TOPIC 4 - WAVES

Question 1

what are waves

Answer 1

Waves transfer energy and information without transferring matter

Question 2

Transverse vs longitudinal waves

Answer 2

• Longitudinal waves move parallel to direction of energy transfer
• Transverse waves move perpendicular to direction of energy transfer
• Longitudinal have compressions and rarefactions
• Transverse have peaks and troughs
• Longitudinal waves move in solids liquids gases
• Transverse waves move in solids only

Question 3

What is frequency

Answer 3

Number of wave cycles per second

Question 4

What is wavelength

Answer 4

Distance peak to peak or compression to compression

Question 5

What is period

Answer 5

Time taken to complete one wave cycle

Question 6

Equation linking time and frequency

Answer 6

Time = 1/f

Frequency = 1/T

Question 7

What is amplitude

Answer 7

Maximum displacement a point moves from rest position

Question 8

Equation for wave speed

Answer 8

frequency x wavelength

or

distance/time

Question 9

What can happen to waves when meeting a boundary?

Answer 9

1. Reflected
2. Refracted
3. Transmitted
4. Absorbed

Question 10

What is reflection

Answer 10

When wave ‘bounces off’ boundary and stays in their original medium.

Question 11

What is refraction

Answer 11

When wave changes speed and direction betweem 2 materials of different densities.

Question 12

What happens to light ray if moving from a less dense to a more dense medium

Answer 12

It slows down and refracts towards normal.

Question 13

What types are waves are sound waves

Answer 13

Longitudinal

Question 14

What happens when sound waves are passed through liquids and gases?

Answer 14

particles vibrate back and forth as wave passes through.

Question 15

What happens when sound waves are passed through solids?

Answer 15

Some energy is reflected, transmitted or absorbed. The sound wave causes changes in pressure on surface of the sold. It causes the particles in solid to vibrate (vibrations in solid can be longitudinal/transverse)

Question 16

How does the human ear detect sound waves?

Answer 16

1. sound waves enter ear canal
   2 sound waves make eardrum (thin membrane) vibrate
2. Vibrations are passed onto ossicles (tiny bones) that amplify vibrations
3. Vibrations are passed to liquid inside cochlea
4. Tiny hairs inside cochlea detect vibrations and create impulses (electrical signals)
5. Impulses travel along neurones in auditory nerve to reach the brain

Question 17

What is ultrasound

Answer 17

Frequency above 20 000Hz

Question 18

What is infrasound

Answer 18

Frequency below 20Hz

Question 19

What frequencies can humans detect

Answer 19

20-20 000Hz

Question 20

What are some uses of ultrasound

Answer 20

1. Sonar
2. Foetal scanning

Question 21

How does sonar work?

Answer 21

It uses ultrasound to detect objects underwater.
The pulse of ultrasound is sent underwater and is reflected off the ocean bottom.
The tiem it takes for the sound wave to return can be used to calculate depth.

Question 22

How does foetal scanning work?

Answer 22

1. Gel is used on the stomach to stop ultrasound just reflecting off the skin.
2. The transducer emits and recieves ultraosund waves.
3. Some waves are reflected back to the transducer when reaching different mediums like fat or bone.

Question 23

Why is foetal scanning safe?

Answer 23

It is not ionising like X-rays.

Question 24

What type of waves do earthquakes produce?

Answer 24

P-waves and S-waves

Question 25

Compare P-waves and S-waves

Answer 25

• Pwaves are longitudinal (can pass thru solids annd liquids)
• Swaves are transverse (only thru solids)
• S-waves can’t travel through (liquid) outer core
  -P waves can
• P-waves are faster, S-waves are slower

Question 26

How are seimsic waves detected?

Answer 26

They are detected by seisometer all around Earth.

Question 27

What are the discoveries made by seismic waves?

Answer 27

1. On the opposite side of the Earth to an earthquake, only P-waves are detected, not S-waves, suggesting mantle is solid as both waves pass through it, and suggesting outer core is liquid as no S-waves can penetrate it.
2. Refractions between layers cause 2 shadow zones, where no P-waves are detected, suggesting inner core is solid as size and positions of these shadow zones indicate large refraction taking place.

Question 28

What happens when sound waves moves from less dense to more dense medium?

Answer 28

The wavelength decreases, frequency stays the same, speed decreases