# Physics P1

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All objects emmit + absorb infrared radiation from their surface

An object hotter than surroundings emmits more radiation to cool down

An object cooler than surroundings absorbs more radiation than emmits to heat up

Dark matt surfaces - good absorbers + good emmiters of radiation

Light, shiny surfaces - poor absorbers (good reflectors) + poor emmiters

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## Kinetic Theory

Used to explain the three states of matter - solid, liquid + gas

When substance heated, particles given kinetic energy so vibrate + move faster

Solids - strong forces of attraction, fixed regular arrangement + little energy so particles only vibrate around fixed position

Liquids - weaker forces of attraction, irregular arrangement + more energy so move in random directions at low speed

Gases - almost no forces of attraction + most energy so move freely in random directions at high speed

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## Kinetic Theory

Used to explain the three states of matter - solid, liquid + gas

When substance heated, particles given kinetic energy so vibrate + move faster

Solids - strong forces of attraction, fixed regular arrangement + little energy so particles only vibrate around fixed position

Liquids - weaker forces of attraction, irregular arrangement + more energy so move in random directions at low speed

Gases - almost no forces of attraction + most energy so move freely in random directions at high speed

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## Conduction

Conduction of heat energy is the process where vibrating particles pass on their extra kinetic energy to neigbouring particles

Faster in denser solids (e.g. metals) because particles are closer together so collide more and pass energy between them - conductors

Less dense materials have larger spaces between them so not as fast - insulators

Occurs mainly + more easily in solids

Metals are good conductors because electrons are free to move inside the metal

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## Convection

Only occurs in liquids and gases

Occurs when the more energetic particles move from the hotter region to the cooler regions and take their heat energy with them

Immersion Heater:

1) heat energy transfered from heater coils to nearby water by conduction

2) particles near coils get more energy so start moving faster

3) therefore water becomes less dense and rises above lees dense, cooler water

4) the cooler water sinks to bottom and then is heated up - causing a cycle

Radiator example same but replace water with air

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## Condensation

When a gas turns to a liquid

1) when a gas cools the particles slow down and lose kinetic energy - come closer together

2) if particles get close enough together condensation takes place

e.g. water vapour in air condenses on cool surfaces such as drink glases

Rate faster if:

temperature of gas is lower

temperature of surface is lower

density is higher

airflow is lower

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## Evaporation

When a liquid turns to gas

1) when particles escape from liquid

2) particles can escape when the particles are moving in the right direction and at a fast pace to overcome attractive forces of other particles

3) the fastest particles are most likely to escape so the energy of remaining particles decreases

4) this drop means the temperature of remaining liquid drops (cooling effect) e.g. sweat

Rate faster if:

temperature is higher

density is lower

surface area larger

airflow greater

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## Rate of Heat Transfer

Large surface area - increased rate of heat transfer e.g. motorbike engines have fins

Heat sinks = devices designed to move heat away from objects

Smaller volume - cools quicker

Good conducters - cools quicker

Depends on material in contact with e.g. if in contact with conductor rate quicker than insulator

Bigger temperature difference between object and surroundings - faster rate of energy transfer

Adaptations - animals in warm conditions have bigger ears to increase surface area and therefore heat loss

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## Heating and Insulating Buildings

U-values - measure how effective a material is as an insulator by measuring how fast heat can pass through an object e.g. lower u-value better material is as an insulator

Payback time - time taken for money saved to equal money spent

Insulating examples - cavity wall insulation, loft floor insulation + thick curtains

Solar panels - contain water heated by sun and used to heat buildings

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## Energy Types

Eletrical energy - whenever a current flows

Light energy - from sun, lightbulbs etc

Sound energy - from loudspeakers or anything noisey

Kinetic energy - movement energy

Nuclear energy - from nuclear reactions

Thermal energy - heat energy

Gravitational potential energy - possesed by anything that can fall

Elastic potential energy - possesed by springs, elastic etc

Chemical energy - possesed by fuels, batteries etc

(Bold = stored energy)

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## Energy Transfer

Energy can be: transferred usefully from one form to another, stored or dissipated but can never be created or destroyed

Some energy is always wasted in energy transfer (usually as heat)

Less energy wasted = more efficient

Efficiency = useful out ÷ total power/energy in

Sometimes waste energy can be used e.g. heat from car engine used in car heating system

Energy = power x time

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## Non-Renewable Energy Sources

Will all run out

Damage enviroment

Provides most of our energy

e.g.

