Physics Unit 1 Revision Notes PDF

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Physi Physics cs Unit 1 Revision Notes Radiation • • • •

Heat is transferred by radiation, conduction and convection. Radiation is transfer of heat by Infrared Radiation, whereas convection and conduction is transfer of energy by particles. Radiation occurs in solids, liquid and gas, however, convection only occurs in liquid and gas, and conduction only occurs in solids. There is a factor which effects the transfer of heat. The bigger the temperature change, the faster the transfer of heat. (Think of this like osmosis, and the concentration gradient)

Infrared Radiation • • • • • •

All objects emit Infrared Radiation. It is emitted from the surface of an object. The hotter an object, the more infrared radiation it emits in a time period. There are factors effecting how much an object emits and absorbs infrared radiation. For example, a dark and matt surface absorbs and emits more infrared radiation that a light and shiny surface. However, light and shiny surfaces reflect most of the radiation. You need to know this as the exam paper may give you an example of a real life situation, in which you will need to apply this.

Kinetic Theory • •

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There are three states of matter, solids, liquids and gases. They all have the same particles and etc, however there are little details which differ them. A solid has strong forces of attraction within each particle, therefore the particles are held closely together, in a fixed and regular arrangement. The particles also don’t have much energy; therefore, they only vibrate in their position. A liquid has weaker forces of attraction within each particle. This means that the particles are close, however not very close together. This means that the particles can move past each other and also form irregular arrangements. They have more energy than the particles in a solid. A gas has no force of attraction within each particle, so they are not close to one and another. The particles have more energy than the ones in liquids and solids, so they are free to move in random direction at very high speeds.

Conduction • •

Conduction of heat is where vibrating particles pass on their extra kinetic energy to their neighbouring particles. (The exam definition.) This process occurs in solids and the extra kinetic energy causes a rise in temperature throughout the solid.

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Conduction is usually faster in denser solids as the particles are closer together. Solids with less space within each particle conduction heat slower (such as a bubble foam) Metals are generally good conductors due to their property. They have free electrons which can move around the metal. This gives them an advantage as the electrons can pass their energy to other ions and electrons by collision.

Convection • • •

Convection is when more energetic particles from a hotter region to a cooler region and carry their energy with them. (This is the exam definition) Convection occurs naturally in the Earth’s mantle, and is responsible for the plate movements. However, convection is also taken to our advantage by using them as radiators in a home.

Condensation • •

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This is when gas turns to liquid. When a gas cools, the particles slow down, because they have less energy. This means that the electrostatic force can pull them together, to form clumps which eventually form liquid. A common example is when water vapour gets in contact with a cold surface, such as a mirror next to a shower. (this was actually an example in a past paper.) The rate of condensation is faster if the temperature of the gas is lower. This means that more particles will join together due to the electrostatic force and form liquid. The rate of condensation is faster if the surface the particles touch is smaller, as this reduces the average energy per particle. The rate of condensation is faster if the density if higher. This is because the electrostatic force is bigger, so particles will require much higher energy to overcome that. If the airflow is slower, then the particles have less energy and can get closer to each other, to form liquid.

Evaporation • • • • •

Evaporation is when particles escape from a liquid, and turn into gas. This is when a liquid is heated, the particles gain energy. This allows them to overcome the electrostatic force and escape the liquid into the air as gas. However, as the energetic particles escape, the overall energy of the liquid decreases. This is because the particles left over do not have enough energy to escape. This commonly happens in our body, which produces sweat.

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The rate of evaporation is faster is the temperature of the liquid is bigger. If the temperature if bigger, then the average energy per particle is higher, which means that more particles have enough energy to escape. The rate of evaporation is faster if the density if lower. This is because the electrostatic force is weaker, so less energy per particle is needed to overcome that. If the surface area of the liquid is bigger, then there are more particles closer to the surface to escape, so the rate of evaporation is faster. If the airflow if greater, then the concentration gradient is steeper, which means that the rate of evaporation is greater.

U-Values • •

A U-Value of an object shows how fast heat can transfer through a material. If the U-Value is smaller, then it means that the material is a good insulator.

Energy Transfer • • •

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The principle of energy states that energy can be stored, transferred and dissipated, however, energy cannot be destroyed nor made. Energy can only be useful, when it is converted from one form to another. An example of this is a battery. A battery stores chemical energy, which is transferred to electrical and heat energy. The heat energy is the useless energy, which gets dissipated. Nothing every produces full useful energy. This is because nothing is 100% efficient. A common exam question is when a scenario is given, and you can describe in ways in which the useless energy can be used. For example, heat from a power station can be used to heat homes. The energy transfer of useful and useless can be shown using a Sankey diagram.

Energy Sources • •

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There are two types of energy sources, renewable and non-renewable. Some examples of non-renewable energy sources include: coal, oil and natural gas. They will run out one day, and also they do the most damage to our environment. Ironically, they are also the ones mostly used. Some examples of renewable energy sources include: wind, waves and geothermal. They will never run out and do the least amount of damage to our environment. Surprisingly, they are not used a lot, however it’s because sources such as wind are not very reliable and they don’t provide much energy. A typical power station works by burning fuels such as coal or gas. This heats up water, and the steam from the water spins a turbine. The turbine simple spins the generator, which produces electricity. They are then distributed into the grid. The energy transfers take place as so in a power station: Chemical energy  Heat energy  Kinetic energy  Electrical energy. The energy source is simply used to spin a turbine.

