Physics Unit 1(Core)

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  • Created by: Elaine
  • Created on: 08-06-13 14:17

1.1 Infrared radiation

Infrared radiation is energy transfer by electromagnetic waves, we can detect infrared radiation with our skin - it makes us feel warm.

All objects emits (gives off) infrared radiation.

The hotter an object is the more infrared radiation it emits in a given time.

Infrared radiation can travel through a vacuum, this is how we get energy from the sun.

The transfer of energy by infrared radiation does not involve particles

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1.2 Surfaces and radiation

Dark, matt surfaces are better absorbers of infrared radiation than light, shiny surfaces - absorbs radiation more quickly.

Dark, matt surfaces are better emitters of infrared radiation than light, shiny surfaces - emits radiation more quickly.

Light, shiny surfaces are good reflectors of infrared radiaition - reflects more radiation than dark, matt surfaces

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1.3 States of matter

Three states of matter are solid, liquid and gas. Substance can change between these states by heating or cooling it.

Flow, shape, voloume and density are the properties used to describe each state of matter.

Particles in a solid are held next to each other, vibrating in their fixed positions, so solids has a fixed shape.

Particles in a liquid move about at random and are in contact with each other, so liquids doesn't have a fixed shape and can flow.

Particles in a gas move aout randomly and are much farther apart than particles in a solid or liquid, so gases doesn't have a fixed shape and can flow.

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1.4 Conduction

Conduction occurs mainly in solids. Most liquisa and all gases are poor conductors.

If one end of a solid is heated, particles at that end gain kinetic energy and vibrate more. The energy are passed on to neighboring particles and the energy are transferred through the solid. 

Metals are the best conductors. Conduction in a metal is mainly due  to free electrons transferring the energy inside the metal - free electrons gain kinetic energy and move through the metal, transferring energy by colliding with other particles.

Non-metals are poor conductrs because they do not contain free electrons.

Poor conductors are called insulators, materials such as wool and fibreglass are good insulators.

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1.5 Convection

Convection occurs in fluids (liquids and gases).

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

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

Convection cannot occur in solids.

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1.6 Evaporation and condensation

Evaporation is when a liquid turns into a gas.

Takes place when most energetic liquid molecules escape from the liquid's surface and enter the air. Therefore, the average kinetic energy of the remaining molecules is less, so temperature of the liquid decreases - causes cooling.

Rate increases by;
- increasing the surface area
- increasing the temperature
- creasting a draught

Condensation is when a gas turns into a liquid.

Takes place on cold surfaces such as windows and mirrors.

Rate increases by;
- increasing the surface area
- reducing the surface temperature 

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1.7 Energy transfer by design

The rate of energy transfer to or from an object depends on;
- the shape, size and type of material of the object
- the materials the object is in contact with
- the temperature difference between the object and its surrounding 

The greater the temperature difference between an object and its surrounding, greater the rate at which energy transfer.

To maximise the rate of energy to keep things cool, use things that;
-  are good conductors
- are painted dull black
- have the air flow around them maximised

To minimise the rate of energy to keep things warm, use things that;
- are good insulators
- are white and shiny
- prevent convection currents by trapping air in small pockets 

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1.8 Specific heat capacity

Specific heat capacity of a substance is the amount of energy required to raise the temperature of 1kg of the substance by 1 degree celcius.

The greater the specific heat capacity, the more energy required for each degree temperature change.

The greater the mass of an object, the more slowly its temperature increases when it is heated.

The rate of temperature change in a substance when heated depends on the energy transferred to it, its mass and its specific heat capacity

Equation for specific heat capacity is:    E = m × c × θ

E is energy transferred, J
m is mass, kg
c is specific heat capacity, J/kg°C
θ is temperature change, °C

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1.9 Heating and insulating buildings

The rate of energy transfer to or from our homes can be reduced. Done by fitting;
- fibreglass loft insulaion --> reduce energy transfer by conduction 
- cavity wall insulation --> traps air in small pockets to reduce energy transfer by convection
- double glazing --> reduce energy by conduction through windows
- draught proofing --> reduce energy transfer by convection
- aluminium foil --> behind radiatprs to reflect radiation becak into the room

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.

Solar heating panels do not use fuel to heat water but they are expensive to buy and install. 

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2.1 Forms of energy

Energy exist in different forms such as;
- light
- sound
- kinetic (movement)
- nuclear
- electrical
- gravitational potential
- elastic potential
- chemical 

Energy can be transferred from one form into another form.

When an object falles and gains speed, its gravitational potential energy decreases and its kinetic energy increases.

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2.2 Conservation of energy

Energy cannot be destroyed or create - only possible to transfer it from one form into another, or from one place to another.

Means the total amount of energy is always the same. Called the conservation of energy and it applies to all energy transfers.

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2.3 Useful energy

Machine is something that transfer energy from one place to another or from one form to another.

Energy we get out of machine consist of;
- useful energy, which is transferred to the pace we want and in the form we want it
- wasted energy, which is not usefully transferred

Useful energy and wasted energy both end up being transferred to the surroundings, which becomes warmer where the energy becomes too difficult to be use for further energy transfers.

