is rising at constant speed, would the frequency and intensity of the sound you hear increase or decrease as the buzzer falls toward the ground? Why?

3. You are tuning a guitar by comparing the sound of the string with that of a standard tuning fork. You notice a beat frequency of 5 Hz when both sounds are present. As you tighten the guitar string, the beat frequency rises steadily to 8 Hz. To tune the string exactly to the tuning fork, you should (a) continue to tighten the string, (b) loosen the string, or (c) impossible to determine from the given information. Why?

Answer 1

1. The speed of sound in air will increase with the increase in air temperature. Hence option "c" is the correct answer.

Reason: Sound like heat is a form of kinetic energy. It is formed by a vibrating body. Sound is longitudinal mechanical wave. Molecules at higher enery will vibrate faster as they have more energy. As molecules vibrate faster, sound waves travel faster. Hence an increase in air temperature will result in increase in speed of sound.

We also know that velocity of sound in air is:

v_{sound in air} = 331.4 + 0.6T m/s

Since velocity of sound is directly proportional to temperature, it will increase with rise in temperature of the medium.

speed of sound in air at different temperatures:

At 0⁰ it's 331m/s while at room temperature it is 346 m/s, thus supporting our reasoning.