Topic 6 - Waves (3)

Question 1

BLACK BODY RADIATION:
What is a perfect black body?

Answer 1

• an object that aborbs all the radiation that hits it
  (no radiation id reflected or transmitted)
• the best possible emitters of radiation

Question 2

BLACK BODY RADIATION:
Why do all objects emit electromagnetic (EM) radiation?

Answer 2

due to the energy in their thermal energy stores

Question 3

BLACK BODY RADIATION:
What does the intensity and distribution of the wavelengths emitted by an object depend on?

Answer 3

the object’s temperature

Question 4

BLACK BODY RADIATION:
What is intensity?

Answer 4

power per unit area
(how much energy is transferred to a certain area in a given amount of time)

Question 5

BLACK BODY RADIATION:
What happens to the intensity of the emmited wavelength’s as an object’s temperature increases?

Answer 5

the intensity increases

Question 6

BLACK BODY RADIATION:
What type of wavelength does intensity increase more rapidly for?
What does this cause?

Answer 6

shorter wavelengths
- this causes the peak wavelength (the wavelength with the highest intensity) to decrease

Question 7

BLACK BODY RADIATION:
What is the peak wavelength?

Answer 7

the wavelength with the highest intensity

Question 8

BLACK BODY RADIATION:
What does the temperature of the earth depend on?

Answer 8

the amount of radiation it reflects, absorbs and emits

Question 9

BLACK BODY RADIATION:
What causes an increase in local temperature?

Answer 9

during the day, lots of radiation (like light) is transfeered to the earth from the sun and absorbed

Question 10

BLACK BODY RADIATION:
What causes a decrease in local temperature?

Answer 10

at night, less radiation is being absorbed than being emitted

Question 11

BLACK BODY RADIATION:
How does the temperature of the earth stay fairly constant?

Answer 11

• some radiation is reflected by the atmosphere, clouds and the earth’s surface
• some radiation is absorbed by the atmosphere, clouds and the earth’s surface
• radiation is also emitted

Question 12

BLACK BODY RADIATION:
How do changes in the atmosphere cause a change in earth’s overall temperature?

Answer 12

if the atmosphere starts absorbing more radiation without emitting the same amount, the overall temperature will rise until emission and absorbtion are equal again

Question 13

INFRARED RADIATION AND TEMPERATURE:
What are all objects contiually doing/

Answer 13

emitting and absorbing infrared radiation (IR)
it is emitted from the surface of a an object

Question 14

INFRARED RADIATION AND TEMPERATURE:
How does the temperature of an object affect how much infrared radiation it radiates?

Answer 14

hotter objects radiate more IR radiation in a given time

Question 15

INFRARED RADIATION AND TEMPERATURE:
What happens to an object when it’s hotter than its surroundings?

Answer 15

it emits more IR radiation than it absorbs as it cools down

Question 16

INFRARED RADIATION AND TEMPERATURE:
Whar happens to an object when its cooler than its surroundings?

Answer 16

it absorbs more IR radiation than it emits as it warms up

Question 17

INFRARED RADIATION AND TEMPERATURE:
What is happening in objects that are at a constant temperature?

Answer 17

they emit infrared radiation at the same rate that they are absorbing it

Question 18

INFRARED RADIATION AND TEMPERATURE:
some colours and surfaces absorb and emit radiation better than others

Question 19

INFRARED RADIATION AND TEMPERATURE:
Which surfaces are better at absorbing and emitting radiation?
- black or white
- shiny or matt

Answer 19

black
matt

Question 20

ULTRASOUND:
What is ultrasound?

Answer 20

sound with frequencies higher than 20,000 Hz

Question 21

ULTRASOUND:
How is ultrasound made?

Answer 21

• electrical devices can be made which produce electrical oscillations over a range of frequencies
• these can easily be converted into mechanical vibrations to produce sound waves beyond the range of human hearing (frequencies above 20,000Hz)

Question 22

ULTRASOUND:
What is partial reflection?

