GCSE PHYSICS SCIENCE A

Infrared radiation is energy transfer by electromagnetic waves.

All objects emit infrared radiation.

The hotter and object is the more I.R it emits in a given time.

The transfer of energy by I.R does not involve particles.

An object that is painted dull black will transfer energy and cool down quicker than the same object painted shiny white.

Dark,matt surfaces emit infrared radiation more quickly than light, shiny surfaces.

Light shiny surfaces reflect more infrared radiation than dark matt surfaces.

Dark matt surfaces absorb infrared radiation more quickly than light shiny surfaces.

An object painted dull black and left in the sun will become hotter than the same object painted shiny white.

FLOW,SHAPE,VOLUME & DENSITY are the properties used to describe each state of matter.

The particles in a solid are held next to each other, vibrating in their fixed position.They don't flow and the hotter it becomes the more they vibrate.

If you heat the solid it will eventually melt and become a liquid

The particles in a liquid move about at random and are in contact with each other. They will flow to fill the bottom of a container. Hotter a liquid gets the faster it  moves - makes it expand.

 If you now heat the liquid, eventually it will boil and become a gas.

The particles in a gas move about randomly. Much futher apart thatn particles in a solid or liquid. They don't keep a definate shape or volume and will fill any container. Hotter gas gets the faster it moves. Gases expand when heated or their pressure increases.

Conduction is the transfer of energy from particle to particle in matter.

If one end of a solid is heated, the particles at that end gain kinetic energy and vibrate more. This energy is passed to neighbouring particles and in this way the energy is transferred through the sold.

In addition, when metals are heated their free electroms gain kinetic energy and move through the meatal , transferring energy by colliding with other particles.

Materials that trap air are good insulators  because air is a poor conductor so materisals that trap air are good insulators.

Conduction in a metals is mainly due to free electrons transferring energy inside the metal.

When a fluid is heated it expands. The fluid becomes less dense and rises. The warm fluid is replaced by the cooler denser fluid. The resulting convection current transfers energy thorughout the fluid.

Convection is the circulation of a fluid caused by heating it.

All the particles in a liquid will have different amounts of energy. A liquid may evaporate even when it is below its boiling point. The faster molecules in a liquid have fores of attraction between them. The molecules have more kinetic ebergy and are able to  overcome this force and escape . After these molecules leave, the liquid is cooler because the average kinetic energy has decreased. THis is why ecaporation causes a cooling effect.

Evaporating is when a liquid turns into a gas.

The rate of evaporation is increased by increasing the surface area, increasing the temperature of a liquid and creating a draught of air across the liquids surface.

Condensation often takes place on cold surfaces such a windows and mirrors. IT is the change of state from a liquid to a gas.

CONDENSATION ON A MIRROR/GLASS

The gas on the mirror is cold and the air particles are warm and the water vapour hits the glass. The particles lose heat energy and form bonds and create a liquid and condense on the glass.

Why do clothes dry faster when they are spread out on the line on a sunny day with a breeze?

Because if they are spread out and have an increased surface area or if there is an increased temperature of liquid or there is a draught or it is windy over the surface area it makes the water evaporate faster. The water particles gain heat energy from the sun and escape.

Specific Heat Capacity Equation:

E= M X C X 0

Energy =  mass x SHC x temperature change

U- values tell us how much energy per second passes through different materials. The lower the u-value the better the material is as an insulator.

KINETIC ENERGY: Energy of a moving object due to its motion.

CHEMICAL ENERGY: Energy of an object due to chemical reactions in it.

ELECTRICAL ENERGY: Energy transferred by the movement of an electrical charge.

GRAVITATIONAL POTENTIAL ENERGY: Energy of an object due to its position in a gravitational field.

ELASTIC POTENTIAL ENERGY: Energy stored in an elastic object when work is done to change its shape.

Energy cannot be created or destroyed.

The total amount of energy is always the same. This is called the conservation of energy and applies to all energy transfer.

When an object falls, grav.pot energy is transferred to kinetic.

Stretching an elastic band transfers chemical energy to elastic potential energy.

In a solar cell, light energy is transferred to electrical energy,

Efficiency =

useful energy transferred by the appliance / total energy supplied to the appliance x 100

No machine can be more than 100% efficient

P = e/t

P = power in watts

E = energy in joules

T- Time taken (sec) for the energy to be transferred.

E = PxT

E= energy transferred in KWh

P= power of appliance in KW

T= time taken for energy to be transferred

Total cost = number of KWH x cost per KWh

In a pumped storage system surplus electricity is used, at times of low demand, to pump the water back up the hill to the top of the reservoir. This means that the energy is stored. Then at times of high demand the water can be released to fall through the turbines and transfer the stored energy to electrical energy.

At a hydroelectric power station, water is collected in a reservoir. This water is allowed to flow down hill and turn the turbines at the bottom of the hill.

Wave Power: We can use the movement of the waves on the sea to generate electricity. The movement drives a floating turbine that turns a generator. Then the electricity is delivered to the grid system on shore by a cable.

Tidal Power: The level of the sea around the coastline rises and falls twice each day. These changes in sea level are called tides. If a barrage is build across a river estuary, the water at each high tide can be trapped behind it. When the water is released to fall down to the lower sea level, it drives the turbines.

