M7 Topic 1 Part1: Electromagnetic Spectrum - What is Light Flashcards
who contributed to classical theory of electromagnetism
James Maxwell
what are Maxwell’s contributions to the classical theory of electromagnetism (3)
- Unified electricity and magnetism
- Prediction of Electromagnetic waves
- Predicted the speed of light
What did Maxwell predict about electricity and magnetism.
That they form a self propagating electromagnetic wave with an oscillating electric and magnetic field.
what did maxwell predict about electromagnetic waves.
Visible light is apart of the electromagnetic spectrum and is only a small part of the em spectrum
What did Maxwell predict about the speed of light.
Through the use of preconcieved physics laws (Gauss,Faraday,Ampere) (1/√με= c) calculated the speed of light to be = 3x10^8
what makes a electromagnetic waves (3)
- moving charged particles have a changing electrical field creating a magnetic field
- a Varying magnetic field will give rise to an electric field
- The fields propagate in phase with each other at right angles
What methods were/can be used to calculate the speed of light (3)
- Roemer’s method
- Fizeau’s Method
- Microwave
What was Roemer’s method for calculating speed of light and what value did he get
Roemer measured the speed of light by timing eclipses of Jupiter’s moon Io. which has to travel an extra distance represented by the diameter of the Earth’s orbit. approx 210000 km/s
What and when was Fizeau’s method for calculating speed of light
he shone an intense light source at a mirror 8km away and broke up the the light beam with the rotating cogwheel until the reflected light beam could no longer be seen returning through the gaps 298,000 km/s
how do you use a microwave method for calculating speed of light
use the equation v=fλ
f-frequency on the back of the microwave
λ-wavelength, use foodie cheese to measure adjacent hotspots which show the value for half wave length
who verified Maxwell’s predictions
Heinrich Hertz
How did Heinrich Hertz explain the sparks he got from his experiment
stated the EM waves caused by accelerating charged particles during the discharge and the secondary loop created a large enough potential difference to create a spark
How did Hertz radio waves behave (2)
- They were polarised, and could only produce sparks when the coil was in a specific orientation
- The waves would reflect, He bounced them off a zinc plate toward a receiver which would spark
How did Hertz calculate the speed of radio waves.
Hertz used reflection to make a standing wave pattern, and found places where the loop sparked to find two adjacent antinodes to find the half wavelength,allowing him to calculate the velocity of the wave , and verify maxwell’s predictions
What allows light to define the metre (2)
- The speed of light in a vacuum is a universal constant
- Independant of the observer’s frame of reference
