# P1 Revision 7

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• Created by: LBC0502
• Created on: 14-06-14 14:07
• P1 Revision
• Forming Images and Diffraction
• Diffraction is the spreading out of waves. Diffraction occurs when the wavelength is approximately the same size as the gap or obstacle (e.g.hill,building). Light is also diffracted by crystals.
• Refraction occurs when light travels across a boundary between mediums of different density. When moving into a material with a high density, the light slows down and changes direction towards the normal. When light is moving into a material with a lower density, the light speed up and changes direction away from the normal.(TAGAGA).
• Mirrors are virtual images. The image is the same size as the object and the same distance from the mirror as the object. Real: When light rays really come from a point. Virtual: When light rays seem to come from a point but they never actually met there.
• Reflection: (i) angle of incidence, (r) angle of reflection. The law of reflection states that the angle of incidence is always equal to the angle of reflection.
• The National Grid
• Step-up Transformer: Primary Power: P=IV, 100x10=1000W (less coils). Secondary Power: P=IV, 400x2.5=1000W (more coils). Step-Down Transformer: Primary Power: P=IV, 1000x2=2000W (more coils). Secondary Power: P=IV, 200x10=2000W (less coils).
• Power = Current x Voltage (P = IV)
• Largest surge in UK occurred after the solar eclipse 1999. Increase in electricity caused by: logging onto computers, starting up factories, switching on kettles. From 11:00-11:30, power surge after eclipse. Match demand: predict by using previous data from previous years, planned events, adverts in programmes etc.
• Step-up transformers: increases voltage, reduces current and reduces energy loss. Step-down transformers: decrease voltage for the consumer. Underground cables: more difficult to repair, much more expensive. Overhead cables: take up valuable land, more difficult to install across roads, railways and canals, spoil landscape, produce electric/magnetic fields that might affect people.
• Matching Supply with Demand: We have to match the supply of electricity to the demand of consumers: households, schools, businesses, transport and hospitals.On a graph, there will be a higher demand for electricity in the Winter than Summer and the peak would be during the evening.
• Parts of the national grid: power station (25kV), step-up transformer , over head/underground cables (132kV), step-down transformer, consumer. (Main supply in UK is 230V).
• Start up times (shortest - longest): hydroelectric, natural gas, coal, nuclear.
• Transverse and Longitudinal Waves
• Transverse waves vibrations are perpendicular (90 degrees) at wave motion. Oscillations are perpendicular to the direction of the wave motion e.g. water wave, light
• Longitudinal waves e.g. sound waves, mechanical waves on a spring, p seismic waves.
• Longitudinal waves have oscillations which are parallel to the energy transfer.
• Transverse waves e.g. water waves, light, em spectrum, x-rays, waves travelling along a spring, microwaves, L/R seismic waves.
• Both transverse and longitudinal waves are made up of oscillations (vibrations). They both transfer energy from one place to another. They both have peaks and troughs and they both have compressions and rarefactions.
• Waves
• A wave transfers energy from one place to another without transferring the medium (material:solid, liquid, gas) the wave is travelling through e.g. infrared waves.
• One oscillation (frequency - number of oscillation waves per second). Amplitude (m) - Maximum height og the wave measured from the middle (equilibrium). Wavelength (m) - Shortest distance between a point on a wave and the same point on the next wave. Frequency (Hz) - The number of waves passed a point per second.
• If the wavelength stays the same but the energy increased, then the amplitude will increase. As the frequency increases, the wavelength becomes shorter/decreases. kHz (kilo hertz = 1000Hz). MHz (mega hertz = 1,000,000Hz/1 x 106) 2MHz = 2 x 106 = 2,000,000 Hz. Waves travelling have a speed.
• Wave speed (m/s) = Frequency (Hz) x Wavelength (m). V = F x ?.
• A flute produces a not with a wavelength of 75cm. The speed of sound is 330m/s. Find the frequency of the note.V = 330m/s.  ? = 75cm = 0.75m. F = ?. F = V ÷ ?. F = 330 ÷ 0.75. F = 440Hz