1.3 Photons

Question 1

What do all electromagnetic waves do in a vacuum?

Answer 1

» Travel at the speed of light

Question 2

What is the speed of light?

Answer 2

» 3.00 x 10^8 ms^-1

Question 3

What is the formula for the wavelength of an electromagnetic wave?

Answer 3

» Wavelength = speed of light/frequency

Question 4

What are the main parts of the electromagnetic spectrum?

Answer 4

» Radio waves => 0.1m

»  Microwaves 0.1m to 1mm

» Infrared 1mm to 700nm

» Visible 700nm to 400nm

» Ultraviolet 400nm to 1nm

» X-rays 10nm to 0.001nm

» Gamma rays < 1nm

Question 5

What is an electromagnetic wave?

Answer 5

» Consists of an electric wave and a magnetic wave which travel together and vibrate

Question 6

What are the 3 features of an electromagnetic wave?

Answer 6

» At right angles to each other

» In phase with each other

» When 2 waves reach a peak together so they are in step - phase

Question 7

When are electromagnetic waves emitted?

Answer 7

» A fast-moving electron is stopped or slows downs or changes direction

» An electron in a shell of an atom moves to a different shell or lower energy level

» Electromagnetic waves are emitted as short burst of waves, each burst leaving the source in a different direction

Question 8

What is a photon?

Answer 8

» Each burst is a packet of electromagnetic waves

Question 9

What is the photoelectric effect?

Answer 9

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

Question 10

What is the photon energy equal to?

Answer 10

» E = hf

Question 11

What is h?

Answer 11

» Referred to Planck constant
» Value of 6.63 x 10^-34

Question 12

What did Einstein assume?

Answer 12

» That the energy of a photon depends on its frequency in accordance with the equation E= hf

Question 13

What does a laser beam consist of ?

Answer 13

» A laser beam consists of photons of the same frequency

Question 14

What does the power of a laser depend on?

Answer 14

» The energy per second transferred by the photon

Question 15

What is the equation of the power of a laser beam?

Answer 15

» Power of the beam = nhf

Question 16

» What is n in the power of the beam equation?

Answer 16

» Where n is the number of photons in the beam passing a fixed point each second

» This is because each photo has energy hf. Therefore, if n photons pass a fixed point each second the energy per second is nhf