Chapter 12 - Wave properties

Question 1

3 examples of mechanical waves

Answer 1

Sound waves, ocean waves, seismic waves

Question 2

What are mechanical waves?

Answer 2

Waves that require a medium like water or air.

Question 3

3 examples of electromagnetic waves?

Answer 3

Light, radio, microwaves

Question 4

What are electromagnetic waves?

Answer 4

Waves that don’t require a medium. They can travel through a vacuum at 300,000,000 m/s

Question 5

What are the 2 areas on a transverse wave?

Answer 5

Compression and Rarefaction.

Question 6

What is a transverse wave?

Answer 6

A wave where the oscillations are perpendicular to the direction of energy transfer.

Question 7

What is a longitudinal wave?

Answer 7

A wave where the oscillations are parallel to the direction of energy transfer.

Question 8

What is the amplitude of a wave?

Answer 8

The max displacement of a point on a wave from its undisturbed position. The greater the amplitude the more energy the waves carry.

Question 9

What is the wavelength of a wave?

Answer 9

The displacement between a point on a wave and the same point on an adjacent wave.

Question 10

What is frequency?

Answer 10

The number of waves passing a fixed point per second.

Question 11

What is the time period?

Answer 11

The time taken for each wave to pass a fixed point.

Question 12

How can you measure the speed of sound in the air?

Answer 12

Have two people stand on opposite ends of a field at a measured distance apart. They should be as far apart as possible but still within sight of each other. Have one person bang two cymbals together. Use a stopwatch to measure the time interval between seeing the impact and hearing the sound. Use speed = distance/time

Question 13

What is refraction of waves?

Answer 13

The change of the direction in which they are travelling when they cross a boundary between one medium and another.

Question 14

Why does refraction happen?

Answer 14

When plane waves cross a boundary at a non-zero angle to the boundary, each wavefront experiences a change in speed and direction. The refracted waves have the same frequency, but different speeds, so they must have different wavelengths.

Question 15

What 3 things can happen to a wave entering an object?

Answer 15

1 - Refected - dependent on the wave and type of surface.
2 - absorbed - the substance gains energy from the waves and heats up.
3 - transmitted - if they are not absorbed, they will leave the other side.

Question 16

What range of sound can humans hear?

Answer 16

20Hz - 20,000Hz

Question 17

How do humans hear?

Answer 17

Sound waves make the eardrum vibrate which sends signals to the brain.

Question 18

Why is the frequency range for human ears limited?

Answer 18

Sound waves entering a solid are converted to vibrations and travel through the solid as vibrations. The conversion of sound waves to vibrations by solids only works over a limited frequency range.

Question 19

How does echo-sounding work?

Answer 19

They send high-frequency pulses of sound to deflect objects in deep water and measure water depth below a ship.

Question 20

What is an echo?

Answer 20

The reflection of sound waves from a smooth surface.

Question 21

What is ultrasound?

Answer 21

Sound above 20,000Hz

Question 22

2 uses of ultrasound

Answer 22

Pregnancy scans
Imagry of oragns

Question 23

3 things that make up a sound machine?

Answer 23

A transducer is placed on the body surface, a control system, a display screen.

Question 24

What advantages of ultrasound over X-rays?

Answer 24

It is partially reflected at boundaries between different types of tissue - some is reflected, some is absorbed, so can scan tissue.

It is non-ionising

Question 25

How can ultrasound be used in industrial imaging?

Answer 25

Flaws in metal castings can be detected using ultrasound waves. For example, if there is an internal crack, this creates a boundary inside the metal and the ultrasound waves are partially reflected from this boundary

Question 26

Earths structure.

Answer 26

A solid inner crust, a mantle (molton), a liquid outer core and a solid inner core.

Question 27

3 types of seismic waves

Answer 27

1. P-waves (primary waves) cause the initial tremors. They are longitudinal waves that push or pull on material as they move through the earth
2. S-waves (secondary waves) cause more tremors a few minutes later and are transverse waves which travel much more slowly than P-waves
3. L-waves arrive last and cause violent movements on the surface up and down as well as backwards and forwards. They only happen in the earth’s crust

Question 28

How can seismometer readings be used to locate the epicentre?

Answer 28

P-waves and s-waves bend as they travel through the mantle because their speed changes gradually with depth. P-waves refract at the boundary between the mantle and outer core because their speed changes abruptly. S-waves can’t travel through the liquid outer
core

Question 29

What is the shadow zone?

Answer 29

It is a zone from about 105 degrees to 142 degrees where no seismic waves are detected.

Question 30

How does the existence of a showdown zone prove the idea of a liquid outer core?

Answer 30

P waves are refracted at the boundary between the mantle and outer core when the waves enter the core and when they leave the core. Because the second refraction is further around, P-waves can’t reach the shadow zone. S-waves can’t travel through the outer core as it is liquid and they are transverse

Question 31

How does the shadow zone prove the existence of a solid inner core?

Answer 31

Weak p-waves detected in the shadow zone show that the core has a solid inner part that refracts p-waves at the boundary between the outer core and inner core into the shadow zone

Question 32

When was the boundary between the crust and mantle discovered?

Answer 32

When it was found that the speed of seismic waves changed about 50km below the surface.