Moving and storing heat
When as substance is heated , it's particles gain energy. In a liquid the particles move around faster and in a solid the particles vibrate quicker. This is measured in a absolute scale meaning it can't go below zero because there is a limit to how slow particles can move.(Joule -J)
The hotter something is the higher the temperature.(degrees Celsius or degrees Fahrenheit) Energy seems to flow from hotter objects to cooler ones. Like warm radiators to the cold air that surrounds it.
It takes more heat energy to increase the temperature of some materials meaning it releases lots pf energy when it cools down. They can ''store'' a lot of energy. The measure of how much energy a substance can store is called specific heat capacity. The specific heat capacity in water is high. Once water is heated it stores a lot of energy, which makes it good for central heating systems - it's a liquid so can be pumped around a building.
Energy = mass x specific heat capacity x tempurature change. Use Triangle
Melting and Boiling
When you heat a liquid, the heat energy makes the particles move faster. Eventually when the particles have enough energy to overcome their attraction to each other, big bubbles of gas start to appear in the liquid (boiling). It's similar in a solid. Heat energy makes the particles vibrate quicker until eventually the forces between them are overcome and the particles start to move around (melting) When a substance is melting or boiling you are still putting in energy, but the energy is used to break intermolecular bonds rather than raising the temperature.
When a substance is condensing or freezing bonds are forming between particles, which release energy. This means the temperature doesn't go down until all the substances have turned into a liquid (condensing) or a solid (freezing).
Heat - How hot something is.
Tempurature - measurement
Specific Latent Heat
The specific latent heat of melting is the amount of energy needed to melt 1kg of material without changing it's temperature (already be at melting temperature already) The specific latent heat of boiling is the energy needed to boil 1kg of material without changing in temperature (already be at boiling temperature already) It's different for different materials, and different for boiling and melting.
Energy = mass x specific latent heat
Example- The specific latent heat of water (melting) is 334 000 j/kg. How much energy is needed to melt an ice cube of mass 7 g at 0 c?
Answer- Energy = 0.007 x 334 000 J = 2338J
Conduction and convection in the home
Conduction occurs mainly in solids. Lots of heat is lost through open and closed windows. In a solid the particles are held tightly together. So when one particle vibrates, it bumps into another particle nearby and quickly passes on the vibration. Particles that vibrate quicker pass on extra kinetic energy to neighbouring particles. These particles then vibrate faster. The process continues throughout the solid passing on kinetic energy (or heat). This causes a rise of temperature on the other side. Conduction of heat is the process where vibrating particles pass on extra kinetic energy to neighbouring particles.
Convection occurs in liquids and gases. When you heat up a liquid or gas the particles move faster, and the fluid (liquid or gas) expands, becoming less dense. The warmer less dense fluid rises above it's colder, denser surroundings, like a hot air balloon. As the warm fluid rises, cooler fluid takes its place. As this continues, you actually end up with a circulation of fluid (convection currents). Convection occurs when the more energetic particles move from the hotter region to the cooler region- and take their heat energy with them. Radiators rely on convection to warm up a room continuously. Convection can't happen in solids because the particles can't move.
Radiation is how we get heat from the sun. Heat is radiated from infarred rays and travel in straight lines at the speed of light. Radiation is different to conduction and convection because it can occur in a vaccum, like space. This is the only way heat reaches us from the sun. It can only occur through transparent substances, like air, glass and water. The amount of radiation emmited or absorbed by an object depends to a large extent on it's surface colour and texture.
All objects are contiunessly emmiting and absorbing heat radiation. The hotter the object gets the more radiation it emits. Cooler objects will absorb the heat radiation emmited by hotter ones around them. Matt black objects are verry good absorbers and emmiters of radiation. You should really paint radiator black (absorbs it) and fridge white (reflect it). Grills and toasters heat food by radiation. The heat radiated by a grill is absorbed by the surface particles of the food, increasing the kinetic energy. The heat energy is then conducted or convected to more central parts.
Over - exposure to heat radiation damages body cells and causes burning.