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A nuclear power station is not the same as a regular coal power station, however it does still use the movement of turbines. The only difference is that it used fuel rods, such as plutonium and uranium to heat up the water. Wind power works by simply having turbines on an open landscape. The winds simply spin the turbines, which spin generators. A solar station works in a different way. The sunlight from the sun is used to give electrical current to electrical components. This is only effective for tools such as calculators and etc. Hydroelectric power is used in remote areas such as the Andes mountains. For this a steep condition and a dam is required. The water from the dam, or reservoir is simple released and the flowing movement of the water spins turbines, which spins a generator. The method used in hydroelectric power can also be used in the coast line, where little turbines are placed and they spin as the waves travel. Geothermal energy is when the heat from things such as volcanoes and etc are used to spin a turbine. Biofuels is the use of dead plants which is burned to spin a turbine. The problem is that power stations running on coal and gas have environmental issues as they produce harmful gases such as sulphur and etc into the atmosphere. Biofuels have similar impact; however, they release the CO2 which the plant was absorbing as they burn. This increases the impact of global warming.

The National Grid • •

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Electricity from the power stations is distributed by the National Grid, which is a mixture of pylons and cables. The problem with this is, we need to transmit a high amount of power. However, for this, we either need to have a high current or voltage. Using a high current means that the energy loss is increased by radiation along the cables. Therefore, a high voltage is used, and the voltage is increased and reduced at transformers. This is so that it is safe to use in a home. At the power station, there will be a step-up transformer, which increases the voltage. Near the homes, there will be a step-down transformer, which reduces the voltage, so that it’s safe to use in homes. There are two ways to transmit electricity. You can either use overhead cables or underground cables. There are advantages and disadvantages of using both methods. Using an overhead cable means that the set up cost is cheaper, whereas using an underground cable means that the set up cost is more expensive. Using an overhead cable means that the maintenance is higher, due to a lot of factors acting on it. Whereas the maintenance of an underground cable is smaller due to less factors acting on it.

Waves • • • • • • •

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There are two types of waves; transverse and longitudinal waves. Most waves are transverse, including the electromagnetic spectrum. In a transverse wave, the vibrations are perpendicular to the energy transfer. Examples of longitudinal waves include sound waves and shock waves. In a longitudinal wave, the vibrations are parallel to the energy transfer. All waves can be reflected, refracted and diffracted. Reflection is when waves “bounce” of a surface. The angle at which the wave travels to the normal is the incident ray. The angle at which the wave is bounced off to the normal line is the reflected ray. Due to the laws of reflection angle of incidence = angle of reflection. Diffraction is when waves spread out, as they travel through a gap. If the gap is wider, then the waves diffract a little. If the gap is smaller, then the waves diffract a lot. Refraction is when the direction of a wave changes as it travels from a dense to less dense material (or less dense to dense). This is because as they do, their speed changes.

Electromagnetic Spectrum • • •

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The electromagnetic spectrum consists of radio waves, microwaves, infrared, visible light, ultraviolet, x-rays and gamma rays. All the electromagnetic waves are different in wavelength, and due to that, they are used for different purposes. Radio waves are used for communication. This is because they have long wave length, which makes them useful for diffraction around in mountain areas. Also, they can be reflected off the ionosphere. Microwaves are used for satellite communication and mobile phones. (Ironically, they are also used in microwaves, yes, the actual box thing.) Infrared waves are used by TV remotes and optical fibre. Visible light is used for photography. Sound travels are waves. In fact, they travel as longitudinal waves. They can reflect and refract. The reflect property can be heard in a small box room. Reflected sound waves are echoes. Sound cannot travel in space because of no particles. The higher the frequency of sound waves, the higher the pitch. The loudness of the sound waves depends on the amplitude.

The Universe (This section is a bit muddled up, feel free to fix it) • • •

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The universe is expanding, and the red-shift proves it. Another way of referring to the red-shift is The Doppler Effect. The Doppler effect is when an object moves closer to you, the frequency is higher and the wavelength is shorter. When the object moves away, the frequency is lower, and the wavelength is higher. This applies to both longitudinal waves and transverse waves and can also explain how the Red-Shift works. The Red-Shift is due to the fact that different elements absorb different frequency.

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Each of the elements produce a specific pattern on the visible spectrum. This is used in the Red-Shift. When we look at light from the distant galaxies, we see the same patterns on the visible spectrum, however they are slightly shifted towards the red end. The bigger the red-shift, the further and faster the galaxy is moving away from us.

The Origin of the Universe. • • • •

According to evidence, the Origin of the Universe began with a big bang. This is supported by the Big Bang Theory. The theory is that the universe started with a big bang and is expanding ever since. Another theory is the “Steady State”, the theory that the universe has always been the same, and will always be the same. However, the discovery of the Cosmic Microwave Background Radiation was a strong evidence for the Big Bang Theory....