P13 Electromagnetic Spectrum

Question 1

what part of the electromagnetic spectrum can humans detect?

Answer 1

visible light

Question 2

what is the speed of all electromagnetic waves?

Answer 2

3 x 10^8 m/s

Question 3

what is meant by a ‘continuous spectrum’?

Answer 3

the cut off point between each type of wave is not always clear

Question 4

what are the waves in the electromagnetic spectrum?

Answer 4

gamma
x-ray
ultraviolet
visible
infrared
microwaves
radio

Question 5

how do the properties differ from the gamma end of the spectrum to the radio end of the spectrum?

Answer 5

gamma - high frequency with short wavelength
radio - low frequency with long wavelength

Question 6

what are electromagnetic waves?

Answer 6

transverse waves that transfer energy from a source to an absorber

Question 7

what are the properties of waves at the violet end of the visible light spectrum?

Answer 7

higher frequency with a shorter wavelength

Question 8

what are the properties of waves at the red end of the visible light spectrum?

Answer 8

lower frequency with a longer wavelength

Question 9

what happens when EM waves are generated or absorbed?

Answer 9

changes take place in the atom or nuclei of the atom

Question 10

how can EM waves be generated?

Answer 10

electrons move energy levels
changes take place in the nucleus

Question 11

what can EM waves be emitted and absorbed over?

Answer 11

they can be emitted or transmitted over a large range of frequencies

Question 12

what are the hazards of UV, X rays and gamma rays?

Answer 12

UV - increase the risk of skin cancer, age skin prematurely
gamma + x rays - ionising radiation. this can cause mutation of genes which increases risk of skin cancer

Question 13

how can radio waves be produced?

Answer 13

when electrons oscillate in electronic circuits

Question 14

how can radio waves transmit information?

Answer 14

radio waves can be transmitted to have the same frequency as an electrical circuit.
they can then be transmitted and then absorbed by an aerial and create an alternating current with the same frequency of the wave

Question 15

what are radio waves used for and why?

Answer 15

to transmit radio and terrestrial TV (TV received using an aerial) signals
they are used because they can travel long distances before being absorbed
they can also spread out between hills (diffraction)
they can also reflect off the ionoshpere so radio waves can travel long distances around the earth

Question 16

what are microwaves used for and why?

Answer 16

to heat food - water molecules absorb the microwaves’ energy
communicate with satellites in space - microwaves can travel through the atmosphere unaffected

Question 17

what can infrared be used for and why?

Answer 17

emitted by electrical heaters and heats food - infrared is easily absorbed by the surface of objects
infrared cameras

Question 18

what is visible light used for and why?

Answer 18

communications (fibre optic cables) - pulses of light are sent down optical fibres to transmit information. visible light has a short wavelength so can carry lots of information

Question 19

what is ultraviolet used for and why?

Answer 19

energy efficient light bulbs - UV has a shorter wavelength so can carry more energy than visible light. the energy of the UV is then absorbed by the surface of the bulb and converted to visible light. this requires less energy than using visible light
tanning beds - can cause premature ageing and increase risk of skin cancer

Question 20

what can X rays and gamma rays be used for and why?

Answer 20

medical imaging - very penetrative and X rays are absorbed by bones so we can see them in the scans
medical treatments

Question 21

what do all objects do with infrared radiation?

Answer 21

all objects, no matter what temperature, emit and absorb infrared radiation

Question 22

what does the wavelength and intensity of the radiation depend on?

Answer 22

the temperature of the object

Question 23

what is the wavelength of very hot objects?

Answer 23

they emit shorter wavelength radiation than cooler objects

Question 24

what is a perfect black body?

Answer 24

an object which absorbs all of the radiation incident on it
no radiation is reflected or transmitted

Question 25

what is the best possible emitter of radiation?

Answer 25

a perfect black body

Question 26

what happens if an object is warmer than the surroundings?

Answer 26

it will emit more radiation than it absorbs and the temperature of it will decrease

Question 27

what happens if an object is cooler than its surroundings?

Answer 27

it will absorb more radiation than it emits so its temperature will increase

Question 28

what is happening if an object is at a constant temperature?

Answer 28

it is absorbing radiation at the same rate as it is emitting it

Question 29

what happens to the infrared radiation from the Sun?

Answer 29

some is reflected back into space
the rest is absorbed by the Earth. the Earth then emits the radiation back into space. some of this radiation is re-radiated by greenhouse gases in the atmosphere

Question 30

what is happening due to human activity?

Answer 30

the levels of greenhouse gases is increasing which means more infrared radiation is being trapped