• coal
• oil
• natural gas
• nuclear fuels

(bold - fossil fuels)

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## Renewable Energy sources

Never run out

Less damage to enviroment

Unreliable and doesn't provide as much energy

e.g.

• wind
• wave
• tides
• hydroelectric
• solar
• geothermal
• food
• biofuels
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## Power Stations

Most electricity generated from non-renewable sources of energy in power stations

1) fuel burned to convert stored chemical energy into heat energy

2) heat energy then used to heat water or air to produce steam

3) the steam turns a turbine, converting heat energy into kinetic energy

4) the turbine is connected to a generator, kinetic energy into electrical energy

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## Wind Power

Windmills in exposed places e.g. hills + coasts

Each turbine has generator so electricity created directly from wind

+ no pollution

+ no fuel or running cost

+ no permanent damage to landscape

- spoils view

- noisy

- no power when winds stops

- high startup costs

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## Hydroelectric Power

Requires flooding a valley by building a dam usually in a remote valley

Rainwater caught in dam and sent through turbines

+ quick to set up

+ reliable

+ no fuel or running costs

+ useful to generate electricity on a small scale in remote areas as uneconomical to connect to national grid

- loss of habitat

- flooding permanently damages landscape and causes rotting vegetables which increases CO2 levels in atmosphere

-High initial costs

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## Wave Power

Lots of small turbines around coast powered by up and down motion of waves

+ no pollution

+ no fuel or running costs

+ useful on small islands

- spoils view

- hazard to boats

- unreliable as depends on wind

- high startup costs

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## Tidal Barrages

Big dams built across river estuaries with turbines in them

When the tides comes in the estuary fills up and drives turbines with water let through

The source of energy is gravity from the sun and moon

+ no pollution

+ reliable

+ good for storing energy for times of peak demand

+ no fuel costs and minimal running costs

- prevents access by boats

- spoils view

- affects habitat of animals

- high startup costs

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## Solar Cells

Generates energy directly for sunlight

+ can be used for things such as calculators and watches which don't use much energy

+ can be used in remote places e.g. outback

+ reliable in certain places

+ virtually no running costs

+ no pollution

- often impractical or too expensive to connect to national grid

- unreliable in countries without consistent sun

- high initial costs

- not enough energy generated for large scale use

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## Geothermal Energy

Volcanic areas where hot rocks lie near to the surface

The source is the slow decay of radioactive elements

Steam + hot water rise to surface + are used to drive a generator

Can sometimes be used to directly heat buildings

+ no real enviromental problems

+ cheap to maintain

- aren't many suitable locations

- high startup costs

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## Energy Issues

All fossil fuels release CO2 into atmosphere when burned which adds to the greenhouse effect and therefore global warming

Burning coal and oil releases sulfur dioxide which causes acid rain

Coal mining causes mess of landscape

Oil spillages cause enviromental problems

Nuclear power is clean but nuclear waste is dangerous and hard to expose of and nuclear power plants expensive and risk disaster e.g. Chernobyl in 1986

Things to consider:

• Set up costs
• Reliability issues
• Enviromental issues
• Running costs
• Location issues

Carbon capture - collects CO2 from power stations before it is released into atmoshere

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## National Grid

Takes elecrical energy from power stations to homes

High voltage needed to transmit everywhere and low current to prevent energy loss as heat

