electromagnetic spectrum p. 52 - grey college · electromagnetic spectrum p. 52. electromagnetic...
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Electromagnetic spectrum p. 52
Electromagnetic spectrum
frequency wavelength
lowest longest
highest shortest
redorangeyellowgreen
blueindigoviolet
Visible light
Infrared
Microwaves
Radio waves
Gamma rays (𝛾 − 𝑟𝑎𝑦𝑠)
X-rays
Ultraviolet
𝑣 = 𝜆𝑓𝑐 = 𝜆𝑓Speed of light
(electromagnetic waves)3 x 108 m.s-1
Wavelength in m
Frequency in Hz
Wave equation
𝑐 = 𝜆𝑓
ExampleCalculate the frequency of an electromagnetic wave with a wavelength of 3,2 nm.
m = x 10-3
𝜇 = x 10-6
n = x 10-9
p = x 10-12
3 x 108 = 3,2 x 10-9 x 𝑓
𝑓= 9,38 x 1016 Hz
Uses of electromagnetic waves,p. 54
Radio waves:
• Radio and TV-broadcasts• Detecting information around the
world• Communication
Uses of electromagnetic waves,p. 54
Microwaves:
• Microwave ovens• Satellite communication• Radar / position control of aeroplanes
Uses of electromagnetic waves,p. 54
Infrared:
• Transfer of energy and heat• Navigation • Conventional ovens• Remote controls
Uses of electromagnetic waves,p. 54
Visible light:
• Production of food in plants (photosynthesis)
• Enables us to see things around us
Uses of electromagnetic waves,p. 54
Ultraviolet light:
• Detecting false banknotes• Lighting
Uses of electromagnetic waves,p. 54
X-rays:
• Medical imaging• Security control
Uses of electromagnetic waves,p. 54
Gamma rays:
• Kills cancer cells• Sterilisation of equipment • Increases shelf life of food
Penetrating ability of the different kinds of electromagnetic radiation
Visible light
UV light
X-rays
Gamma-rays
Increase in
En
ergy
Dangers
UV-rays: skin aging , DNA-change, skin cancer (UVB is more damaging than UVA)
X-rays: extended exposure can cause cancer and cell damage
Gamma rays: can cause serious damage to DNA, different types of cancers
A photon as a parcel of energy found in light.
Particle nature of electromagnetic radiation
Relationship between the energy of a photon and the frequency and wavelength of the light.
𝐸 = ℎ𝑓
Energy in joule (J)
Planck’s constant (6,63 x 10-34 J.s)
Frequency in Hz
𝑐 = 𝑓𝜆
i.e. 𝑓 = 𝑐
𝜆
Therefore 𝐸 = ℎ𝑓 = ℎ𝑐
𝜆
𝐸 = ℎ𝑓
ExampleCalculate the energy of photon witha frequency of 2,45 GHz.
k = x 103
𝑀 = x 106
G = x 109
T = x 1012
= 6,63 x 10-34 x 2,45 x 109
= 1,62 x 10-24 J
Homework
p. 59,nos. 6, 7, 11.4, 11.5, 15
6.1 Write down the wave equation for electromagnetic radiationin the approved symbols.
𝑐 = 𝑓𝜆
6.2 The frequency of an electromagnetic wave is 6 x 1016 Hz.What is the wavelength of the wave in air?
𝑐 = 𝜆𝑓
3 × 108 = 𝜆 × 6 × 1016
𝜆 = 5 × 10−9 m
6.3 The period of a electromagnetic wave is 4 x 10-14 s. Calculatethe wavelength of the wave in air.
𝑐 = λf
3 × 108 = λ x 2,5 x 1013
𝜆 = 1,2 × 10−5 m
𝑓 =1
𝑇
=1
4 × 10−14
= 2,5 × 1013 𝐻𝑧
7. Charges in the antenna of a radio transmitter oscillate with a frequency of 650 kHz, while another one has a frequency of120 MHz. Which electromagnetic wave has the highest frequency?
𝑅𝑎𝑑𝑖𝑜 1:650 𝑘𝐻𝑧
= 650 x 103 Hz= 650 000 Hz
𝑅𝑎𝑑𝑖𝑜 2:120 𝑀𝐻𝑧
= 120 x 106 Hz= 120 000 000 Hz
𝑅𝑎𝑑𝑖𝑜 2 has the highest frequency.
11.4 All electromagnetic waves move at the same speed of300 million m.s-1. Calculate the frequency of X-rays witha wavelength of 5 × 10−10 m.
𝑐 = 𝑓𝜆
3 × 108 = 𝑓 × 5 × 10−10
𝑓 = 6 × 1017 Hz
11.5 It takes about 8,5 seconds for light from the Sun to reach theEarth. Calculate the distance (in meter) between the Sun andthe Earth.
𝑠𝑝𝑒𝑒𝑑 =𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑡𝑖𝑚𝑒
3 × 108 =𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
8,5
distance = 2,55 × 109 m
15. A certain radio programme is picked up at frequencies of 5 x 106 Hz in the short wave band and 100 MHz in the FM-band. Calculate the correspondingwavelengths.
𝑐 = 𝑓𝜆
3 × 108 = 5 × 106 × 𝜆
𝜆 = 60 𝑚
𝑐 = 𝑓𝜆
3 × 108 = 100 × 106 × 𝜆
𝜆 = 3 𝑚
Homework
p. 62,nos. 16, 17, 28, 29, 30, 31
16. Visible light ranges from red (λR = 670 nm) to violet (λV = 400 nm).Calculate the frequency of:
16.1 red light
16. Visible light ranges from red (λR = 670 nm) to violet (λV = 400 nm).Calculate the frequency of:
16.2 violet light
17.1 Calculate the frequency of a microwave with a wavelength of 5 cm.
17.2 An X-ray has a wavelength of 5 nm. What is the frequency of the X-ray?
28.1 Calculate the energy of a photon with a frequency of 3 x 108 Hz.
28.2 Calculate the energy of a photon with a frequency of 12 THz.
29.1 Calculate the energy of a photon with a wavelength of 660 nm.
29.2 Calculate the energy of a photon with a wavelength of 532 nm.
30.1 Calculate the wavelength of a photon with energy of 3,3 x 10-19 J.
30.2 Calculate the wavelength of a photon with energy of 5,4 x 10-19 J.
31.1 Calculate the frequency of a photon with energy of 1,33 x 10-17 J.
31.2 Calculate the frequency of a photon with energy of 9,93 x 10-10 J.