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Physics (Electricity (Current, potential difference and resistance, Energy…

- - - - As more and more resistors are added in parallel to a circuit, the equivalent resistance of the circuit decreases and the total current of the circuit increases. Adding more resistors in parallel is equivalent to providing more branches through which charge can flow.
    - - When two or more components are connected in parallel, the potential difference across them is the same. This means that if a voltage across a lamp is 12 V, the voltage across another lamp connected in parallel is also 12 V.
    - - More resistance means less current is flowing through the circuit. Equivalent resistance is a different way of indicating 'total' resistance, which we calculate differently for series and parallel circuits.
    - - The current is the same everywhere in a series circuit. It does not matter where you put the ammeter, it will give you the same reading.
  - - - colour- wire
        blue -neutral
        brown- live
        green and yellow stripes -earth
      - The features of a plug are:
        The case is made from tough plastic or rubber, because these materials are good electrical insulators.
        The three pins are made from brass, which is a good conductor of electricity.
        There is a fuse between the live terminal and the live pin.
        The fuse breaks the circuit if too much current flows.
        The cable is secured in the plug by a cable grip. This should grip the cable itself, and not the individual wires inside it.
    - - In direct current (DC), the electric charge (current) only flows in one direction. Electric charge in alternating current (AC), on the other hand, changes direction periodically. The voltage in AC circuits also periodically reverses because the current changes direction.
  - - - • the length of a wire at constant temperature
      - combinations of resistors in series and parallel
    - - An ohmic conductor is a conductor that obeys Ohm's law. That's all. Ohm's law are expressed as following: V=RI (directly proportional)
    - - Filament lamp
        
        The filament lamp is a common type of light bulb. It contains a thin coil of wire called the filament. This heats up when an electric current passes through it, and produces light as a result.
        A graph with current on the y axis and voltage on the x axis. A slightly curved line goes through the graph at 45 degrees
        The resistance of a lamp increases as the temperature of its filament increases. The current flowing through a filament lamp is not directly proportional to the voltage across it. This is the graph of current against potential difference for a filament lamp.
      - Diode
        
        Diodes are electronic components which can be used to regulate the potential difference in circuits and to make logic gates.
        Circuit symbol for diode
        Diode
        The diode has a very high resistance in one direction. This means that current can only flow in the other direction. This is the graph of current against potential difference for a diode:
    - - Use a multi meter that is connected in parallel to the component.
  - - - Electricity is supplied to consumers through the National Grid at a very high voltage to reduce energy losses during transmission. Transformers are used to increase or decrease the voltage of the supply. Electricity is charged in units. One unit is equivalent to one kilowatt of electricity used for one hour.
    - - Power is a measure of how quickly energy is transferred. The unit of power is the watt (W). You can work out power using this equation:
        Power(watt, W) is equal to energy (J) divided by time (S).
- - - - Heat is thermal energy. It can be transferred from one place to another by conduction, convection and radiation. Conduction and convection involve particles, but radiation involves electromagnetic waves.
    - - Heat loss through walls can be reduced using cavity wall insulation. This involves blowing insulating material into the gap between the brick and the inside wall, which reduces the heat loss by conduction. The material also prevents air circulating inside the cavity, therefore reducing heat loss by convection.
  - - - Solar panels are useless in cloudy environments. Wind turbines are useless in still environments. Need to choose where to put them sensibly
    - - Our society uses more and more energy every year, but the carbon dioxide produced by most power stations is believed to be causing serious damage to the climate.
      - The nuclear industry is regularly inspected to ensure that standards of safety are maintained.
    - - COAL - Burnt to provide heat or electricity.
      - NATURAL GAS - Often used in houses for heating and cooking.
      - NUCLEAR - Electricity is generated from the energy that is released when the atoms of these minerals are split (by nuclear fission) in nuclear reactors.
      - BIOMASS -
        
        It can also be an organic material which is burned to provide energy, eg heat, or electricity.
        
