# Physics

HideShow resource information

## Conduction & Convection

Condution

The atoms/particles vibrate more in high temperature than low temperature. They hit each other sending energy. Because the electrons are free to move they can pass energy much faster

Convection

Convection currents happen in liquids, because the particles move faster. This enables the particles to move away from each other and causes the liquid or gas to expand becoming less dense. Less dense liquids rise up

1 of 31

## Kinetic theory of matter

SolidLiquidGas Arrangement of particles

close together

regular pattern

close together random

far apart

random

movement of particles vibrate about a fixed position move around each other move quickly in any direction diagram

2 of 31

## Evaporation

The particles in a liquid have different energies. Some will have enough energy to escape from the liquid and become a gas. The remaining particles in the liquid have a lower average kinetic energy than before, so the liquid cools down as evaporation happens. This is why sweating cools you down. The sweat absorbs energy from your skin so that it can continue to evaporate

## Condensation

The particles in a gas have different energies. Some may not have enough energy to remain as separate particles, particularly if the gas is cooled down. They come close together and bonds form between them. Energy is released when this happens. This is why steam touching your skin can cause scalds: not only is the steam hot, but energy is released into your skin as the steam condenses

3 of 31

Absorbs best Dull black Emits best

Shiny black

White

Absorbs worst  Silver  Emits worst

4 of 31

## Specific heat capacity

Specific heat capacity - amount of energy it takes to heat something up

Specific heat capacity = energy input

mass = temperature x rise

5 of 31

## Energy transfer & efficiency

Kinetic

Graviational potential

Elastic strain

Heat

Light

Sound

Electrical

Chemical

Nuclear

6 of 31

Solar

Tidal

Waves

Hydroelectric

Wind

Fossil fuels -

Coal

Oil

Geothermal

Biomass (food)

7 of 31

## Notes on unit 1.1 & 1.2

Diffusion - When smell spreads out across a room

Thermal radiation - The transfer of energy by electromagnetic waves

U-values - Measure how effective a material is as an insulator. The lower the u-value the better the material is at insulating

Energy cannot be created or destroyed

Friction - Energy is often wasted as heat losses caused by the force of friction. Friction can be reduced by lubrication and streamlining

8 of 31

## Changes of state

9 of 31

1. The stopper reduces energy transfer by convection, gases cannot rise or sink past the stopper  2. The vacuum reduces energy transfer by conduction and convection, there are no particles to transfer the energy   3. The silvery surfaces reduce energy transfer by radiation, reflecting back the energy

10 of 31

## Power

Power = energy transferred

time taken

11 of 31

## Generating electricity

A typical power station

Boiler -> Turbine -> Generator -> National grid

Boiler - An energy source is used to heat water - Chemical energy to heat energy

Turbine - The steam produced drives a turbine - Heat energy to kinetic energy

Generator - A tubine that is coupled to an electric generator - Kinetic energy to electrical energy

12 of 31

## Alternative Energy

There are a number of alternative sources of energy...

Wind  Tides  Geothermal

Waves  Sun  Biomass

Hydroelecric dams

These sources are renewable

Wind and water can be used to drive turbines directly

13 of 31

## Alternative Energy sources

Solar, wind, tidal, waves, hydroelectric, geothermal, biomass - water related

Convection current - Air is heated by the sun and rises off the equator. Cooler air moves in, moving air = wind

14 of 31

## The National Grid

Power station -> Tranformer (step up) -> Transmission -> Transformer (step down) -> transmission -> transmission -> transformer (step down) -> transformer (step down) -> transformer (step down)  -> Schools, homes, offices and shops

Step up voltage - reduces current

Less current - wires not so hot - less energy wasted

Step down voltage - safe to use

15 of 31

## Waves

Waves transfer energy without any matter being transferred

Wavelength - the distance between a particular point on one wave and the same point on the next wave

Amplitude - the maximum disturbance caused by a wave

Frequency - the number of waves passing each second, measured in hertz, Hz

Wavespeed = frequency x wavelength

metre/second hertz metre

m/s hz m

16 of 31

## Longitudinal waves

Example - sound waves travel through solids, liquids and gases as longitudinal waves

17 of 31

18 of 31

## Reflection

Light from the sun reflects off the tree and into our eyes

Types of relfection -

Normal reflection occurs at smooth surfaces like the water and produces an image

Diffuse reflection occurs at rough surfaces like the building and the light is scattered

19 of 31

## Reflection (Part 2)

A flat mirror is called a plane mirror. We always measure angles from the normal

20 of 31

## Notes

Angle of incidence - the angle between the incident ray and the normal

Angle of reflection - the angle between the reflected ray and the normal

Law of reflection - angle of incidence is equal to the angle of reflection

Real and virtual images - rays of light pass through a real image but only appear to come through a virtual image

21 of 31

## Refraction

Rays of light change direction (are refracted) when they cross the boundary between one transparent medium and another, unless they meet the boundary at a right angle. Waves are not refracted if travelling along the normal

22 of 31

## Diffraction

When a wave moves through a gap, or past an obstacle, it spreads out from the edges

Straight waves are called plane waves

If the gap is a similair size to the wavelength, the diffraction is more significant

Waves having a longer wavelength are more strongly diffracted

23 of 31

## Sound

Sound doesn't travel through a vacuum

Sounds result when objects vibrate

Soundwaves are longitudinal waves and cause vibrations in a medium (material), a series of compressors and rarefactions

Humans can hear sounds in the range of 20Hz to 20000Hz

Infrasound - sound lower than humans can hear

Ultrasound - sound louder than humans can hear

Sound waves are shown on an oscrilloscope

The pitch of a sound is determined by it's frequency. The higher the number of vibrations the higher the pitch

The pitch of a sound is determined by it's loudness by it's amplitude. The greater the size of the vibrations, the louder the sound

24 of 31

## Electromagnetic spectrum

25 of 31

the shorter their range in air - due to their increasing absorption in the  air

The less spread out, the less diffraction

less than 1m - tv from terrestrial masts, the waves can carry more information

between 1m & 100m - local radio and emergency services

greater than 100m - national and international radio stations

26 of 31

## Microwaves

Microwave radiation can pass through the earth's atmosphere to and from satellites. Microwave signals do not spread out or waken as much as radio signals

27 of 31

Mobile phone networks also send and receive information using microwaves. The mobile phone sends a signal to the mast which is then routed through the phone network to the receiving phone. The return is routed through the mast to the sending phone. The signals to and from the mast are carried by radio waves of different frequencies

28 of 31

## Microwaves and Infra-red

Microwave waves are positive and negative which flips the water molecules and makes them hotter which cooks the food

All objects emit infrared radiation. The hotter the object, the more infrared radiation it emits. Infrared radiation is absorbed by the skin, heating it up. It can damage or kill skin cells

29 of 31

## Fibre optic

The light is reflecting off the insides of the optical fibre which we call total internal relfection. By flashing the light off and on you can send messages/signals

30 of 31

## Red shift & the Doppler effect

When an object moves away from an observer, its light is affected by the Doppler effect

# The Doppler effect

You may have noticed that when an ambulance or police car goes past, its siren is high-pitched as it comes towards you, then becomes low-pitched as it goes away. This effect, where there is a change in frequency and wavelength, is called the Doppler effect.

When a source moves towards an observer, the observed wavelength decreases and the frequency increases.

When a source moves away from an observer, the observed wavelength increases and the frequency decreases.

31 of 31