Week 8: Lecture (Light)

Today's lecture was on light. Light is a form of energy that is detected by the human eye. It can seem to behave like a wave in some conditions and like a stream of particles in other situations. Light is not like sound - it does not need a medium to travel through. This is why light can reach us from the sun despite space being a vacuum. 

Like water, light is a transverse wave. The vibrations are at right angles to the direction of motion from the source of the light. 

The visible light spectrum ranges from red to violet. Just outside of this spectrum is infrared and ultraviolet. If you go lower in frequency than infrared you get microwaves and radio waves, while going higher in frequency than ultraviolet there are x-rays and gamma rays.  

'White' light is made up of the entire visible spectrum. If you shine light into a glass prism it will refract and bend to show all the different colours. 

The velocity of light depends on the medium it is travelling through. In a vacuum it travels at 3*10⁸ m/s (or 300,000 km/s). It slows down slightly in air (but is still about 1 million times the speed of sound) and by about 2/3 in glass.