# physics revision

• Created by: annum
• Created on: 26-05-13 22:15

Life cycle of stars

-          Stars are formed from clouds of dust & gas

-          The Sun is at the stage of main sequence

-          A red super giant star eventually becomes a black hole

-          In a supernova gas & dust are thrown into space

-          Hydrogen turns into helium by nuclear fusion

-          Stars expand into red giant stars by larger nuclei are formed

-          Planets are formed by smaller amounts of gas & dust are pulled together

-          Red giant star becomes into a white dwarf

-          Nuclear fusion is nuclei joining

-          Our solar system contains heavier elements then helium because we are formed from a previous supernova

What is a wave?

·         A wave is a disturbance moving through a material (a medium)

·         The source of a wave is something that vibrates

·         TRANVERSE WAVE- a wave where the particles of a medium move at right angles to the direction in which the wave moves (water waves)

·         LONGITUDINAL WAVE- a wave where the particles vibrate in the same direction as the wave (imagine a slinky compressing)

·         Sound is a longitudinal wave; a sound source vibrates, causing compression pulses in the air nearby

·         Sound waves can travel through any gas, through liquids and solids

Describing waves

·         AMPLITUDE- The max. distance each point on a medium moves as a wave passes through it (in meters)

·         FREQUENCY- The number waves that pass every point in the medium every second (in Hz- 1Hz= 1 wave per second)

·         WAVE SPEED- The speed at which each wave crest passes through the medium (in m/s)

·         WAVELENGTH- The length of a complete wave, from crest to crest or place to place (in meters)

·         Amplitude and frequency depend on source, wave speed depends on medium

·         Wave speed (m/s) = Frequency (Hz) x Wave length (m)

Wave properties

·         Waves do not slow down as they travel- the wave speed in constant.

·         The wave loses amplitude as it travels due to friction

·         Reflection- When a wave hits a barrier, it bounces back off it. The angle of reflection (r) = the angle of incidence (i)

·         Refraction- The wavelength of a wave changes if they travel from a medium to another where their speed is different. If water waves go from a deep region to shallow, the wavelength is smaller

·         Diffraction- When waves hit the edge of a barrier or pass through a gap, they bend a little and spread out into the region behind the barrier

·         Interference- If 2 waves of the same frequency meet; they merge and form interference. Two waves that are "in step" produce a large disturbance, whereas 2 "out of step" waves cancel each other out

Bending light beams

·         Total internal reflection (TIR)