How to save energy - Insulate house, double glazing, hot water tank jacket, thick curtains, Draught proofing and cavity wall. Other ways we can reduce energy loss - turn off lights, turn TV of standby and close windows.
What is Pay back time - the amount of time it takes for someone to start saving money.
Pay back time = Cost of insulation ÷ annual saving
Cavity wall works by.. The best insulation is air but it does have to be still air. That means not moving by convection or draft. As the air moves it removes heat from the surface over which it passes. The heat that it is removing from a cavity wall is coming through the inner wall to the cavity and it then transfers to the outer wall which because, especially in winter, it is cold takes the heat and passes it to the outside.
Putting foam or rockwool or other insulating products into the cavity stops the air movement and therefore stops the transfer of heat to the outside.
Useful machines are only useful because they convert energy from one form to another (like a car). The total energy output is the exactly the same as the energy input, but only some of the output energy is useful. So for every joule of chemical energy you put in your car only a fraction of it is converted into useful kinetic energy. This is because some of the input energy is always lost or wasted (often heat). The less energy wasted, the more efficient the device is.
The more efficient machines waste less energy.
Efficiency = Useful Energy Output ÷ Total energy output x 100 to get percentage.
Waves have certain features. The amplitude is the displacement from the rest position to the crest. The wavelength is the length of a full cycle of the wave e.g crest to crest. Frequency is the number of complete waves passing a certain point per second (measured in Hetz Hz)
All waves can be reflected, Refracted and diffracted. Reflected just like light is in the mirror so you can see yourself. Waves are refracted which means they change direction which is why shapes change shape when looked through water. Waves can also be diffracted. This means the wave bends around obstacles, causing the waves to spread out more.
Radio waves and microwaves are good at sending infomation long distances . This is beacuse they don't get absorbed by the earth's atmosphere as much as the waves in the middle of the EM spectrum (like heat) or those at the high freqeuency end of the spectrum (gamma rays).
When a wave comes up to something with a lower density, it changes speed (refraction). If the wave hits the boundary face on, it slows down but carries on in the same direction.Now has a shorter wavelength but the same frequency. But if the wave meets a different medium at an angle, part of the wave hits the denser layer first and slows down while another part carries on at the first, faster speed for a while. So the wave changes direction- been refracted.
Radio waves- UV radiation from the sun creates layers of ionised atoms (atoms that have either gained or lost electrons). Radio waves travel faster through ionised parts of the atmosphere this causes refraction. Medium wave radio uses wavelengths of about 300 m. These are refracted most in ionosphere (back to earth) meaning they can be received miles away from the transmitter. The amount a wave is refracted in the ionosphere depends on its frequency and angle of elevation. Refraction sometimes can disrupt a signal by bending it away from the receiver dish.
Waves can interfere with each other. When two or more waves similar frequency come into contact, they can create one combined signal with a new amplitude (interference)You get it when two radio stations transmit on similar frequencies.
Wireless communication and ovens
Diffraction is when waves spread out and bend round corners. Diffraction works by all gthe waves spreading out at the edges when tehy pass through a gap or past an object. The amount of diffraction depends on the size of the gap relative to the wavelength of the wave. The narrower the gap, or the longer the wavelength the more the wave spreads. Diffraction cause problems though. It can occur on the edges of dishes used to transmit signals. This results in signal loss (weaker).
Microwaves don't diffract much meaning the dishes have to be positioned in line of sight (hill tops and close together) If there is something between you and the transmitter you would probably have poor signal.
Microwave ovens uas a different wavelength from mobiles.Microwaves for communication need to pass through the earth's watery atmosphere but the microwaves in mircrowave ovens have a different wavelength. These are absorbed by water molecules in the food. They penetrate a few centimetres into the food before being absorbed and increasing their kinetic energy. The energy is then conducted or convected to other parts. Some microwaves can damage your health but no no proof.
