Waves Part 2

Question 1

why do sounds travel faster in solids

Answer 1

molecules are closer together so less time needed to transfer energy to one another

Question 2

how do we hear sounds

Answer 2

sound waves cause ear drum and other parts to vibrate which causes the sensation of sound

Question 3

what frequency limits are human hearing

Answer 3

20 Hz to 20 kHz

Question 4

what are ultrasound waves

Answer 4

frequency higher than 20 kHz

Question 5

how can ultrasound waves be used to determine distances

Answer 5

• they are partially reflected when they meet a boundary between two different media
• time taken for reflections to reach a detector can be used to determine how far away such a boundary is
• it is used in SONAR, echolocation and medical ultrasounds

Question 6

describe P-waves

Answer 6

• longitudinal
• travel at different speeds through solids and liquids
• first waves after an earthquake

Question 7

describe S-waves

Answer 7

• transverse
• they are felt after P-waves
• cannot travel through liquid

Question 8

describe L-waves

Answer 8

• transverse
• only travel in the crust
• ‘love’ waves

Question 9

what is used to detect seismic waves

Answer 9

seisometer - can be used to find how far away from a detector the earthquake happened

Question 10

how can seisometers be used to determine the distance between detector and earthquake

Answer 10

• P-waves arrive before S-waves
• scientists already know speed of S-waves and P-waves
• the difference in the arrival time can be used to calculate the distance travelled from the focus of the earthquake

Question 11

how can epicentre of earthquake be located

Answer 11

• triangulation
• uses three detectors
• can pinpoint exact location as it is where the calculated distances from each detector overlaps

Question 12

how do scientists know the earth has a liquid outer core

Answer 12

• S-waves cannot travel through liquids
• shadow zones occur on the crust where S-waves are not detected but P-waves are
• suggests there is a liquid layer in earth that S-waves cannot penetrate

Question 13

what are electromagnetic waves

Answer 13

transverse waves that transfer energy from the source of the waves to the absorber

Question 14

what is the order of waves in the electromagnetic spectrum

Answer 14

radio waves
microwaves
infrared
visible light
ultra violet
x-rays
gamma rays

Question 15

how fast do electromagnetic waves travel

Answer 15

all travel at the same speed which in a vacuum is 300,000,000 m/s r 3x10^8 m/s

Question 16

how are radio waves produced

Answer 16

• produced by oscillations in A.C. electrical circuits
• if absorbed, they may create an alternating current with the same frequency as the radio itself
• radio waves can induce oscillations in an electrical circuit

Question 17

how are gamma waves produced

Answer 17

changes in the nucleus of an atom

Question 18

what are the units for radiation dose

Answer 18

Sieverts (Sv) - measure of risk of harm resulting from exposing the body to radiation

Question 19

dangers of uv waves

Answer 19

can cause skin to age prematurely and increase risk of skin cancer

Question 20

dangers of x-rays and gamma rays

Answer 20

ionising radiation that can causes mutations of genes and cancer

Question 21

uses of radio waves

Answer 21

tv and radio

Question 22

uses of microwaves

Answer 22

satellite communication
cooking food

Question 23

uses of infrared

Answer 23

electrical heaters
cooking food
infrared cameras

Question 24

uses of visible light

Answer 24

fibre optic communications

Question 25

uses of uv

Answer 25

energy efficient lamps
sun tanning
security marking - bank notes

Question 26

uses of x-rays and gamma rays

Answer 26

medical imaging and treatments
sterilising medical equipment to kill bacteria

Question 27

what do hot objects do

Answer 27

• emit and absorb infrared radiation no matter what temperature
• the hotter it is, the more infrared radiation it radiates

Question 28

what is a black body

Answer 28

• absorbs all radiation incident on it
• does not reflect or allow any radiation transmitted through it
• since it is a good absorber, it would also be a good emitter
• perfect black body would be best emitter

Question 29

describe emissions of object at a constant temperature

Answer 29

emits radiation across a continuous range of wavelengths

Question 30

What do the wavelengths and intensities of black body radiation depend on?

Answer 30

• temperature of the object
• hotter the object, greater the intensity of radiation emitted

Question 31

what is the condition for a body to be at a perfect temperature

Answer 31

• absorbing radiation at the same rate it is emitting it
• if temperature increases, it is absorbing more than it is emitting

Question 32

how does Earth remain a constant temperature

Answer 32

The temperature of the Earth is dependent on the rate of absorption of energy from the Sun, the rate of emission from the planet and the proportion of radiation that is reflected back into space.

Question 33

what is greenhouse effect

Answer 33

Gases in the atmosphere prevent energy from leaving the planet once it has been emitted from the surface (either via absorption or reflection back down to the surface).
Because of this, not as much energy is emitted from the planet as is transferred from the Sun and the planet warms up.