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Reflection, ultrasound and seismic waves: GCSE Combined Science Physics practice questions

Foundation and Higher · Grade 6

A second set of questions on reflection, ultrasound and seismic waves. They are different from the ones on the topic page. Try each, then open the answer and compare your working.

More questions

Question 1 Hard

Explain why S waves are not detected on the far side of the Earth.

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Answer: S waves cannot travel through liquid, and the outer core is liquid, so it blocks them.

  1. S waves cannot pass through liquids.
  2. The outer core is liquid, so it blocks them.

Question 2 Hard

Explain why the distance to a wall is half of the speed of sound multiplied by the time for the echo.

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Answer: The sound travels to the wall and back, so the total distance is twice the distance to the wall.

  1. The sound travels to the wall and back.
  2. The total distance is twice the distance to the wall.

Question 3 Hard

Explain why a rough wall scatters light in many directions but a mirror does not.

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Answer: The rough surface has normals pointing in many directions, so rays reflect in many directions.

  1. A rough surface has many different angles.
  2. Each ray follows the law of reflection but the normals point in different directions.

Question 4 Hard

A person shouts towards a cliff and hears the echo 1.0 s later. Sound travels at 340 m/s in air. Work out how far away the cliff is.

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Answer: 170 m

  1. distance = speed × time ÷ 2
  2. 340 × 1.0 ÷ 2 = 170 m

Quick checks

Short questions with options. Choose one before you open the answer.

Check 1

What is the law of reflection?

  1. the angle of reflection is twice the angle of incidence
  2. the angle of incidence equals the angle of reflection
  3. the two angles always add up to 90°
Show answer

the angle of incidence equals the angle of reflection The angle of incidence equals the angle of reflection.

Check 2

From what line are the angles of incidence and reflection measured?

  1. the normal
  2. the surface of the mirror
  3. the horizontal
Show answer

the normal The normal, a line at right angles to the surface.

Check 3

What is the angle of incidence?

  1. the angle between the ray and the mirror surface
  2. the angle between the two rays
  3. the angle between the incoming ray and the normal
Show answer

the angle between the incoming ray and the normal The angle between the incoming ray and the normal.

Check 4

What is diffuse reflection?

  1. rays bounce off in one direction from a smooth surface
  2. rays scatter in many directions from a rough surface
  3. rays are absorbed by the surface
Show answer

rays scatter in many directions from a rough surface Reflection from a rough surface, where the rays scatter in many directions.

Check 5

Why can you read a page from any seat in a room?

  1. paper scatters light in many directions
  2. paper is a mirror
  3. paper makes its own light
Show answer

paper scatters light in many directions The paper is rough, so the light scatters in many directions and some always reaches you.

Check 6

What is ultrasound?

  1. sound below 20 Hz
  2. light that cannot be seen
  3. sound above 20 000 Hz
Show answer

sound above 20 000 Hz Sound with a frequency above 20 000 Hz.

Check 7

What range of frequencies can humans hear?

  1. about 2 Hz to 200 Hz
  2. about 20 Hz to 20 000 Hz
  3. about 20 000 Hz to 200 000 Hz
Show answer

about 20 Hz to 20 000 Hz About 20 Hz to 20 000 Hz.

Check 8

What happens when ultrasound reaches a boundary between two different materials?

  1. some of it is reflected
  2. all of it is absorbed
  3. none of it is reflected
Show answer

some of it is reflected Some of it is reflected and the rest carries on.

Check 9

Why is ultrasound safe to use on an unborn baby?

  1. it is very loud
  2. it is a type of X-ray
  3. it is not ionising
Show answer

it is not ionising It is not ionising, so it does not damage cells.

Check 10

Why is gel put on the skin before an ultrasound scan?

  1. it keeps the baby warm
  2. it stops air reflecting the ultrasound at the skin
  3. it makes the sound louder
Show answer

it stops air reflecting the ultrasound at the skin It removes the layer of air, so the ultrasound goes into the body instead of reflecting at the skin.

Check 11

What is echo sounding?

  1. using echoes to measure the depth of the sea
  2. using sound to heat the sea
  3. using light to measure depth
Show answer

using echoes to measure the depth of the sea Using the time for an ultrasound echo to return to measure the depth of water.

Check 12

Write the echo equation for distance.

  1. distance = speed × time
  2. distance = speed ÷ time
  3. distance = speed × time ÷ 2
Show answer

distance = speed × time ÷ 2 distance = speed × time ÷ 2.

Check 13

Why do you halve the distance in an echo calculation?

  1. the echo is quieter
  2. the sound travels there and back
  3. sound is slower on the way back
Show answer

the sound travels there and back The sound travels there and back, so the total is twice the distance.

Check 14

Roughly how fast does sound travel in air?

  1. 340 m/s
  2. 34 m/s
  3. 3400 m/s
Show answer

340 m/s About 340 m/s.

Check 15

Roughly how fast does sound travel in water?

  1. 340 m/s
  2. 15 m/s
  3. 1500 m/s
Show answer

1500 m/s About 1500 m/s.

Check 16

An echo returns after 0.2 s in air where sound travels at 340 m/s. How far away is the wall?

  1. 68 m
  2. 34 m
  3. 1700 m
Show answer

34 m 340 × 0.2 ÷ 2 = 34 m.

Check 17

A pulse returns from the sea bed after 0.08 s in water at 1500 m/s. How deep is the water?

  1. 60 m
  2. 120 m
  3. 18 750 m
Show answer

60 m 1500 × 0.08 ÷ 2 = 60 m.

Check 18

Higher tier. What type of wave is a P wave?

  1. transverse
  2. electromagnetic
  3. longitudinal
Show answer

longitudinal A longitudinal wave that can travel through solids and liquids.

Check 19

Higher tier. What type of wave is an S wave?

  1. longitudinal
  2. transverse
  3. ultrasound
Show answer

transverse A transverse wave that can travel only through solids.

Check 20

Higher tier. Which seismic waves travel through liquids?

  1. P waves
  2. S waves
  3. both P waves and S waves
Show answer

P waves P waves. S waves cannot.

Check 21

Higher tier. Which seismic waves arrive first at a detector?

  1. S waves
  2. they arrive together
  3. P waves
Show answer

P waves P waves, because they are faster than S waves.

Check 22

Higher tier. Why are S waves not detected on the far side of the Earth?

  1. they are too fast to detect
  2. they cannot pass through the liquid outer core
  3. the crust absorbs them
Show answer

they cannot pass through the liquid outer core They cannot pass through the liquid outer core.

Check 23

What is wrong with this: 'The echo took 0.5 s and sound goes 340 m/s, so the wall is 170 m away.'

  1. it forgot to halve, so the wall is 85 m away
  2. nothing, 170 m is right
  3. it should be 680 m
Show answer

it forgot to halve, so the wall is 85 m away 340 × 0.5 = 170 m is the distance there and back. The wall is half of that, 85 m.

Check 24

Why does a rough wall scatter light but a mirror gives a clear image?

  1. a rough surface does not obey the law of reflection
  2. a mirror absorbs the light
  3. a rough surface has normals pointing in many directions
Show answer

a rough surface has normals pointing in many directions A rough surface has normals pointing in many directions, so the rays reflect in many directions.

Keep going with Reflection, ultrasound and seismic waves

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