Communicating with light
Optical fibres can carry data over long distances as pulses of light or infrared radiation. They work by bouncing rays off a very narrow core which is protected by outer layers.The light enters one end of the fibre and is reflected again and again until it emerges at the other end. Very quick way to communicate. They only work because of total internal reflection, all the light is reflected when the light ray hits the side of the inner core. Total internal reflection can only happen when the light ray travels through a dense substance like glass, water or perspex towards a less dense substance like air. It all depends on the angle of incidence of the ray. If this angle is big enough (bigger than the critical angle), the ray doesn't come out at all, but reflects back into the glass. If the angle of incidence is .. Less than the critical angle: most of the light is refracted into the outer layer, but some of it is internally reflected. ..Or Equal to the critical angle the ray would go along the surface (with quite a bit of internal reflection as well. .. Greater than the critical angle no light comes out. It's all internally reflected (total internal reflection). Optical fibres and electrical wires send can send lots of information, light, radio and electrical signals are great because the signals send fast. Cables can be difficult to be repaired that's why wireless is so good.
An analogue wave can take any value within a certain range (rounded). A digital signal can only take two values. these values seem to be called on/off.
Both digital and analogue signals weaken when they travel, they need to be ampified along their route. Interferance also causes random disturbances (noise) which can lead to a poor signal. When you amplify a analogue signal, the low amplitude noise is amplified too (everytime amplified the signal looses quality). With a digital signal yhe low-amplitude noise is ignored so has no affect. Digital signal can send more than one at the smae time using just one cable.
Cd players are read by lasers. This is because on a CD they have patterns of shallow pits cut into it.Thge areas between the pits are called lands. The laser gets reflected from the shiny surface of the CD when it spins around. Reflected from a land and a pit slightly differently and this can be picked up by a light sensor which then can be changed into an electrical signal. It's the change in the reflected beam which represents on and no change is Off. The amplifier and a loudspeaker then convert this to sound of the right pitch (frequency) and loudness.
Humans and the enviroment
The more time you spend int the sun, the more chance you also have of getting skin cancer. This is because the sun rays include ultraviolet which damages the DNA in your cells. Dark skin absorbs more UV rays so have some protection, this prevents the rays getting to the more vulnerable tissue deeper down. Everyone should wear protection at suitable SPF. If you wore SPF of 15 you could spend 15 times the amount you would in the sun.
The ozone layer protects us from UV radiation (made up of three oxygen atoms). It absorbs them. Ozone layer has got thinner because of CFCs meaning more rays are coming in.
Natural events and human activities affect weather patterns. In cities building absorb and store heat during the day and late it out at night. But dust pollution works as a blanket and traps heat radiation in. so cities tend to be warmer than the countryside. Dust from volcano reflects radiation from sun. Less radiation get through to earth meaning it's cooler.
Wave speed = frequency x wavelength
Example- Eva is building a sandcastle. She estimates that 1 wave passes her sandcastle every 2 seconds, and that the crests of the waves are 90cm apart. Caculate the speed, in metres per second, of the waves passing Eva's sandcastle.
Answer- speed =0.5 x 0.90 =0.45 m/s
You always have to convert your units first. 1 kHz (kilohertz) = 1000 Hz 1MHz (megahertz) = 1000 000 Hz
The speed of light = 3 x 10 8 m/s = 300 000 000 m/s.
When there is a earthquake shock waves get sent out across the earth (seismic waves) Seismologists measure the time it takes for the shock waves to reach each seismograph and where they don't reach at all. There are two different seismic waves that travel through the earth, P-waves and S-waves. P-waves are longitudinal. The vibrations are along the direction that the waves travel. Vibrations this way <--> wave travelling this way -->. they refract when density changes. They travel through solids and liquids and faster than S-waves. Can go through core.S-waves are transverse. The vibrations are at right angles to the direction the wave travels. vibrations up and down. Wave travelling this way -->. S-waves only travel through solids and are slower than P-waves. Can't pass through liquid outer core.
Halfway through the earth,P-waves change direction abruptly meaning there is a sudden change of properties (mantle to core). S-waves don't go through outer core meaning it's liquid. P-waves go slightly faster through core suggesting it is solid. Mantle is solid seeing as S-waves pass through it (only melts to form magma in hot spots). Change of speed causes waves to change direction (refraction). usually change speed gradually resulting in a curved path. When speed changes suddenly the wave changes speed abruptly and the path has a kink.