6.2 Reflection of Sound [Should do]

Which statement describes what happens to a sound to make an echo?

• The pitch of the sound increases

• The loudness of the sound decreases

• The sound gets reflected

• The sound gets louder

Which one of these will give the best echo in a room? All of the materials have the same area.

• soft curtains

• glass window

• thick carpet

• wool blanket

Zara has an empty room where she can practice playing her drums. Which one of these materials could she put on the walls to stop echoes when she plays?

• flat wood sheets

• shiny metal sheets

• soft thick curtains

• large flat mirrors

Where will Arun hear more echoes and why?

• In a large empty hall, because sound reflects off the walls.

• In a small carpeted room, because sound is absorbed by the carpet.

• In an open field, because there are no obstacles.

• In a forest, because trees reflect sound.

A fishing boat uses an echo to find the distance from the boat to some fish. A sound is sent from the ship to the fish. The sound reflects back to the ship. The speed of sound in water is 1500 metres per second. The time taken for the sound to go from the ship and back to the ship is 0.4 seconds. Use this equation to calculate the distance from the boat to the fish: Distance = speed x time [Remember that the distance travelled by the sound wave in 0.4 seconds is from the ship to the fish and back again.]

The speed of sound in air is 340 metres per second. Sofia stands 85 metres away from a tall cliff. She bangs a drum loudly. Calculate the time, in seconds, until she hears the echo of the drum.

Use the equation: Time in second = distance in metres / speed in metres per second.

.

• 0.5 seconds

• 0.25 seconds

• 1 second

• 2 seconds

A submarine is a ship that travels under water. At night or in deep water, people in submarines cannot see what is in front of the submarine. A submarine can use echoes of sound to detect objects in the water by:

• Using sound waves that bounce off objects and return as echoes

• Using light beams to see through water

• Releasing bubbles to detect obstacles

• Using magnets to find metal objects

The submarine emits a ​ (a)   . The sound wave travels through the water and reflects off the (b)   . The sound wave arrives back at the ​ (c)   . The time between the sound wave being emitted and received can be used to work out the ​ (d)   to the rock.

• sound wave
• rock
• submarine
• distance
• water wave
• water
• speed

A girl sees the lightning in a thunderstorm 8 seconds before she hears the thunder. If sound travels at 340 m/s in air, how far away is the thunderstorm?

• 2,040 m

• 1,360 m

• 2,720 m

• 3,400 m

A boy is standing 400 m away from a cliff. He makes a loud noise. If sound travels at 340 m/s, how long will it be before he hears the echo?

• 1.18 s

• 2.35 s

• 0.59 s

• 3.00 s