        After treatment with chemicals it can be used as a fuel in diesel engines.
      - WOOD - Obtained from felling trees, burned to generate heat and light.
    - - Disposal of nuclear waste raises ethical problems:
        Some people say that we must have nuclear power, or we will not be able to combat global warming and still produce enough energy.
        Others say that it is unethical to produce waste that will still be dangerous in many thousands of years’ time.
      - Many developing countries insist that they need to burn fossil fuels in their power stations, even if it produces global warming. They need this to allow them to catch up with the standard of living that we enjoy.
    - - Most non-renewable energy sources are fossil fuels: coal, petroleum, and natural gas.
      - Our renewable energy resources will never run out. Their supply is not limited. There are no fuel costs either. And they typically generate far less pollution than fossil fuels.
        Renewable energy resources include:
        wind energy
        water energy, such as wave machines, tidal barrages and hydroelectric power
        geothermal energy
        solar energy
        biomass energy, for example energy released from wood
  - - - The specific heat capacity of a substance is the amount of energy needed to change the temperature of 1 kg of the substance by 1°C.
    - - A device that stores energy is sometimes called an accumulator. Energy comes in multiple forms including radiation, chemical, gravitational potential, electrical potential, electricity, elevated temperature, latent heat and kinetic.
- - - - Specific heat is the amount of heat required to raise the temperature of a substance a certain amount. Latent heat is the amount of heat released during a change of state, i.e. the boiling of water or the melting of ice.
  - - - pressure1 × volume1 = pressure2 × volume2
    - - pressure1 × volume1 = pressure2 × volume2
    - - Particles in both liquids and gases (collectively called fluids) move randomly. This is called Brownian motion. They do this because they are bombarded by the other moving particles in the fluid. Larger particles can be moved by light, fast-moving molecules.
  - - - SOLID- Very difficult to squash, can't be poured, can't change shape. LIQUID - difficult to squash, can be poured, can change shape. GAS - easy to squash, can be poured, can change shape
    - - The particles in a substance stay the same when it changes state - only their closeness, arrangement or motion change. This means that:
        the chemical nature of the substance itself stays the same
        the mass of the substance stays the same
        For example, 10 g of water boils to form 10 g of steam, or freezes to form 10 g of ice. This is called conservation of mass.
- - - - Atoms are made of extremely tiny particles called protons, neutrons, and electrons. Protons and neutrons are in the center of the atom, making up the nucleus. Electrons surround the nucleus. Protons have a positive charge. Electrons have a negative charge.
      - Isotopes are atoms that have the same number of protons and electrons, but a different number of neutrons.
    - - https://vceasy.files.wordpress.com/2014/02/1-1-2a1.png
  - - - Alpha Decay: The atomic mass number decreases by 4
        The atomic number decreases by 2
      - Beta Decay:The atomic mass number stays the same
        The atomic number increases by 1
    - - Not only does it decay by giving off energy and matter, but it also decays at a rate that is characteristic to itself. The rate at which a radioactive isotope decays is measured in half-life. The term half-life is defined as the time it takes for one-half of the atoms of a radioactive material to disintegrate.
    - - Alpha radiation Alpha radiation is the least penetrating. It can be stopped - or absorbed - by just a sheet of paper.
        Beta radiation Beta radiation can penetrate air and paper. It can be stopped by a thin sheet of aluminium.
        Gamma radiation Gamma radiation is the most penetrating. Even small levels can penetrate air, paper or thin metal. Higher levels can only be stopped by many centimetres of lead or many metres of concrete.
    - - Damages living tissue
      - precautions: Time (limiting or minimising the expose time reduces the dose from the radiation source. Distance the dose of radiation decreases dramatically as you increase the distance from the source. Shielding barriers of lead, concrete or water provide protection from penetrating gamma rays and x-rays.
    - - The Geiger-Muller tube detects radiation. Each time it absorbs radiation, it transmits an electrical pulse to a counting machine. This makes a clicking sound or displays the count rate. The greater the frequency of clicks, or the higher the count rate, the more radiation the Geiger-Muller tube is absorbing.