Energy is often wasted due to friction between the moving parts of a machine. The energy warms the machine and the surroundings.

Sometimes wasted energy is transferred as sound, but the amount of energy is usually very small eventually transferred to the surroundings making them warmer. 

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2.4 Energy and efficiency

Energy supplied to a machine is called input energy.
input energy (energy supplied) = useful energy transferred + energy wasted

The less energy that is wasted by a machine, the more efficient the machine. 

Equation to calculate the efficiency of any appliance;
Efficiency = (useful energy transferred ÷  total energy supplied) x 100 
Efficiency is a ratio. Does not have a unit!!! 

No machine can be more than 100% efficient! ... except an electric heater
Measures  to make machines more efficient include reducing;
- friction
- air resistance 
- electrical resestance
- noise due to vibrations

The energy transfer through an appliance can be represented with a Sankey diagram. 

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3.1 Electrical appliances

Electrial appliances can transfer electrical energy into useful energy at the flick of a switch.

Uses of everyday electrical appliances include heating, lighting, making objects move and creating sound and visual images.

An electrical appliance is designed for a particular purpose and should waste as little energy as possible.

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3.2 Electrical power

Power is rate of transfer of energy.

Equation for power is;

P = E ÷ t

P is the power in watts, W
E is the energy in joules, J
t is the time taken in seconds, s

Efficiency = (useful energy ÷ total energy) x 100

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3.3 Using electrical energy

Kilowatt-hour (kWh) is the energy supplied to a 1kW appliances in 1 hour.

Equation to find the amount of energy transferred to a mains appliance;

E = P x t

E is the energy tranferred in kilowatt-hour, kWh
P is the power of the appliance in kilowatt, kW
t is the time taken in seconds, s

Electricity meter in a house records the number of kWh of energy used. If the previous meter reading is subtracted from current reading, electrical energy used between the reading can be calculated.

Equation to find cost of the electrical energy;

total cost = number of kWh x cost per kWh

The cost per kWh is given on the electricity bill. 

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3.4 Cost effectiveness matters

Cost effectiveness means getting the best value for money, must be considers with a number of different costs.

May include for comparison;
- the cost of buying the appliance
- the cost of installing the appliance
- the running costs
- the maintanence costs
- environmental costs
- the interest charged on a loan to buy the appliance

Payback time is the time it takes for an appliance or installation to pay for itself in terms of energy savings

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4.1 Fuel for electricity

In power stations, water is heated to produce steam. The steam drives a turbine, which is coupled to an electrical generator that produces the electricity.

Coal, oil and natural gas are burned in fossil-fuel power stations - fossil fuels are obtained from long-dead biological material.

In gas-fired power stations, hot gases may drive the turbine directly. A gas-fired turbine may be switched on very quickly.

Biofuel is any fuel obtained from living or recently living organisms - a renewable source of energy can generate electricity.

Uranium and plutonium is used as the fuel in a nuclear power station ---> unranium is not burned; the enrgy comes from the process of nuclear fission.
> do no produce any greenhouse gases, however produces radioactive waste (needs to be stored for a long period of time) 

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4.2 Energy from wind and water

Energy from wind, waves and tides are renewable energy - can never be used up.

The movement of water is used to drive the turbine directly.

A wind turbine is an electricity generator on top of a tall tower - dilute, sound/visual pollution.

Waves generate electricity by turning a floating generator - hazardous to boats.

Hydorelectricity generators are turned by water running downhill - pumped storage system, starts up quickly, must be wet and hilly, flooding.

A tidal power station traps each high tide and uses it to turn generators - is reliable, affects ecology.

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4.3 Power from the Sun and the Earth

Solar cells transfer solar energy directly into electrical energy --> heats water flowing through the solar heating panel / transfer light to electric, dilute.
A solar power tower uses thousands of mirrors to reflect sunlight onto a water tank to heat the water and produce steam.

Geothermal energy come from inside the Earth --> radiactive processes heat rocks, in volcanic or other suitable areas, very deep holes are drilled, cold water is pumped down to the rocks, steam comes up and drives the turbines, near

In a few parts of the world,  hot water comes to the surface-heats buildings nearby.

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4.4 Energy and the environment

Burning fossil fuels produces greenhouse gases that cause global warming.

Nuclear fuels produce radioactive waste.

Using renewable resources can affect plant and animal life.

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4.5 The National Grid

The National Grid distributes electricity from power stations to our homes. Cables are carried long distances across the countryside supported by overhead pylons. In towns and close to homes the cables are buried underground.

The National Grid's voltage is 132 000V or more. Power stations produce electricity at a voltage of 25 000V.

Step-up transformers increased the voltage so transmission at high voltage reduces the energy wasted in the cables, making the system more efficient.

It would be dangerouse 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.

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4.6 Big energy issues

Base load demand is the demand for constant amount of electricity generated by power stations.

The demand for electricity varies furing the day and between summer and winter.

Gas-fired power stations and pumped-storage stations can meet variations in demand. When demand is low, energy is stored by pumping water to the top reservoir of pumped storage schemes.

