Topic 6b- Electromagnetic waves

Question 1

What is the electromagnetic spectrum?

Answer 1

The electromagnetic spectrum is a continuous spectrum of all the possible wavelengths of electromagnetic waves

Question 2

What are the different wavelengths going from lowest frequency to highest

Answer 2

• radiowaves
• micro-waves
• infrared
• visible light
• ultraviolet
• x-rays
• gamma-rays

Question 3

What is the approximate wavelength of visible light?

Answer 3

10^-7m

Question 4

What happens if an atom absorbs energy

Answer 4

If an atom absorbs energy, some of its electrons move to higher energy levels within the atom. When each electron falls back down to its original level, an electromagnetic wave is produced

Question 5

How are electromagnetic waves produced?

Answer 5

When an atom gains energy and it’s electrons move from a highe energy level back down to its original energy level

Question 6

How are gamma rays produced

Answer 6

Unstable nuclei breaking apart in nuclear decay (emmited from ‘daughter’ nucleus)

Question 7

How are radiowaves produced?

Answer 7

Using alternating current (AC). As the charges oscillate, they produce oscillating electric and magnetic fields (electromagnetic waves) which is what radiowaves are. The frequency of the radiowave produced will be equal to the frequency of the alternating current.

Question 8

How are radiowaves recieved?

Answer 8

The reciever absorbs the radiowaves. The energy carried by the waves is transferred to the kinetic energy stores of the electrons in the material of the reciever. This causes the electrons to oscillate and, if the reciever is part of a complete electrical circuit, it generates an alternating current. The current has the same frequency as the radiowave.

Question 9

What device is used to measure oscillations of a wave?

Answer 9

An oscilloscope

Question 10

What makes long-wave radio wavelengths suited to their use?
What is their approximate wavelength?

Answer 10

• they can be transmitted and recieved halfway round the world
• this is because they diffract (bend) around the world’s surface and around hills
• this means they can be recieved even if the reciever isn’t in the line of sight of the transmitter
• [wavelength → 1-10km]

Question 11

What makes short-wave radio wavelengths suited to their use?
What is their approximate wavelength?

Answer 11

• don’t diffract around the Earth’s curve
• can still be recieved at large distances
• reflected between the earth and the ionosphere
• Bluetooth uses short-wave radiowaves
• [wavelength → 10-100m]

Question 12

What are the properties of TV and FM radio waves?

Answer 12

• must be in direct sight of the transmitter
• don’t travel far through objects
• signal doesnt diffract round hills

Question 13

What are uses of microwaves (the waves)

Answer 13

• satelite communications (microwaves easily pass through Earth’s atmosphere)
• cooking in microwaves → the waves penetrate up to a few centimeters into the food before being absorbed and transferred into thermal energy

Question 14

What are uses of infrared radiation?

Answer 14

• innfrared cameras
• cooking
• electric heaters

Question 15

What are uses of visible light?

Answer 15

• fibre optic cables

Question 17

What are uses of ultraviolet radiation (UV)

Answer 17

• sun tanning lamps
• security ink
• energy efficient bulbs

Question 18

What are uses of x-rays and gamma rays?

Answer 18

• medical imaging
• medical treatment (e.g. radiotherapy)

Question 19

Which EM radiation is the most harmful?

Answer 19

Higher frequency e.g.

• UV
• x-rays
• gamma rays

Question 20

What is the radiation dose measured in?

Answer 20

sieverts

Question 21

What does radiation dose take into account

Answer 21

• total amount of radiation absorbed
• how harmful the type of radiation is
• the type of tissue absorbing the radiation

Question 22

What are opaque objects?

Answer 22

objects that absorb some wavelengths of light and reflect others (e.g. a red apple reflects the red light but absorbs the others)

Question 23

What is the difference between transparent and translucent objects?

Answer 23

• transparent objects transmit light in straight lines so you can see clearly thorugh them (e.g. clear glass)
• translucent objects transmit light but also scatter it so you can’t see clearly through them (e.g. frosted glass)

Question 24

What does the temperature of an object depend on?

Answer 24

The amount of infrared radiation it absorbs and emits

Question 25

What surface will absorb and emit the most infrared radiation?

Answer 25

A matt black surface

Question 26

What surface will absorb and emit the least infrared radation?

Answer 26

a shiny white surface

Question 27

How does radiation affect Earth’s temperature?

Answer 27

During the day, more radiation is absorbed than emitted causing it to be warmer, whereas at night more is emitted than absorbed causing the earth to cool

Question 28

What is a perfect black body?

Answer 28

A perfect black body is an object that absorbs all of the electromagnetic radiation that hits it. No radiation is reflected or transmitted by it.

Question 29

What is intensity (in reference to wavelengths?)

Answer 29

The power per unit area

Question 30

What is the correlation between temperature and intensity of wavelength?

Answer 30

As the temperature of an object increases, the intensity of every emmited wavelength increases too.

Question 31

What is the link between temperature and the distribution of wavelengths from an object?

Answer 31

As the temperature of an object increases, the peak wavelength decreases (i.e. the wavelengths are shorter)