REFLECTION OF SOUND – ECHO

When do we hear echoes?

• When the emitted sound reaches the ear, the sound is reflected.

• When the emitted sound reaches the ear almost at the same time as the reflected sound.

• When the emitted sound reaches the ear before the reflected sound.

• All are correct

Which of the following objects is a good reflector of sound?

• Sweater

• Iron

• Sponge

• Sofa

Which of the following conclusions is correct?

• Good reflectors are objects with rough, rough surfaces.

• Poor reflectors are objects with smooth, hard surfaces.

• Objects that reflect sound well are large objects.

• Poor reflector of sound are soft, uneven objects.

A man stood 680 m from a cliff and shouted. How long after shouting does this person hear the echo back? Let the speed of sound in air be 340 m/s.

• 2s

• 1s

• 4s

• 6s

Is reflected sound beneficial or harmful?

• Disadvantage

• Advantage and benefit

• Disadvantage and harmful

• Advantage

• Advantage and harmful

To avoid the phenomenon of echo in the room, the room must have the following dimensions?

• Less than 11.5m

• Greater than 11.5m

• Less than 11.35m

• Greater than 11.35m

Which of the following is a good absorber of sound?

• Steel, wood, fabric

• Concrete, iron, cotton

• Stone, iron, steel

• Fabric, velvet, felt

People often use the reflection of ultrasound to determine the depth of the sea. Assume the ship emits a sonar and picks up its reflection from the seabed after 1 second. Calculate the approximate depth of the seabed, knowing the speed of ultrasonic propagation in water is 1500 m/s.

• 1500m

• 750m

• 500m

• 1000m