SP4 Waves

Question 1

Define transverse waves

Answer 1

The vibrations are perpendicular to the direction to travel

Question 2

Define longitudinal waves

Answer 2

The vibrations are parallel to the direction of travel

Question 3

Examples of transverse waves

Answer 3

EM waves, S-waves, ripples/waves in water

Question 4

Examples of longitudinal waves

Answer 4

Sound waves, P-waves

Question 5

Describing waves

The amplitude is…

Answer 5

the displacement from the rest position to a peak or trough

Question 6

Describing waves

The period is…

Answer 6

the number of seconds it takes for one full cycle

Period = 1 / frequency

Question 7

Formula for wave speed

Answer 7

Wave speed = frequency x wavelength
OR
Wave speed = distance / time

Question 8

How do you measure velocity of sound in air?

Answer 8

By attaching a signal generator to a speaker, you can generate sounds with a specific frequency. Use two microphones and an oscilloscope to find the wavelength of the sound waves generated

Question 9

How do you measure the velocity waves on the surface if water?

Answer 9

Using a signal generator attached to the dipper of a ripple tank, you can create water waves at a set frequency. Then dim the lights and use a strobe light to see a wave pattern. Alter frequency of strobe light until wave pattern seems to “freeze”. The distance between each shadow line is equal to one wavelength. Measure distance between lines that are 10 wavelengths apart and find average

Question 10

What is refraction?

Answer 10

The change in direction of a wave at a boundary

Question 11

What happens when a wave travels along the normal?

Answer 11

It will change speed as it crosses a boundary, but it will not change direction (refraction)

Question 12

What happens when a wave hits the boundary at an angle?

Answer 12

The change of speed causes a change in direction because of the angle it has hit the boundary. This causes refraction

Question 13

Define specular reflection

Answer 13

Occurs when waves are reflected in a single direction by a smooth surface

Question 14

Define diffuse reflection

Answer 14

Occurs when waves are reflected by a rough surface and the waves are reflected in all directions

Question 15

What is reflection?

Answer 15

Where the incoming ray is neither absorbed nor transmitted, but instead is ‘sent back’ away from the second material - this is how echoes are created

Question 16

List the order in which the ear transmits vibrations

Answer 16

Eardrum, ossicles, semicircular canals, cochlea, auditory nerve

Question 17

What does your outer ear do?

Answer 17

Sound waves reach your ear drum and cause it to vibrate.

Question 18

What does your middle ear do?

Answer 18

Vibrations from drum are passed to tiny bones called ossicles, through the semicircular canals and t the cochlea

Question 19

What does your inner ear do?

Answer 19

The cochlea turns these vibrations into electrical signals which gets sent to your brain, that then interprets the signal as sounds of different pitches and volumes

Question 20

Limitations to human hearing

Answer 20

1) shape of eardrum
2) size of eardrum
3) structure of parts within ear that vibrate

Question 21

Why can human ear only detect a certain range of frequencies?

Answer 21

Depends on the range of lengths of hairs in the cochlea. As a person ages, the shorter hairs that respond to higher frequencies stop working

Question 22

A pulse of ultrasound takes 4.5 secs to travel from submarine to seabed and back again. If speed of sound in seawater is 1520 m/s, how far away is the submarine from the seabed?

Answer 22

4.55 / 2 = 2.25 secs there

1520 x 2.25 = 3420m away

Question 23

What is ultrasound?

Answer 23

Frequencies greater than 20,000 Hz

Question 24

How is ultrasound used in sonar?

Answer 24

In echo sounding, which is used by boats and submarines to find out the distance of the seabed / locate objects deep in water

Question 25

How is ultrasound used in body scanning?

Answer 25

Ultrasound waves can pass through the body, but whenever they reach a boundary between two different media, some of the wave is reflected back and detected

Question 26

How is ultrasound used in foetal scanning?

Answer 26

The exact timing and distribution of ultrasound echoes are processed by a computer to produce a video image of the foetus

Question 27

What is infrasound?

Answer 27

Frequencies lower than 20 Hz

Question 28

Uses of infrasound

Answer 28

1) animals communication
2) scientists can monitor infrasound that is produced during natural events eg. erupting volcanoes
3) earthquakes produce waves that can be used to explore structure of Earth

Question 29

Define P-waves inside the earth

Answer 29

Longitudinal, travel through solids and liquids, travel faster than S-waves

Question 30

Define S-waves inside the earth

Answer 30

Transverse, only travel through solids, slower than P-waves