Reflection of Sound : Echo and Reverberation | Sound | Assessment | English | Grade 9

Why cinema halls are made with curved walls?

• To avoid multiple reflection of sound.

• To maintain the frequency of the sound.

• To have a proper amplified sound for the audience.

• To ensure equal distribution of sound among the audience.

Answer explanation

Walls in a cinema halls are curved to ensure equal distribution of sound among the audience.

A sound makes an angle of 20° with a flat reflecting surface.What will be the angle of reflection?

• 20°

• 90°

• 110°

• 70°

Answer explanation

Angle made with the flat reflecting surface = 20° So, angle of incidence = 90° - 20° = 70° Reflection of sound follows the laws of reflection of sound, so angle of reflection is equal to angle of reflection. Hence, angle of reflection = 70°

Why we cannot hear echoes in small rooms?

• Because the frequency of sound in a small room is not large enough.

• Because minimum distance criteria is not met in a small room.

• Because speed of sound keeps on changing due to presence of many reflecting surfaces.

• None of these

Answer explanation

Because for echo to take place there should be a minimum distance of 17.2 metre between the source of sound and the reflecting surface. So, echo does not takes place in a small room.

Riya claps in the front of a mountain and hears the echo after 4 seconds. What is the distance traveled by the sound, if the speed of air is 340 m/s?

• 680 metre

• 2720 metre

• 1360 metre

• 340 metre

Answer explanation

Speed of sound in air = 340 m/s Time = 4 seconds Distance travelled by the sound = 340 × 4 = 1360 m

What will happen if reververation goes on for a large amount of time?

• The pitch of the sound would increase due to increase in frequency.

• It would produce echoes.

• The sound cannot be heard.

• The sound becomes sharp.

Answer explanation

If the reservation goes on for large amount of time, it leads to produce echo.

Which of the following principles of sound is used in the stethoscope?

• Echo

• Multiple reflection

• Reverberation

• Reflection

Answer explanation

Stethoscope uses principle of multiple reflection.