# Physics:

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## Heating houses:

• Energy in the form of heat, flows from a warmer to a coldfer body. When energy flows away from a warm object, the temperature of that object decreases.
• Temperature is a measure of 'hotness'. It allows one object to be compared to another.

Specific heat capacity:

All substances have a property called specific heat capacity which is:

• The energy needed to raise the temperature of 1kg by 1 degrees centigrade.
• Measured in joule per kilogram degree Celsius (J/kg degrees celsius).
• Different for different materials

When an object is heated and its temperature rises, energy it transferred.

The formula for specific heat capacity is:

energy transferred= mass x specific heat capacity x temperature change.

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## Heating houses:

Specific latent heat:

• Specific latent heat is the energy needed to melt or boil 1kg of material.
• The formula for specific latent heat is: energy transferred= mass x specific latent heat
• When a substance changes state, energy is needed to break the bonds that hold the molecules together. this explains why there's no change in temperature.
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## Keeping homes warm:

Energy:

• Different types of insulation cost different amounts and save different amounts of energy.
• Most energy is lost from the walls of an uninsulated house.
• Different energy sources each have their advantages and disadvantage. Cost can be compared by using a consistent unit- kWh.

Energy can be transferred by:

• Conduction- through solids.
• Convection- by movement of air, e.g. in a cavity wall.
• Radiation- across space without the need for a material, e.g. foil behind a radiatior.
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## How insulation works:

House insulation:

• Double glazing reduces energy loss by conduction. The gap between the two pieces of glass is filled with a gas or contains a vacuum.
• Solids are good conductors because the particles are close together. They can transfer energy very easily.
• Particles in a gas are far apart so its very difficult to transfer energy.
• There are no particles in a vacuum so its impossible to transfer energy by conduction.

Loft insulation reduces energy loss by conduction and convection:

• Warm air is in the home rises
• Energy is transferred through the ceiling by conduction.
• Air in the loft is warmed by the top of the ceiling.
• The warm air is trapped in the loft insulation.
• Both sides of the ceiling are at the same temperature, so no energy is transferred.

Without loft insulation:

• The warm air in the loft can move by convection and heat the roof tiles.
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• Infrared radiation doesn't penetrate food very easily but microwaves penetrate up to 1cm into food.
• Microwaves can penetrate glass or plastic but are reflected by shiny metal surfaces. Consequently because of this, the door of a microwave is made using a special reflective glass.
• Microwave radiation is used to communicate over long distances. The transmitter is used to communicate over long distances. The transmitter and receiver must be in line of sight. Aerials are normally situated on the top of high buildings.
• Satellites are used for microwave communication. The signal form Earth is received, amplified and then retransmitted back down to Earth. Satellites are in line of sight because there are no obstructions in space. The large aerials can handle thousands of phone calls and TV channels at once.
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## Electromagnetic spectrum:

Electromagnetic spectrum:

• Energy is transferred by waves.
• The amount of energy depends on the frequency or the wavelength of the wave.
• High frequency (short wavelength) waves transfer more energy.
• Gamma rays transfer most energy and radio waves the least.
• Normal ovens cook food by infrared radiation. Energy is absorbed by the surface of the food so the kinetic energy of the surface food particles increases. The rest of the food is heated by conduction.
• Microwave ovens cook food by microwave radiation. The water molecules in the outer layers of food vibrate more. Energy is transferred to the rest of the food by conduction and convection.
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## Microwaves:

Microwave properties:

• Microwaves have wavelengths between 1mm and 30cm.
• Mobile phones use longer wavelengths than microwave ovens. This means less energy is transferred by mobile phones.
• Microwaves don't show much diffraction around natural objects such as hills. Therefore the signal strength for mobile phones can change a lot over a short distance.
• Mobile phones can therefore interfere with sensitive equipment so they are banned on planes and in many hospitals.
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## Infrared signals:

Signals:

• Digital signals have two values: On and Off.
• Analogue signals can have any value and are continuously variable. The analogue signal changes both its amplitude and wavelength.
• Before an analogue signal is transmitted its added to a carrier wave. The frequency of the carrier wave is usually higher and the combined wave is transmitted.
• Interference from another wave can also be added and transmitted. If the wave is amplified the interference is amplified as well.
• Interference also occurs on digital signals, but it isn't apparent because the digital signals only have two values.
• Multiplexing allows are large number of digital signals to be transmitted at the same time.
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## Total internal reflection and critical angle:

