Physics

Wave and Sound - 5 Session

Session Objectives

Session Objective Pitch of Sound Quality of sound Doppler Effect in Sound

Doppler’s Effect O f S f app O

Doppler’s Effect f app Observer(V o )Source

Class Test

Class Exercise - 1 The apparent frequency observed by an observer moving away from the source with the speed of sound is (a) same as original (b) more than original (c) less than original (d) None of these

Solution Hence answer is (d). In this case,. Hence, the observer will receive no sound.

Class Exercise - 2 When source and listener both move in the same direction, with same speed, the apparent frequency for observer is (a) same as original (b) more than original (c) less than original (d) None of these

Solution Hence answer is (a). Since relative velocity between observer and source is zero. Hence, there is no Doppler effect.

Class Exercise - 3 We distinguish between pleasant sound and unpleasant sound by referring to its (a) pitch(b) quality (c) frequency(d) None of these

Solution Hence answer is (b). Definition of quality of sound.

Class Exercise - 4 If frequency of source A is higher than frequency of source B, which source has lower pitch? (a) Source A (b) Source B (c) Both have same pitch (d) Nothing can be said about the pitch

Solution Hence answer is (b). High frequency means high pitch.

Class Exercise - 5 Due to Doppler effect, things which do not change is (a) frequency(b) pitch (c) wavelength(d) None of these

Solution Hence answer is (d). Frequency, pitch and wavelength change due to Doppler effect.

Class Exercise - 6 What happens to the pitch, when observer and source move at right angle to line joining them? (a) Does not change (b) Increases (c) Decreases (d) First increases then decreases

Solution Hence answer is (a). Component of their velocity along the line joining them is zero.

Class Exercise - 7 A train approaches a stationary observer with of the velocity of sound. The frequency of sound from train, observed by an observer on platform, is (Original frequency = 190 Hz) (a) 200 Hz(b) 100 Hz (c) 300 Hz(d) None of these

Solution Hence answer is (a).

Class Exercise - 8 Two engines pass each other in opposite directions with a velocity of 60 km/hr each. One of those engines emits a sound of frequency 540 Hz. The frequency heard in other engine after the engines have passed each other is (Speed of sound = m/s) (a) 408 Hz(b) 486 Hz (c) 386 Hz (d) 586 Hz

Solution Hence answer is (b).

Class Exercise - 9 What is the velocity of source if frequency appears to be double the original frequency to a stationary listener? (Velocity of sound = v)

Solution Hence answer is (a).

Class Exercise - 10 A source is moving towards a stationary observer. Which one is the true statement about the sound observed by the observer? (a) Pitch of sound is lower than original (b) Wavelength of sound is lower than original (c) Frequency of sound is lower than original (d) Speed of sound is lower than original

Solution Hence answer is (b). The frequency is higher. Hence, the wavelength is lower.

Thank you