Electromagnetic Waves
What are they? #
Coupled electric and magnetic oscillations that move with the speed of light and exhibit typical wave behavior.
The story #
- Faraday: Changing magnetic field can induce a current in a wire loop
- James Clerk Maxwell: Accelerated electric charges/changing electric field generate linked electric and magnetic fields.
- Based on symmetry argument but not on experimental findings as they are harder to detect.
- Concluded that light consists of electromagnetic waves
- Heinrich Hertz: Showed that EM waves do exist. ^6e61b3
- Conducted an experiment with two metal balls
- Generated waves by applying alternating current to an air gap between those balls.
- A wire loop with a small gap was the detector=> em waves set up oscillations in the loop that produced sparks in the gap.
Waves #
Range of visible light: $[4.3\rightarrow7.5]*10^{14} Hz$
Principle of Superposition: When two or more waves of the same nature travel past a point at the same time, the instantaneous amplitude there, is the sum of the instantaneous amplitudes of the individual waves.
Instantaneous Amplitude #
Displacement from mean position. Since electric and magnetic fields in a light wave are related by $\frac{E}{B}=c$, its instantaneous amplitude can be taken as either E or B but usually E is used
Young’s experiment #
He used a pair of slits illuminated by monochromatic light from a single source and demonstrated interference of light waves.
Places on the screen where path length difference is
- odd number of half wavelengths: destructive interference
- even number of half wavelengths: constructive interference