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)…
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