p13 - electromagnetic waves

Question 1

define electromagnetic waves

Answer 1

• electric and magnetic disturbances
• travel as waves and transfer energy from a source to an absorber

Question 2

how are electromagetic waves grouped?

Answer 2

from longest wavelength, smallest frequency to shortest wavelength and highest frequency

Question 3

give order of electromagnetic waves

Answer 3

• radio waves (wavelengths upto 10^4 m)
• microwaves
• infrared radiation
• visible light
• ultra violet
• x rays
• gamma rays (wavelengths as short as 10 to the power of -15)

Question 4

the higher the frequency of an electromagnetic wave…

Answer 4

the more energy it transfers

Question 5

give equation for wavespeed

Answer 5

v = f x wavelength
wavespeed (electromagnetic: 3 x 10^8 m/s) = frequency (Hz) x wavelength (m)

Question 6

define visible light

Answer 6

• each colour has a different wavelength which increases fron violet to red
• using different shades and colours within visible light is important in photography

Question 7

define white light

Answer 7

mixture of all the colours in visible lights

Question 8

define infrared radiation

Answer 8

• emitted by all objects
• hotter the object, the more radiation it emits
• used in remote controls for TVs and DVD players
• can be transmitted along optical fibres, used in special cameras to see in dark

Question 9

define microwaves

Answer 9

• used in communications
• microwave transmitters produce wavelengths that can pass through atmosphere
• used to send signals to and from satellites for TV programmes
• used in microwave ovens for heating food

Question 10

define radio waves

Answer 10

used to transmit radio and TV programmes

Question 11

what radiation do mobile phones use?

Answer 11

• microwave radiation
• radio-waves at near microwave frequencies

Question 12

give a hazard of microwave and radio wave radiation

Answer 12

• penetrate skin and absorbed by body tissue causing internal heating that is very damaging

Question 13

give a hazard of infrared radiation

Answer 13

• absorbed by skin and too much causes burns

Question 14

define carrier waves

Answer 14

waves used to transfer any signal

Question 15

why are the radio and microwave spectrum divided into different bands

Answer 15

different bands used for differenct communications purposes

Question 16

the shorter the wavelength of the waves…

Answer 16

• the more information they carry
• the shorter their range
• the less they spread out

Question 17

why are microwaves used for satellite phone and TV signals?

Answer 17

they can travel between satellites in space and Earth

Question 18

why are optical fibres carrying visible light of infrared radiation useful in communications?

Answer 18

• they carry much more information that radio and microwave transmissions
• more secure because waves stay in fibre

Question 19

define an audio signal

Answer 19

• produced by a microphone when sound waves reach it
• used to modulate carrier waves

Question 20

how are carrier waves used to transmit information?

Answer 20

1) M - audio signals modulate carrier waves
2) S - supplied by transmitter waves
3) I - radio waves induce AC current
4) S - reciever circuits separates audio signals from carrier circuits
5) S - audio signal supplied to loudspeaker
6) E - emits sound waves

Question 21

define ultraviolet waves

Answer 21

• used for security marking and sunbeds
• cause sunburn and skin cancer
• may be harmful to human eyes

Question 22

define x-rays

Answer 22

• used to make images of bones to check for fractures
• to detect cracks in metal objects

Question 23

define gamma rays

Answer 23

• used to kill harmful bacteria in food to prevent food poisoning
• to sterilise surgical instruments
• may cause cancer but can also kill cancer cells

Question 24

what happens when gamma and x-rays pass through substances?

Answer 24

• knock electrons out of atoms in substances
• leaves atoms with a positive charge
• process called ionisation
• kills or damages living cells

Question 25

what are lead screens used for and why does this work?

Answer 25

• to shield people who work with x-rays and gamma rays
• this works because lead absorbs x-rays and gamma rays

Question 26

define a ‘film badge’

Answer 26

for people who work with ionising radiation to monitor worker’s exposure to it

Question 27

how can x-rays check for bone fractures and x-ray problems?

Answer 27

• pass through soft tissure but absorbed by bones, teeth (and metal objects)

Question 28

define charge-couples devices

Answer 28

an electronic device creating an electronic signal from an optical image formed on the CCD’s array of pixels

Question 29

how can soft organs be seen on x-ray image?

Answer 29

filled with a contrast medium tht absorbs x-rays

Question 30

define radiation dose

Answer 30

measure of damage done by radiation

Question 31

how can cancerous cells be destroyed?

Answer 31

by using high energy x-rays