Transformers used to step voltage up at one end for efficient transmition and down to safe levels for use

Overhead or underground cables used with different benefits

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## Waves

Waves transfer energy from one place to another

Either transverse or longitudinal

Transverse:

• most waves including electromagnetic and light
• vibrations perpendicular (90°) to direction of energy transfer
• looks like a slinky wiggled up and down

Longitudinal:

• vibrations along straight line (parallel to direction of energy tansfer)
• sound waves and shock waves
• looks like slinky pushed at one end

Amplitude - distance from rest position to crest (upwards)

Wavelength - length (across) of full cycle of wave

Frequency - number of complete waves passing a certain point per second (measured in hertz)

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## Electromagnetic Wave Spectrum

Em waves with different wavelengths have different purposes + properties

Higher frequency = shorter wavelengths

All electromagnetic waves travel at the same speed through a vacuum (space)

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## Uses of Electromagnetic Waves

• used for communication
• long-wave can be tranmitted very far + recieved halfway around the world as diffracted (bent) so recieved even if not in line of sight
• short-waves and medium-waves reflect of ionsphere so don't have to be in line of sight

Microwaves

• satellite communication + mobile phones
• used as can pass through earths atmosphere to satellites from transmitters
• microwaves in phones are potentially dangerous as some wavelengths are absorbed by water molecules and heated up which could be dangerous if these cells are in your brain

Infrared waves

• used in remote controls as different patterns of waves are sent to apply different commands to an appliance
• optical fibres have pulses of visible light or inrared radiation reflected up and down in core of fibre

Visible light - lenses control how much light enters a camera and shutter speed determines how long film or sensor is exposed to light

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## Refraction

Changing the speed of a wave and changing its direction

When a wave crosses a boundary betwen two subjects (e.g. glass to air) it changes its direction

If the wave hits a medium face on it carries on in the same direction (angle of incidence 0)

If it hits medium at any angle the wave changes direction

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## Diffraction

Waves spread out at edges when they pass through a gap or obstacle

Amount of diffraction depends on size of gap relative to wavelength so the narrower the gap/longer the wavelength, the more it spreads out

A narrow gap = one with same size gap as wavelength

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## Reflection

When a light traveling in the same direction reflects off an even surface it's reflected at the same angle

Law of reflection - angle of Incidence = angle of reflection

Normal - perpendicular to reflecting surface

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## Plane Mirror Reflection

The image is:

• same size as object
• as far away from the mirror as object
• virtual
• laterally inverted (left and right swapped around)

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## Sound Waves

Longitudinal waves

We hear sounds from vibrations in a medium

Can't travel in space as in a vaccum (no particles)

Denser - sound travels faster e.g. fastest in solids

Sound waves reflect better on hard, flat surfaces (echoes)

Refract when enter different surfaces

Higher frequency = higher pitch - determined by vibrations each second

Higher amplitude = louder sound

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## Red Shift

The universe is expanding and red shidt supports this

Red shift:

• different elements absorb different frequencies of light
• when looking at light from different galaxies the same pattern is shown but more towards the red end of the spectrum at slightly lower frequencies
• distant galaxies have greater red shift than nearer ones, therefore distant galaxies are moving away faster than nearer ones (expanding)

Doppler effect

• frequency of car moving towards you will seem higher and the frequency of a car moving away will seem lower
• happens with both longitudinal and transverse waves
• 1) sound waves from stationary car are spaced out equally
• 2) wavelengths are more spaced out behind moving car
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## Origin of Universe

Big bang theory:

• all matter and energy in universe compressed into small space and then exploded
• expansion still occuring
• doesn't explain everything e.g. what was before and what caused explosion

• main alternative theory
• suggests everything same everywhere and expansion is creation of matter

• eletromagnetic waves filling the universe
• explained by big bang theory
• after big bang the universe was very hot and emmited high frequency frequency radiation
• this radiation has cooled to drop in frequency to microwave radiation
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