4th - Light And Sound

Question 1

What are light waves
Can they be reflected and refracted

Answer 1

Transverse
Yes

Question 2

What are sound waves
Can they be reflected And refracted

Answer 2

Longitudinal
Yes

Question 3

Law of reflection

Answer 3

Angle of incidence = angle of reflection

Question 4

Definition of a transverse wave

Answer 4

Oscillations are perpendicular to direction of energy transfer

Question 5

Definition of a longitudinal wave

Answer 5

Oscillations are parallel to direction of energy transfer

Question 6

What is refraction

Answer 6

Wave changing direction when it moves from one material to another
Due to the wave changing speed

Question 7

What happens to light when it enters a more dense material

Answer 7

Slows down
Turns towards the normal

Question 8

What happens to light when it enters a less dense material

Answer 8

Speeds up
Turns away from the normal

Question 9

Equation for refractive index

Answer 9

N = sin ( i ) / sin ( r )

(N = refractive index)

Question 10

• Practical
  How to investigate refractive index

Answer 10

• mark where ray enters glass block ( draw normal line at 90 degrees to surface)
• measure angle of incidence (protractor)
• mark exit point of ray -> show refracted ray
• measure angle of refraction (protractor)
• vary angle of incidence + measure angle of refraction
• repeat + take average
• plot graph of sin ( i) against sin (r)
• refractive index = gradient

Question 11

What does it mean when ray refracts at 90 degrees to normal

Answer 11

Angle of incidence = critical angle

Question 12

What does the ray undergo when
Angle of incidence > critical angle

Answer 12

Total internal reflection

Question 13

Equation to find critical angle

Answer 13

Sin ( c ) = 1 / n

Question 14

What is total internal reflection used for

Answer 14

In optical fibres to carry data

Question 15

What are optical fibres made of

Answer 15

Plastic or glass

Question 16

What does optical fibres have

Answer 16

Outer cladding - that has a lower refractive index than the inner core

Question 17

What does light do in an optical fibre

Answer 17

Totally internally reflect
Light will always hit a boundary at a value higher than c

Question 18

What happens to light in a right angled prism

Answer 18

Totally internally reflected

Question 19

Frequency range from human hearing

Answer 19

20 - 20,000 Hz

Question 20

What are frequencies greater than 20,000 Hz called

Answer 20

Ultrasound

Question 21

What are frequencies less than 20 Hz called

Answer 21

Infrasound

Question 22

What does higher frequency vibrations detected as

Answer 22

High pitch sounds

Question 23

What are higher amplitude vibrations detected as

Answer 23

High volume sounds

Question 24

*practical
Investigate speed of sound in air by clapping

Answer 24

• speed = distance / time
• measure at least 100m using trundle wheel
• one person holds stopwatch, other person claps
• measure time taken between seeing clap and hearing clap
• repeat and take average
• use equation

Question 25

*practical
Investigate speed of sound in air using a pair of microphones

Answer 25

• speed = distance / time
• measure at least 1m between two mics (meter rule)
• hit a metal plate with a hammer next to mic A
• measure time taken between mic A and B detecting sound (electronic timer)
• repeat and average
• equation

Question 26

What do oscilloscopes display sound waves as

Answer 26

A trace on a screen

Question 27

What do microphones convert travelling sound waves to

Answer 27

Electrical signals

Question 28

X and y axis on an oscilloscope

Answer 28

X - time
Y- amplitude

Question 29

How to find the frequency of a wave using an oscilloscope

Answer 29

• connect oscilloscope to microphone - get a steady trace
• get a minimum of 1 complete cycle on screen
• count number of squares for 1 complete cycle
• multiply no. Of squares by time base = time period
• frequency = 1 / time period