• When light travels from one material to another, its refracted.
• If light is passing from a more dense material into a less dense material, the angle of refraction is larger the angle of incidence.
• When the angle of refraction is 90 degrees, the angle of incidence is called the critical angle.
• If the angle of incidence is bigger than the critical angle, the light is reflected. This is total internal reflection.
• Telephone conversations and computer data are transmitted long distance along optical fibres. Some fibres are coated to improve reflection.
• An endoscope allows doctors to see inside the body without the need for surgery.
• Light passes along one set of optical fibres to illuminate the inside of the body without the need for surgery.
• Light passes along one set of optical fibres to illuminate the inside of the body. The light is reflected and passes up another set of fibres to an eyepiece or camera.
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## Wireless signals:

• Radio waves are refracted in the upper atmosphere. The amount of refraction depends on the frequency of the wave. There's less refraction at higher frequencies.

Diffraction:

• When waves pass through a gap they diffract. The amount of diffraction depends on the width of the gap compared to the wavelength. Most diffraction occurs when the gap width is similar to the wavelength.
• Radio waves diffract around such things as mountains. The longer the wavelength, the more the diffraction.

Reflection:

• Radio waves are reflected from the ionosphere. Water reflects radio waves but land mass doesn't.
• Continued reflection by the ionosphere and the oceans allows radio waves to be received from an aerial that isn't in the line of sight.
• Microwaves pass through the ionosphere. They're received by orbiting satellites, amplified and retransmitted back to earth.
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## Communication problems:

Communication:

• Radio stations broadcast signals with a particular frequency. The same frequency can be used by more than one radio station because the distance between the radio stations means that only one will be received. However in unusual weather conditions, the radio waves can travel further and the broadcasts interfere.
• Refraction int he atmosphere needs to be taken into account when sending a signal to a communications satellite.
• The transmitting aerial needs to send a focused beam to the satellite because its aerial is very small. The transmitted beam is slightly divergent. Some energy is lost from the edge of the transmitting aerial because of diffraction.
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## Light:

Wave properties:

• The amplitude of a wave is the maximum displacement of a particle from its rest position.
• The trough of a wave is the displacement of a particle below its rest position.
• The crest of a wave is the displacement of a wave particle above its rest position.
• The wavelength of a wave is the distance between two adjacent points of similar displacement on the wave.
• The frequency of a wave is the number of complete waves passing a point in one second.
• The formula for calculating wave length is: wave speed= frequency x  wavelength.
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## Light:

Sending messages:

• When a signal is sent by light, electricity, microwaves or radio, its almost instantaneous.
• Each method of transmission has advantages and disadvantages.
• White light is made up of different colours of different frequencies out of phase.
• Laser light is at one frequency and is in phase.
• Laser light is used to read from the surface of a CD. The surface of the CD is pitted and the pits represent a digital musical signal. Laser light is shone onto the CD surface and the difference in reflection provides information for the digital signal.
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## Stable Earth:

Earthquake waves:

• The focus is where the earthquake happens below the surface. The epicenter is the point on the surface above the focus.
• L waves travel round the surface.
• P waves are longitudinal pressure waves: P waves can travel through the Earth at between 5km/s and 8km/s. P waves can pass through solids and liquids.
• S waves are transverse waves: S waves can travel through the Earth between 3km/s and 5.5km/s. S waves can only pass through solids.
• A seismograph shows the different types of earthquake wave.
• P waves travel through the Earth and are refracted by the core. The paths taken by P waves mean that scientists can work out the size of the Earth's core.
• S waves aren't detected on the opposite side of Earth to an earthquake because they won't travel through liquid. This tells scientists that the Earth's core contains liquid.
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## Weather effects:

• Natural events and human activity affect our weather.
• Dust from volcanoes reflect energy from the sun back into the atmosphere making it cooler on Earth.
• Dust from factories reflects radiation from towns back to Earth making it warmer on Earth
• Ultraviolet light on the skin causes the cells to make melanin, a pigment that products a tan. People with dark skin don't tan easily because ultraviolet radiation is filtered out.
• Use a sunscreen with a high SPF to reduce risks.
• The formula for the safe length of time to spend in the sun is: safe length of time to spend in the sun= published normal burn time x SPF.
• Ozone is found in the stratosphere. Ozone helps to filter out ultraviolet ratiation.
• CFC gases from aerosols and fridges destroy ozone and reduce the thickness of the ozone layer.
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