Answer 22

when a wave passes from one medium to another, some of the wave is reflected off the boundary between the two media, and some is transmitted (and refracted)

(ultrasound waves get partially refracted at boundaries)

Question 23

ULTRASOUND:
How does the partial reflection of ultrasound make it useful?

Answer 23

• you can point a pulse of ultrasound at an object, at boundaries between substances, some of the ultrasound gets reflected back
• the time it takes for the reflections to reach the detector can be used to measure how far away the boundary is

Question 24

ULTRASOUND:
Name 3 uses of ultrasound?

Answer 24

• medical imaging
• industrial imaging
• echo sounding

Question 25

ULTRASOUND: How is ultrasound used in medical imaging?

Answer 25

for example, pre-natal scanning of a foetus - ultrasound can pass through the body, but whn it reches a boundary between two different media (like fluid in the womb or the skin of a foetus) some of the wave if reflected back and detected - the exact timing of these echoes are processed by a computer to produce a video image of the foetus

Question 25

ULTRASOUND: Why is ultrasound used in scanning of a foetus?

Answer 25

X- rays would be dangerous (although we don't know is ultrasound is safe in all cases)

Question 26

ULTRASOUND: How is ultrasound used in industrial imaging?

Answer 26

for example, finding flaws in materials - used to find flaws in objects such as pipes or materials such as wood or metal - ultrasound waves entering a material will usually be reflected by the far side of the material - if there is a flaw such as a crack inside the object, the wave will be reflected sooner

Question 27

ULTRASOUND: What is echo sounding used for?

Answer 27

used high frequency sound waves (including ultrasound) by boats and submarienes to foind out the depth of water or to locate objects in deep water

Question 28

EXPLORING STRUCTURES: What changes the properties of waves (e.g. speed)?

Answer 28

the material they're travelling through

Question 29

EXPLORING STRUCTURES: What are the different things that can happen when a wave arrives at a boundary between two materials?

Answer 29

- completely or partially reflected - continue travelling in the same direction but a different speed - refracted - absorbed

Question 30

EXPLORING STRUCTURES: What are the two main waves that can be used to understand structures?

Answer 30

ultasound seismic waves

Question 31

EXPLORING STRUCTURES: What is produced by an earthquake?

Answer 31

seismic waves (these travel through the earth)

Question 32

EXPLORING STRUCTURES: What do we use to detect seismic waves on the surface of the planet?

Answer 32

seismometers

Question 33

EXPLORING STRUCTURES: How do seismologists use seismometers?

Answer 33

they work out the time it takes for shock waves to reach each seismometer thye also note which parts of the earth don't receive shock waves at all

Question 34

EXPLORING STRUCTURES: What happens when seismic waves reach a boundary between different layers of material inside the earth?

Answer 34

some waves will be absorbed and some will be refracted

Question 35

EXPLORING STRUCTURES: What happens most of the time when waves are refracted? But what happens when the properties change suddenly?

Answer 35

they change speed gradually, resulting in a curved path the wave speed changes abruptly and the path has a kink

Question 36

EXPLORING STRUCTURES: What are the 4 layers of the earth?

Answer 36

- crust - mantle - liquid outer core - solid inner core

Question 37

EXPLORING STRUCTURES: What are the two different types of seismic waves?

Answer 37

P-waves S- waves

Question 38

EXPLORING STRUCTURES: How have scientists managed to understand the internal structure of the earth?

Answer 38

by observing how seismic waves are absorbed and refracted, scientists are able to work out where the properties of the earth change dramatically

Question 39

EXPLORING STRUCTURES: What are the three main properties of P-waves?

Answer 39

- longitudunal waves - travel through solids and liquids - travel faster than S - waves

Question 40

EXPLORING STRUCTURES: What are the 3 main properties of S-waves?

Answer 40

- they are transverse - can't travel through liquids or gases - slower than p-waves

Question 41

EXPLORING STRUCTURES: Look at diagram of p and s waves on p90