1.3 - Photons Flashcards
What speed do electromagnetic waves travel in a vacuum
The speed of light (c)
3.00 x 10^8
How do you find the wave length of electromagnetic radiation
Wavelength = speed of light / frequency
Radiowave wavelength
> 0.1m
Microwave wavelength
0.1 m to 1mm
Infrared radiation wavelength
1mm to 700nm
Visible light wavelength
700nm to 400nm
Ultraviolet wavelength
400nm to 1nm
X-ray wavelength
10nm to 0.001nm
Gamma ray wavelength
<1nm
What does an electromagnetic wave consist of
Electric wave and magnetic wave that travel together and vibrate at right angles to each other and to the direction they are travelling
They also vibrate in phase with eachother (the waves reach a peak together)
What are electromagnetic waves emitted by
Charged particles when they lose energy
When is an electromagnetic wave emitted
- When a fast moving electron is stopped (for example in an X-ray tube) or slows down or changes direction
- when an electron in a shell of an atom moves to a different shell of lower energy
What are electromagnetic waves 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
What is a photon
A packet of electromagnetic waves
Who was the photon theory explained by
Einstein in 1905 when he used his ideas to explain the photoelectric effect
What is the photo electric effect
The emission of electrons from a metal surface when light is directed at the surface
What is the equation to find out photon energy
E =hf
Where h is Planck constant
And f is frequency
What is Planck constant
6.63x10^-34 Js
What does a laser beam consist of
Photons of the same frequency
What is the power of a laser beam
The energy per second transferred by the photons
The power of the beam =
nhf
Where n is the number of photons passing through a fixed point each second
Hf because each photon has energy
