Photons Flashcards
Electromagnetic waves consist of an:
electric wave and a magnetic wave which travel together and vibrate:
- 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 two waves are like this we can say they are in phase.
What emits electromagnetic waves?
- Electromagnetic waves are emitted by a charged particle when it loses energy.
- This can happen when
- a fast-moving electron is stopped (for example, in an X-ray tube) or slows down or changes direction.
- An electron in a shell of an atom moves to a different shell of lower energy.
How are electromagnetic waves emitted?
Electromagnetic waves are emitted as short bursts of waves, each burst leaving the source in a different direction. Each burst is a packet of electromagnetic waves and is referred to as a photon.
How did Einstein imagine photons?
Einstein imagined photons to be like flying needles, and he assumed that the energy E of a photon depends on its frequency f in accordance with the equation.
photon energy E = hf
Planck’s constant
6.63 x 10-34 J s
What does a laser beam consist of?
A laser beam consists of photons of the same frequency. The power of a laser beam is energy per second transferred by the photons. For a beam consisting of photons of frequency f.
Wavelength formula
the power of the beam eq.
the power of beam = nhf
n = no. of photons
hf = energy of each photon
nhf = power/energy per second
Wavelength range of radio waves
More than .1 m
Wavelength range of microwaves
1mm - .1m
Wavelength range of infrared
1 mm - 700nm
Wavelength range of visible light
400nm - 700nm
Wavelength range of ultraviolet
1nm - 400nm
Wavelength range of X-rays
.001nm - 10nm
Wavelength range of gamma rays
Less than 1 nm
