Electromagnetic spectrum

Question 1

all electromagnetic waves…

Answer 1

are transverse

travel at the same speed in a vacuum or air
(3 x 10[8] m/s)

transfer energy to the observer as radiation

Question 2

electromagnetic spectrum

Answer 2

a continuous spectrum of waves split into seven distinct groups

range from waves with a short wavelength, high frequency and high energy to the opposite

from low to high:

• radio waves
• microwaves
• infared
• visible light
• ultraviolet
• x-rays
• gamma rays

radio waves have the lowest frequency and gamma rays have the highest

Question 3

speed of EM waves in air or a vacuum

Answer 3

3 x 10[8] m/s

300 000 000 m/s

Question 4

frequencies of visible light

Answer 4

red light has the lowest frequencies, violet light has the highest

the different groups all contain a range in frequencies

Question 5

What happens as the frequency of the radiation increases?

Answer 5

wavelength decreases

Question 6

approximate wavelengths of the different groups

Answer 6

(all in metres)

radio: 10[3] to <10[-2]
microwaves: around 10[-3]
infared: >10[-3] to 10[-6]
visible: 10[-6]
ultraviolet: 10[-7] to 10[-8]

x-rays: 10[-8] to 10[-11]

gamma rays: 10[-10] to 10[-12]

(NOT frequencies or speeds)

Question 7

a) List the main groups of electromagnetic waves from longest to shortest wavelength [1]
b) Calculate the frequency of an electromagnetic wave travelling in air that has a wavelength of 5x10[-7]m [4]

Answer 7

a) radio, microwave, infared, visible, ultraviolet, x-rays, gamma
b) f = v / wavelength

f = 3 x 10[8] / 5 x 10[-7]
= 6 x 10[14] Hz

Question 8

State the type of electromagnetic radiation that has the (a) longest wavelength, (b) highest frequency. [2]

Answer 8

a) radio waves

b) gamma rays

Question 9

The human eye detects wavelengths that range from 4 x 10[-7] m to 7 x 10[-7].

Work out the range of frequencies that the human eye detects. [3]

Answer 9

4 x 10[-7]m:
f = v / wavelength = 7.5 x 10[14] Hz

7 x 10[-7] m:
4.3 x 10[14]Hz

Question 10

An electromagnetic source produces 4 x 10[18] waves in 1 minute.

a) Calculate the wavelength of the source [3]
b) State what part of the electromagnetic spectrum this radiation belongs to [1]

Answer 10

a) frequency: 4 x 10[18] / 60 = 6.7 x 10[16] Hz
wavelength: 3 x 10[8] / 6.7 x 10[16] = 4.5 x 10[-9] m
b) x-rays