Waves Pt2

Question 1

Visible light

Answer 1

Have a very large range
Violets at 400nm
Reds at 700nm
Can mix to make other colours other than rgb (primary)

Question 2

Opaque objects

Answer 2

Do not transmit light
Colour depends on which wavelengths are most strongly reflected
White reflect all equally, black absorb all
Transparent and translucent do transmit, some wavelengths may on,y be absorbed or reflected by these

Question 3

Filters

Answer 3

Only transmit certain wavelengths
Primary colour filter only transmits that colour
Filters that aren’t primary allow that colour and the colour that make it

Question 4

Colour mixing

Answer 4

Green plus blue to cyan
Blue plus red to magenta
Red plus green to yellow

Question 5

What surfaces absorb and emit better

Answer 5

Black over white

Matt over shiny

Question 6

Perfect Black body

Answer 6

Doesn’t exist
An object that absorbs all radiation that hits it
Intensity and distribution of wavelengths emitted depend on temp
As it increases intensity of emitted wavelengths increases
Increases more for short wavelengths to cause the peak wavelength to decrease

Question 7

How does radiation affect the earth’s temperature

Answer 7

During the day lots is transmitted to earth and is absorbed
At night less is absorbed than is being emitted
Overall it stays fairly consistent
Atmosphere changes affect overall temperature if it starts to absorb more

Question 8

Sound waves

Answer 8

Caused by vibrating objects which are passed in compressions and rarefractions
Travels fastest in solids
Can’t travel in space as vacuum
May hear in ear drum

Question 9

The ear

Answer 9

Sound waves causes the ear drum to vibrate
Passed on to ting bones ossicles through canals to the cochlea
Turns them into electrical signals for the brain to sense
Humans hear 20Hz-20kHz

Question 10

Sound waves reflection and refraction

Answer 10

Reflected by hard flat surfaces (Echoes)

Refract as they enter different media

Question 11

Ultrasound

Answer 11

Sounds over 20kHz ( we can’t hear)
Partially reflected as some is always reflected back, time it takes to reach a detector tells us how far away a boundary is

Question 12

Ultrasound medical imaging

Answer 12

Pass through the body but some is reflected at a boundary between media and is detected
Exact timing is processed
E.g. foetus-womb

Question 13

Ultrasound industrial imaging

Answer 13

Can be used to find flaws in pipes or materials
Reflected by the fat side
If there is a flaw it will be reflected sooner

Question 14

Seismic waves

Answer 14

If there is an earthquake seismic waves travel through the earth, detected using seismometers
Seismologists work out where the earthquake was based on time taken to reach and where it didn’t reach
Some are absorbed and some refracted at boundaries in the earth, most change speed slowly for a curve but some quick for a kink

Question 15

Types of seismic waves

Answer 15

P-waves and S-waves
P-waves travel through core and are detected at top sides and bottom to tell us where it is
S-waves only the top sides
P-waves longitudinal, travel through solids and liquids, faster
S-waves transverse, only through solids and slower

Question 16

Superposition of waves

Answer 16

If two waves meet at the same point, they briefly superpose to appear as one wave

Question 17

Constructive interference

Answer 17

When the combined amplitude is larger than the amplitude of the individual waves

Question 18

Destructive interference

Answer 18

When the amplitude of the combined wave is smaller than those of the individual waves

Question 19

Diffraction

Answer 19

Waves spread out when they pass through a gap so they may curve at the edges or be fully curved depending on the gap they have

Question 20

Diffraction through a gap wider than wavelength

Answer 20

Little diffraction, waves still pretty much straight. Forms a diffracted pattern of bright areas and dark patches.

Question 21

Gap a bit wider than wavelength, diffraction

Answer 21

Small diffraction at the edges but the middle is straight. Forms a diffracted pattern of bright areas and dark patches.

Question 22

Diffraction with gap the size of wavelength

Answer 22

The waves are semi-circles from the line increasing in size as you move away. Forms a diffracted pattern of bright areas and dark patches. Maximum diffraction.

Question 23

Snell’s law

Answer 23

Refractive index (n) = sin i / sin r

i = angle of incidence
r = angle of refraction