Geothermal energy is produced inside the earth by radioactive processes and this heats the surrounding rock. In volcanic or other suitable areas, very deep holes are drilled and cold water is pumped down to the hot rocks. There it is heated and comes back to the surface as steam. The steam is used to drive turbines that turn generators and so electricity is produced.

Solar energy from the sun travels through space to the Earth as electromagnetic raditation.

POWER STATION -->(25 kv) STEP-UP TRANSFORMER --> (132 kV or more) --> STEP-DOWN TRANSFORMER--> (230v) --> UNDERGROUND CABLE (HOMES)

In power stations, electricity is generated at a particular voltage. The voltage is increased by step-up transformers before the electricity is transmitted across the NG. This is because transmissions at a high voltage reduces the energy wated in the cables. making the system more efficient. It would be dangerous to supply electricity to consumers at these very high voltages. So, at local sub-stations, step-down transformers are used to reduce the voltage to 230v for use in homes and offices.

NATIONAL GRID: the network of cables and transformers used to transfer electricity from power stations to consumers.

TRANSVERSE WAVES

• Vibrate at right angles- perpendicular to the direction in which the wave travels.
• 

LONGITUDINAL WAVES

• The oscillation of the particles is parallel to the direction of travel of the wave.
• A longitudinal wave is made up of compressions and rarefactions

ELECTROMAGNETIC WAVES

• e.g light waves and radio waves
• can travel through a vacuum
• there are no particles moving in an electromagnetic wave as these waves are oscillations in electric and magnetic fields.
• the oscillations are perpendicular to the direction of travel of the wave.

MECHANICAL WAVES

• e.g waves on springs
• Travel through a medium (substance)
• May be transverse or longitudinal

AMPLITUDE: the height of the wave crest or the depth of the wave trough from the position at rest.

WAVELENGTH: The distance from one crest to the next crest, or from one trough to the next trough.

FREQUENCY: the number of wave crests passing a pont in one secons. The unit of frequency is the hertz (Hz). This unit is equivalent to per second.

WAVELENGTH = WAVESPEED / FREQUENCY

 FREQUENCY= WAVESPEED / WAVELENGTH

 WAVESPEED = FREQUENCY x WAVELENGTH

The angle of incidence is equal to the angle of reflection

A real image is one that can be formed on a screen, because the rays of light that produce the image actually pass through it.

A virtual image cannot be formed on a screen because the rays of light that produce the image only appear to pass through it.

The image in a plane mirror is: The same size as the object upright, The same distance behind the mirror as the object is in front and it is virtual.

Refraction of light is the change of direction of a light ray when it crosses a boundary between two transparent substances.

If the speed is increased, refraction is away from the normal (e.g glass into air)

If the speed is reduced, refraction is towards the normal (e.g air to glass)

Diffraction is the  spreading out of waves when they pass through a gap or round the wdge of an obstacle.

The narrower the gap the greater the diffraction.

SIGNAL PROBLEMS:

People living in hilly areas often have poor TV reception. The signal from a TV transmitter mast is carried by radio waves. If there are hills between a TV receiver and the transmitter mast, the signal may not reach the reciever. The radio waves passing the top of the hill are diffracted by the hill but they do not spread enough behind the hill.

• Radio waves - 10
•  Microwaces - 10
• infrared radiation - 10
• visible light - 10
• ultra violet - 10
• x-rays - 10
• gamma rays - 10

All EM waves travel through space at a wave speed of

300 million m/s

Microwave transmitters produce wavelengths that are able to pass through the atmosphere. They are used to send signals to and from satellites and within mobile phone networks.

The shorter the wavelength of the waves the more information they carry, the shorter their range, the less they spread out.

Radio waves are produced by applying an alternating voltage to an aerial

Research is needed to evaluate whether or not mobile phones are safe to use.... Scientists think the radiation from mobile phones may affect the brain.

OPTICAL FIBRES

Optical fibres are very thin glass fibres.

Optical fibres carrying visible light or infrared are useful in communications because they carry much more info and are more secure than radio and microwave transmissions.

We use them to transmit signals carried by visible light or infrared radiation. The signals travel down the fibre by repeated total internal reflection

DOPPLER EFFECT

" The change of wavelength and frequency of the waves from a moving source due to the motion of the source towards or away from the observer."

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

When the source moves away from the obserber, the observed wavelength increases and the frequency decreases.

RED SHIFT

 Increase in the wavelength of electromagnetic waves emitted by a start or galaxy due to its motion away from us. The faster the speed of the star or galaxy, the greater the red-shift is. 

CMBR

is electromagnetic radiation produced just after the 'big-bang'. At present it can only be explained by the 'big-bang' theory.

If the wavelength of CMBR is likely to change, if at all over the next billion years it will increase because the universe may continue to expand.

Red shift from distant galaxies provides evidence for the beginning of the universe because

• Red shift shows galaxies are moving away from the earth
• More distant galaxies are moving away faster
• The more distant galaxies show a greater red-shift

How energy is transferred from solar panels...

Heat energy from the sun hits the solar panel and heats the water in the pipes going through the hot water storage tanks. The water in the pipes Does not mix with the water from the boiler, so it goes round the pump circuit. The pump is to propell the water upwards and sometimes an extra boiler is needed to heat the water up.