Doppler Effect and Sound Waves

The lecture introduces the Doppler effect, explaining how motion affects frequency perception. It covers the effect on sound and light, detailing how frequency changes with the movement of the source or observer. Equations for calculating these changes are provided, with examples illustrating the concepts. The lecture concludes with a discussion on sonic booms, caused by objects exceeding the speed of sound, and a summary of the key points.

What is the Doppler Effect?

• A change in amplitude due to motion of the source or observer

• A change in wavelength due to temperature changes

• A change in speed of sound due to pressure variations

• A change in frequency due to motion of the source or observer

When a vehicle with a siren is stationary, how do the sound waves reach the observers?

• The waves are compressed towards one observer

• The waves do not reach the observers

• The waves reach both observers at the same time

• The waves are expanded towards one observer

What happens to the sound waves when the source is moving towards an observer?

• The waves are compressed, resulting in a higher frequency

• The waves are stretched out, resulting in a lower frequency

• The waves are absorbed by the source

• The waves remain unchanged

Which sign is used in the Doppler Effect equation for an approaching source?

• Negative

• Positive

• Divisive

• Multiplicative

In the Doppler Effect equation, what does 'v sub w' represent?

• Speed of sound

• Speed of the source

• Wavelength of the sound

• Speed of the observer

If a train's horn has a frequency of 150 Hz and the train is moving towards an observer, what happens to the observed frequency?

• It fluctuates

• It remains the same

• It decreases

• It increases

What is the relative velocity between the train engineer and the train's horn?

• 35 meters per second

• 340 meters per second

• Zero

• 150 Hertz

What causes a sonic boom?

• Destructive interference of sound waves when the source exceeds the speed of sound

• The source moving slower than the speed of sound

• The source moving at the speed of light

• Constructive interference of sound waves when the source exceeds the speed of sound

What is the effect of constructive interference in a sonic boom?

• It reduces the sound intensity

• It creates a very strong sound that can break windows

• It cancels out the sound waves

• It has no effect on the sound

What happens to the sound waves when an aircraft exceeds the speed of sound?

• The sound waves travel ahead of the aircraft

• The sound waves remain behind the aircraft

• The sound waves disappear

• The sound waves slow down