Nuclear, coal and oil power stations can meet base-load demand.

Nuclear power stations, fossil-fuel power stations using carbon capture ans renewable energy are all likely to contribute to future energy supples.

Different types of pwer stations have different start-up times. Gas-fired power stations have the shortest start-up times and nuclear power stations have the longest.

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5.1 The nature of waves

We use waves to transfer energy and to transfer information.

Tranverse wave the oscillation (vibration) of the particles is perpendicular (at right angles) to the direction of energy transfer. All electromagnetic waves are transverse waves e.g. light waves and radio waves, can travel through a vacuum.

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. A sound is a longitudinal wave.

Mechanical waves, which need a medium (substance) tot ravel through, may be transverse or longitudinal waves e.g. waves on springs, and sound waves.

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5.2 Measuring Waves

Amplitude of a wave is the height og the wave crest or the depth of the wave tough from the position at rest. >> The greater the amplitude of a wave the more energy it carries.

Wavelength of a wave is the distance from one crest to the next crest, or from one trough to the next trough.

Frequency of a wave is the number of wave crests passing a point in one second. Unit for frequency is the hertz (Hz). Unit is equivalent to per second (s).

The speed of a wave is given by the equation; v = f x λ 

v is the wave speed in metres per second, m/s
f is the frequency in hertz, Hz
λ is the wavelength in metres, m

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5.3 Wave properties: reflection

The normal at a point on a surface is a line drawn perpendicular to the surface.

Angles are always measured between the light ray and the normal.

The law of reflection states that: the angle of incidence is equal to the angle of reflection.

The angle of incidence is the angle between the incident ray and the normal.

The angle of reflection is the angle between the reflected ray and the normal.

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

Virtual image cannot be formed on a screen, becuase the rays of light that produce the image only appear to pass through it.

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5.4 Wave properties: refraction

Waves change speed (causes a change in direction) when crossing a boundary between different subtances - wavelength also changes but frequency stays the same.

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 (e.g. air to glass).

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

Dispersion is when a ray of white light is shone onto a triangular glass prism and a spectrum is produced.

Violet ray is refracted the most.

Red light is refracted the least.

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5.5 Wave properties: diffraction

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

The narrower a gap is the greater the diffraction of the wave.

If radio waves do not diffract enough when they go over hills, radio and TV reception will be poor.

Bump up your grade
if you are drawing a diagram to show diffraction, make sure that the wavelength of the waves stays the same! 

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5.6 Sound

Sound is caused by mechanical vibrations in a substance, and travels as a wave ---> it can travel through liquids, solids and gases!....however, not through a vacumm...

The frequency range of the normal human ear is from about 20Hz to about 20kHz.

Sound waves are logitudinal waves.

Sound waves need a medium in which to travel.

Reflections of sound are called echoes.

Sound waves can be refracted (at the boundaries between layers of air at different temperatures) and also can be diffracted.

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5.7 Musical sounds

The pitch of a note increases if the frequency of the sound waves increases.

The loudness of a not depends on the amplitude of the sound waves.

Differences in waveform (are why there are different instruments that sounds different when played) can be shown on an oscilloscope.

Vibraions created in an instrument when it is played produces sound waves.

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6.1 The electromagnetic spectrum

The electromagnetic spectrum (in order of increasing wavelength);
- gamma rays
- X-rays
- ultraviolets
- visible
- infrared
- microwaves
- radio waves

All electromagnetic waves travel through a vacuum at the same speed but with different wavelengths and frequencies...!

Equation for the wave speed: v = f x λ

v is the wave speed = 300 000 000m/s
f is the frequency in hertz, Hz
λ is the wavelength in metres, m 

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6.2 Light, infrared, microwaves and radio waves

Visible light can be detected with our eyes where it enables us to see things in colours. 
----> it can be used for photography

Infrared is radiation emitted by all objects.

Microwaves are used in communications - able to produce wavelengths to pass through the atmosphere >> used to send signals to and from a network/satellitess

Radio waves transmit radio and TV programs and carry mobile signals.

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63 Communications

Radio waves of different frequencies are used for different purposes. Radio and microwave spectrum is divided into different bands ---> used for different communication purposes.

Microwave are used for satellite TV signals.

Research is needed to evaluate whether or not mobile phones are safe to use.

Optical fibres are very thin fibres that are used to transmit signals by light and infrared radiation
---> signals travel down the fibre by repeated total inter reflection.
>>> useful because they carry much more information and are more secure than radio wave and microwaves transmissions. 

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6.4 The expanding universe

Doppler effect is 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 source moves towards the observer, the wavelength decreases and the frequency increases.
>> when source moves away from the observer, the wavength increases and the frequency decreases.

Light from distant galaxies is red-shifted - wavelength increased and frequency decreased.

Blue-shift indicates that a galaxy is moving towards us.

Red-shift provides evidence that the universe is expanding. 

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6.5 The Big Bang

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 electromagnetic radiation creasted jest after the Big Bang.

At present CMBR can only be explained by the Big Bang theory.

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