1.3- PHOTONS

Question 1

What type of radiation do all objects emit?

Answer 1

infrared radiation

Question 2

What do infrared cameras enable?

Answer 2

objects to be observed in darkness

Question 3

At what speed do all electromagnetic waves travel in a vacuum?

Answer 3

at the speed of light

Question 4

What is the speed of light?

Answer 4

3.00 * 10^8ms^-1

Question 5

Equation for wavelength

Answer 5

λ = v/f

wavelength = velocity/frequency

Question 6

In what measurement is light wavelengths often expressed in?

Answer 6

nanometres (nm)

Question 7

What is 1nm in metres?

Answer 7

1 nm = 0. 000 000 001m = 10^-9m

Question 8

Wavelength range for radio

Answer 8

> 0.1m

Question 9

Wavelength range for microwave

Answer 9

0.1m to 1mm

Question 10

Wavelength range for infrared

Answer 10

1mm to 700nm

Question 11

Wavelength for visible

Answer 11

700nm to 400nm

Question 12

Wavelength for ultraviolet

Answer 12

400nm to 1nm

Question 13

Wavelength for X-rays

Answer 13

100nm to 0.001 nm

Question 14

Wavelength for gamma rays

Answer 14

< 1nm

Question 15

What does an electromagnetic wave consist of?

Answer 15

an electric wave and a magnetic wave

Question 16

How does the electric wave and magnetic wave of an electromagnetic wave travel together and vibrate? (2)

Answer 16

at right angles to each other and to the direction in which they are travelling

in phase with each other. the two waves reach a peak together so they are in step. when they do this they’re said to be in phase

Question 17

From where is an electromagnetic waves emitted?

Answer 17

by a charged particle when it loses energy

Question 18

When can electromagnetic wave be emitted? (2)

Answer 18

a fast-moving electron is stopped (i.e. in X-ray tube) or slows down or changes direction

electron in shell of atom moves to different shell of lower energy

Question 19

How is an electromagnetic wave emitted?

Answer 19

as short bursts of waves

Question 20

How does each burst of EM wave leave from the source?

Answer 20

each burst leaves the source in a different direction

Question 21

What is each burst of EM wave?

Answer 21

a packet of electromagnetic waves

Question 22

What is each burst of EM wave referred to as?

Answer 22

photon

Question 23

Who and when was the photon theory established?

Answer 23

Einstein in 1905, when he used his ideas to explain the photoelectric effect

Question 24

What is the photoelectric effect?

Answer 24

emission of electrons from a metal surface when light is directed at the surface

Question 25

What did Einstein imagine photons to be like?

Answer 25

flying needles

Question 26

What did Einstein assume the energy E of a photon depend on?

Answer 26

its frequency f in accordance with the equation:

photon energy E = hf

Question 27

What is the h in the equation?

Answer 27

a constant referred to as the Planck constant

Question 28

What is the value of h?

Answer 28

6.63 *10^-34 Js

Question 29

What does a laser beam consist of?

Answer 29

photons of the same frequency

Question 30

What is the power of a laser beam?

Answer 30

energy per second transferred by the photons

Question 31

What is the formula for ‘the power of the beam’ ?

Answer 31

the power of the beam = nhf

n - number of photons in beam passing a fixed point each second