1.3- PHOTONS Flashcards
What type of radiation do all objects emit?
infrared radiation
What do infrared cameras enable?
objects to be observed in darkness
At what speed do all electromagnetic waves travel in a vacuum?
at the speed of light
What is the speed of light?
3.00 * 10^8ms^-1
Equation for wavelength
λ = v/f
wavelength = velocity/frequency
In what measurement is light wavelengths often expressed in?
nanometres (nm)
What is 1nm in metres?
1 nm = 0. 000 000 001m = 10^-9m
Wavelength range for radio
> 0.1m
Wavelength range for microwave
0.1m to 1mm
Wavelength range for infrared
1mm to 700nm
Wavelength for visible
700nm to 400nm
Wavelength for ultraviolet
400nm to 1nm
Wavelength for X-rays
100nm to 0.001 nm
Wavelength for gamma rays
< 1nm
What does an electromagnetic wave consist of?
an electric wave and a magnetic wave
How does the electric wave and magnetic wave of an electromagnetic wave travel together and vibrate? (2)
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
From where is an electromagnetic waves emitted?
by a charged particle when it loses energy
When can electromagnetic wave be emitted? (2)
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
How is an electromagnetic wave emitted?
as short bursts of waves
How does each burst of EM wave leave from the source?
each burst leaves the source in a different direction
What is each burst of EM wave?
a packet of electromagnetic waves
What is each burst of EM wave referred to as?
photon
Who and when was the photon theory established?
Einstein in 1905, when he used his ideas to explain the photoelectric effect
What is the photoelectric effect?
emission of electrons from a metal surface when light is directed at the surface
