(AQA) GCSE Physics - P1 Unit 1 whole revision

Infrared radiation (IR)

• IR is energy transfer by electromagnetic waves.
• All objects emit IR.
• The hotter the obejct the more IR it emited.

Surfaces and radiation

• Dark, matt surfaces emit and absorb IR more quickly than light, shiny surfaces.
• Light shiny surfaces reflect more IR than dark, matt surfaces.

States of matter

• Flow, shape, volume and density are the properties used to describe each state of matter.
• The three states of matter are solid, liquid and gas.
• In a solid, the particles are held together vibrating in their fixed positions.
• In a liquid, the particles move around and are in contact with each other.
• In a gas, the particles move freely as they do not have a shape and can flow.

Conduction

• Occurs mainly in solids.
• Metals are the best conductors because they have free electrons transferring energy inside the metal. Unlike non-metals which dont.
• Poor conductors are called insulators, materials such as wool and fibreglass are good insulators because they contain trapped air.

Convection

• Occurs in fluids like liquids and gases.
• Heating a liquid/gas makes it less dense so it rises and causes circulation.

Evaporation and Condensation

• Evaporation is when a liquid turns to gas, this can be increased by increasing surface and temperature.
• Condensation is when gas turns to liquid, this can be increased by increasing surface area and decreasing the surface temperature.

Energy transfer by design

The rate of energy transfer to or from an object depend on:

• The shape,size and type of material of the object.
• The materials that the object is in contact with.
• The temperature difference between the object and its surroundings.

Flask (An often used example in exams)

• Plastic cap
• Double-walled glass (or plastic) container
• Plastic protective cover
• Hot or cold liquid
• Sponge pad (for protection)
• Inside surfaces silvered to stop IR
• Vacuum prevents conduction and convection

Specific heat capacity (SHC)

• The greater the mass of an object, the more slowly its temperature increases when it is being heated.
• The rate of temperature change in a substance when heated depends on the energy transferred, mass and SHC.

Equation for Specific Heat Capacity:

E = m x c x θ

• E = Energy transfered (J)
• m = mass (kg)
• c = shc (J/kg'c)
• θ = temperature change ('c)

Heating and insulating buildings

Most people want to minimise the rate of energy transfer out of their homes to reduce fuel bills, this can be done by doing the following:

• Fibreglass loft insulation (reduce conduction)
• Cavity wall insulation (reduce convection)
• Double glazing (reduce conduction through windows)
• Draught proofing (reduce convection)
• Aluminium foil behind radiators to reflect IR back into the room.
• Solar heating panels

U-value: tells us how much energy per second passes through materials, the lower the U-value the better the material is as an insulator.

Types of energy:

• Light, sound, kinetic(movement), nuclear, electrical, gravitational potential, elastic potential and chemical.
• Energy cannot be created or destroyed.

Useful energy: energy that is transferred to the place we want and in the form we want it.

Wasted energy: energy which is not usefully transferred.

Efficiency = useful power obtained x100%

                  total power supplied

• No machine can be more than 100% efficient, if your answer is more than 100 you have done the calculations wrong.
• The make machines more efficient you can reduce friction, air resistance and electrical resistance.
• The energy transfer through an appliance can be drawn using a sankey diagram.

• Power is a rate of transfer of energy.

• P = Power (W) = watts
• E = Energy (J) = joules
• t = Time taken (s) = seconds

 Efficiency =

Cost effectiveness: Getting the best value for money.

Total cost of electricity used = energy used in kWh x cost of 1 kWh (1 unit).  (LEARN)

Look out for cost in pence and pounds and convert if necessary!

The payback time is the time it takes for an appliance or installiation to for itself in terms of energy savings.

Pay back time (in years) = cost of installation ÷ saving per year  (LEARN)

Fuel for electricity

• Electricity generators in power stations are driven by turbines.
• Coal, oil and natural gas are burned in fossil-fuel power stations.
• Nuclear power stations used either uranium or plutonium.
• Biofuels are renewable sources of energy which can generate electricity.

Energy from wind and water

• Energy can obtained from wind, waves and tides (this is renewable)
• Wind turbines are renewable energy source. (renewable)
• Hydroelectric generators are turned by water running downhill. (renewable)
• Tidal power station traps high tides and uses them to turn generators.

Power from the Sun and Earth

• Solar cells transfer solar energy directly into electricity.
• Solar heating panels can use the Sun's energy to heat water directly.
• Geothermal energy comes from inside the Earth.

Energy and the environment

Coal, Oil & Gas (non-renewable)

• Produce carbon dioxide, and sulphar dioxide which can cause acid rain (gas doesnt do this)
• Reliable

Nuclear Energy (non-renewable)

• Produces hazardous nuclear waste, which is difficult to dispose of safely.
• Small risk of a big nuclear accident.

Wind, Waves, Tides, Solar & Geothermal (renewable)

• Not very reliable
• Waves - can be a danger to boats.
• Free source of energy
• Solar - Unreliable in less sunny countries.

National Grid: distributes electricity from power stations to our home.

• Step-up and Step-down transformers are used in the National Grid.

Step-up transformer: Increases the voltage before it is transmitted across the National Grid, this is because at a high voltage it reduces the energy wasted in cables making the system more efficient.

Step-down transformer: Decreases the voltage so that it is suitable for our homes at 230V.

Transverse waves: Vibrate at right angles to the direction of energy transfer. All electromagnetic waves are transverse.

Longitudinal waves: Vibrate parallel to the direction of energy transfer. A sound wave is longitudinal.

Mechanical waves: Needs a medium susbstance. May be transverse or longitudinal.

V = f x λ

v = Speed (m/s)

f = frequency (Hz)

λ = wavelength (m)

• The red line is called the Normal.
• The laws of reflection state that: The angle of incidence is equal to the angle of reflection.

• In this case, the normal line is not red it is the greyish line.
• Refraction of light is the change of direction of a light ray when it crosses a boundary between two transparent substances.
• If speed is reduced, refraction is towards the normal.
• If speed is increased, refraction is away from the normal.

• Diffraction is the spreading out of waves when they pass through a gap or round the edge of an obstacle.
• The narrower the gap, the greater the diffraction.

The electromagnetic spectrum (in order of decreasing wavelenght) is:

• Radio, Microwaves, Infrared, Light, Utraviolet, X-rays and Gamma radiation.

If you are struggling to remember them then you could remember the first letter of each wave and replace it for something you know or turn it into a sentence.

E.g. Raging Martians Invaded Venus Using X-ray Guns

or Roman Men Invented Very Unusual X-ray Guns

* Questions about the electromagnetic spectrum often come up in exams, you may even be asked to put them in increasing or decreasing order.

• Microowaves are used for satellite TV signals.
• Optical fibres are very thin fibres that are used to transmit signals by light and IR.

Expanding Universe

Red-shift: Light from distant galaxies is red-shifted. The faster the speed of the star or galaxy, the greater the red-shift is. Red-shift provides evidence that the universe is expanding.

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

• The universe started with the Big Bang: a massive explosion from a very small initial point.
• The universe has been expanding ever since the Big Bang.
• Cosmic Microwave Background Radiation (CMBR) is electromagnectic radiation created just after the Big Bang.
• The Big Bang Theory is so far the only explanation for why this is here.

E = m × c × θ

Efficiency =

Efficiency =

E = P x t

v = f × λ