# Physics P 1 Energy for the home

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## P1a Understanding heat and temperature

Heat is a form of energy

Temperature is a measure of the kinetic energy of particles in a substance.

Thermogram - a graphic or visual record produced by thermography.

Objects transfer energy to their surroundings quicker if the temperature difference between the object and surroundings is greater.

Specific heat capacity= measures the thermal energy stored

The specific heat capacity of a substance is the amount of energy in joules needed to change the temperature of 1 kg of the substance by 1°C. Different substances have different specific heat capacities.

Amount of energy needed to change temp depends on - Mass -Material- size of temp change

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## P1a Specific latent heat

Specific latent heat measures the amount of energy needed to change the state of a substance.

Energy (j) = mass (kg) x specific latent heat (j/kg)

Change of state - Changing from one physical state to another e.g. solid to liquid

Fusion - Melting (not to be confused with nuclear fusion.

Vaporization - the conversion of a solid or a liquid into a gas.

Intermolecular bond -Bond between particles of a substance.

Intermolecular forces are forces of attraction or repulsion, which act between neighboring particles (atoms, molecules or ions).

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## P1 b Conduction and convection a

Houses lose energy by conduction and convection , reduced by good insulation. Cavity walls reduce energy loss by adding cavity wall insulation which traps air in pockets, preventing convection.

Energy is transferred from one type to another by applainces at home. Calculating energy efficiency helps reduce wasted energy.

Solids transfer energy when their closely packed particles vibrate about fixed positions.Kinetic energy is passed between particles. This is called conduction.

Liquids and gases have particles free to move and transfer energy by convection. Gas is heated and expands, becomes less dense and rises. Change of density causes fluid flow as rising warm gas is replaced by falling colder gas , which has higher density.

Convection current is set up that transfer heat through the gas. Same for liquids.

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## P1 b Conduction and convection b

Conduction- One way of transferring energy by vibrations being passed from one particle to another.

Thermal Conductor - Property of a material to conduct heat.

Thermal insulator - Material that does not conduct heat well.

Free electrons - Electrons that move freely and independently through a substance.

Fluid - a substance that has no fixed shape and yields easily to external pressure; a gas or a liquid

Convection - How thermal energy is transferred by the movement of particles in fluids.

Convection current - The movement of particles by convection when heat energy is transferred.

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## P1 b Radiation and surfaces

All objects emit and absorb infrared radiation as electromagnetic waves.

Because no particles involved radiation can work through vacuum of space - heat of the sun. Objects can absorb radiation from the sun, temperature in sunlight increases.

Dark matt objects good infrared radiation emitters and light shiny objects are not.

Emit - To give out

Medium - Any substance that a wave passes through e.g. air water metal

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## P1 b Insulating your home and energy efficiency

Heat Source - A heat source is anything that can heat up the surrounding air.

Payback time - How long it takes to make money back when paying for a resource.

Cost effective - Describes when the cost of making a change is low in relation to the resultant savings in energy bills.

Efficiency = how much energy is usefully transferred.

Sankey diagram - Sankey diagrams summarise all the energy transfers taking place in a process. The thicker the line or arrow, the greater the amount of energy involved.

Energy can be transferred usefully, stored or dissipated; it cannot be created or destroyed. This is called conservation of energy.

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## P 1 c Waves

Waves travel at various speeds and have characteristic peaks and troughs.

Oscillations = vibrations travelling through space.

Transverse waves oscillations are at right angles to direction of travel and energy transfer e.g. light and other types of electromagnetic radiation.

Longitudinal waves oscillations travel same direction as direction of travel and energy transfer

Amplitude - The maximum displacement of a wave or oscillation.

Wavelength -The distance between two wave peaks.

Frequency - The number of oscillations per second for a vibration.

Wave equation - The speed of a wave equals its frequency multiplied by its wavelength.

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## P 1 c Electromagnetic waves and wave experiments

Electromagnetic waves travel at the speed of light.

They do not need a medium can travel through vacuum- space.

Infrared waves and microwaves are used for cooking food.

Electromagnetic waves are used to communicate: infrared (remote control): radio waves (radio and TV): microwaves (mobile phones)

Reflection - Occurs when waves bounce off objects

Law of reflection - Angle of incidence = angle of reflection

Refraction - Change of speed and direction of a wave when it passes from one medium to another.

Diffraction - Spreading out of waves when they pass through a gap or around an obstacle.

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## P 1 d Total internal Reflection, Fibre Optics and

Fibre optic cables transfer information using light. Light travels through the denser of two materials and it's angle is greater than the critical angle of the two mediums. Total Internal Reflection occurs.

Total Internal Refelection - When a wave travelling inside a denser medium reflects off the boundary with another medium, and so stays inside the original material.

Critical Angle - Smallest angle of incidence for which total internal reflection takes place.

Optical Fibre - A fine glass tube designed so light can travel through it by total internal reflection.

Endoscope - A medical instrument which uses optical fibres to produce an image of the inside of a patient.

Phase - Waves that are in step with each other. Their crests line up with other crests.

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## P1 e Waves cooking and communicating

Infrared waves and microwaves are used for cooking food.

Electromagnetic waves are used to communicate: infrared (remote control) : radio waves ( radio and TV) : microwaves (mobile phones)

Microwave - Wave that fits between radio waves and infared in the electromagnetic spectrum.

Line of sight - Straight line path followed by light from an object to an observer.

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## P 1 f Analogue and Digital

Two ways to transmit data signals

Analogue signals have varied values and are susceptible to interference and noise.

Digital signals are either 1 or 0 (on or off ) series of pulses, so the signal can be interpreted correctly. Advanatges interference, noise can be easily removedexcellent picture or sound quality.

Multiplexing - A technique used to transmit several digital signals at once.

Noise - Random signal with no meaning.

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## P 1 g Wireless communication

Wireless Communication- communicating via electromagnetic waves.

Aerial - a rod, wire, or other structure by which signals are transmitted or received as part of a radio or television transmission or receiving system.

Ionosphere - the layer of the earth's atmosphere, which contains a high concentration of ions and free electrons and is able to reflect radio waves.

Advantages = no phone line needed, portable, convenient

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## P 1 h Seismic waves and our Atmosphere

Seismic waves are of two main types: longitudinal P waves and transverse S waves.

Seismometer - an instrument that measures and records details of earthquakes, such as force and duration. Often as a displacement time graph

P waves - Seismic esve whose oscillations are in the same directions of travel. Sometimes called pressure, primary or push waves.

S waves -  Seismic wave whose oscilllations are at right angles to the direction of travel. Sometimes called secondary, shear or shake waves.

Ultraviolet radiation - is a type of electromagnetic wave. The wavelengths are shorter than those of ordinary, visible violet light but longer than those of x-rays. and have a lot of energy.

Sun protection factors 0 Measure of how much longer a sun cream allows you to sunbathe safely.

Ozone layer in the atmosphere blocks UV radiation.

UV Light causes tanning and can cause cancer.

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