Doppler Effect

What is the Doppler Effect?

• A change in frequency due to the relative motion of a wave source and an observer

• When a wave overlaps with another wave

• When a wave bounces off of another object

• When a wave bends due to traveling through a different medium

Short sound waves are...

• high pitched
• low pitched
• medium pitched

When the car moves AWAY from you, its horn seems...

• Low pitched
• High pitched
• Normal

What can you tell about the motion of this object?

• Moving left.
• Moving right quickly.
• Standing still. 
• Moving up slowly. 

You are standing on the side of the road when a police car races past you with its siren on. After the police car passes you, what happens to the pitch of the siren?

• It increases

• It decreases

• It turns red

Look at the picture. Who is experiencing a lower pitched sound?

• Observer A

• Observer B

• There is no difference

What energy is the longest wavelength?

• Radio

• Infrared

• X rays

• Gamma

An observer passes a 500 Hz sound source and moves away with a speed of 30 m/s.

• 456 Hz

• 544 Hz

• 460 Hz

• 548 Hz

Answer explanation

f₁ = f_o (c - v ) /c

= 500 x (340 -30)/340 = 456 Hz

• 0.98 m

• 0.76 m

• 0.85 m

• 1.34 m

An ambulance is travelling towards a hospital at a constant velocity of 30 m/s.The siren of the ambulance produces sound of frequency 400 Hz. Take the speed of sound in air as 340 m/s.

Calculate the frequency of the sound of the siren heard by a person standing at the hospital.

• 400 Hz

• 501.43 Hz

• 478.32 Hz

• 438.71 Hz