Doppler Effect and Harmonics

An ambulance is driving towards you as you stand on the sidewalk. What happens to the pitch of the siren as it comes towards you?

• It increases

• It decreases

You are driving in a car and honk the horn at a person standing in the street. As you approach the person, what happens to the pitch of the horn according to you in the car?

• It increases

• It decreases

• It stays the same because you are in the car moving with the sound.

A car is not moving but the horn is on. You run towards the car to investigate what's going on. As you approach the car, what happens to the frequency of the sound waves from the horn?

• They increase

• They decrease

A car moves at 20 m/s away from a whistle. The whistle is stationary. The whistle makes a sound with a frequency of 500 Hz. The speed of sound in air is 330 m/s.

What is the frequency observed by the driver of the car?

• 530 Hz

• 470 Hz

• 520 Hz

A car moves at 20 m/s towards a whistle. The whistle is stationary. The whistle makes a sound with a frequency of 500 Hz. The speed of sound in air is 330 m/s.

What is the frequency observed by the driver of the car?

• 530 Hz

• 470 Hz

• 480 Hz

An ambulance is moving towards a stationary listener at a constant speed of 30 m∙s-1 . The siren of the ambulance emits sound waves having a wavelength of 0,28 m. Take the speed of sound in air as 340 m∙s-1

Calculate the frequency of the sound waves emitted by the siren as heard by the ambulance driver.

An ambulance is moving towards a stationary listener at a constant speed of 30 m∙s-1 . The siren of the ambulance emits sound waves having a wavelength of 0,28 m. Take the speed of sound in air as 340 m∙s-1 .

Calculate the frequency of the sound waves emitted by the siren as heard by the listener.

Choose the correct answer.

The siren of the ambulance produces sound of frequency 400 Hz. Take the speed of sound in air as 340 m∙s-1. Calculate the wavelength of the sound.

• 0.98 m

• 0.76 m

• 0,85 m

• 1.34 m

An observer moves towards a source of sound at a speed of 30 ms^-1

If the frequency of the sound to a stationary observer is 500 Hz the frequency to the moving observer is

• 456 Hz

• 544 Hz

• 460 Hz

• 548 Hz

Answer explanation

f₁ = (c+v) f_o/c

= (340 + 30) x 500/340 = 544 Hz