Physics GCSE

• Kinetic energy


  Energy of a moving object
• Gravitational potential energy


  Energy of an object due to its position above the ground
• Elastic potential energy


  Energy stored in a stretched or compressed object
• Transferring energy by heating

  1. Energy is transferred to the thermal energy store of the material

  2. Temperature of the material increases
• Specific heat capacity


  The amount of energy needed to raise the temperature of 1kg of a material by 1°C
• Insulation


  • Reduces the amount of heat lost
  • Examples: thick walls, loft insulation, cavity walls, double glazing
• Power


  The rate of transfer of energy - the amount of work done in a given time
• When an object falls

  It loses gravitational potential energy and gains kinetic energy
• When an object is stretched

  It gains elastic potential energy
• Energy can never be created or destroyed, just transferred from one form to another
• Some energy is transferred usefully and some energy gets transferred into the environment, which is mostly wasted energy
• Efficiency


  The ratio of useful output energy transfer to total input energy transfer
• Energy resources


  • Non-renewable (coal, oil, gas)
  • Renewable (e.g. solar, wind, hydroelectric)
• The UK is trying to increase the amount of renewable energy resources, but changing the fuels we use and building renewable power plants cost money
• Equations to calculate efficiency

  1. efficiency = useful output energy transfer / total input energy transfer

  2. efficiency = useful power output / total power input
• Some energy is always wasted. Nothing is 100% efficient
• Non-renewable energy resources


  Coal, oil, gas - they will all run out, they damage the environment, but provide most of the energy
• Renewable energy resources


  They will never run out, can be unreliable and do not provide as much energy
• Most of our electricity is generated by burning fossil fuels and nuclear. The UK is trying to increase the amount of renewable energy resources
• The governments are aware that non-renewable energy resources are running out; targets of renewable resources have been set
• Electric and hybrid cars are now on the market
• Changing the fuels we use and building renewable power plants cost money. Many people are against the building of the plants near them and do not want to pay the extra in their energy bills. Hybrid and electric cars are also quite expensive
• Energy resource advantages and disadvantages

  • solar - Renewable, no pollution, in sunny countries it is very reliable / Lots of energy needed to build, only works during the day, cannot increase power if needed
  • geothermal - Renewable and reliable as the rocks are always hot, power stations have a small impact on environment / May release some greenhouse gases and only found in specific places
  • wind - Renewable, no pollution, no lasting damage to the environment, minimal running cost / Not as reliable, do not work when there is no wind, cannot increase supply if needed
  • hydroelectric - Renewable, no pollution, can increase supply if needed / A big impact on the environment, animals and plants may lose their habitats
  • wave power - Renewable, no pollution / Disturbs the seabed and habitats of animals, unreliable
  • tidal barrages - Renewable, very reliable, no pollution / Changes the habitats of wildlife, fish can be killed in the turbines
  • biofuels - Renewable, reliable, carbon neutral / High costs, growing biofuels may cause a problem with regards to space, clearance of natural forests
  • non-renewable - Reliable, enough to meet current demand, can produce more energy when there is more demand / Running out, release CO₂, leading to global warming, and also release SO₂ which causes acid rain
• Useful power output = efficiency x total power input
• Useful energy output = efficiency x total energy input
• Required practical: Investigating Resistance in a Wire

  • Independent variable: length of the wire
  • Dependent variable: resistance
  • Control variables: type of metal, diameter of the wire
  • Conclusion: As the length of the wire increases, the resistance of the wire also increases
• Required practical: Investigating Series and Parallel Circuits with Resistors

  • Independent variable: circuit type (series, parallel)
  • Dependent variable: resistance
  • Control variables: number of resistors, type of power source
  • Conclusion: Adding resistors in series increases the total resistance of the circuit. In a parallel circuit, the more resistors you add, the smaller the resistance
• Required practical: Investigating I-V Relationships in Circuits

  • Independent variable: potential difference/volts (V)
  • Dependent variable: current (A)
  • Control variable: number of components (e.g. 1 filament bulb, 1 resistor), type of power source
• Equations


  • Charge: Q = It
  • Potential difference: V = IR
  • Energy transferred: E = Pt
  • Energy transferred: E = QV
  • Power: P = VI
  • Power: P = I2R
• Resistance


  voltage (V) = current (A) × resistance (Ω)
• Graphs of I-V Characteristics for Components in a Circuit

  • Ohmic conductor: the current is directly proportional to the potential difference - it is a straight line (at a constant temperature)
  • Filament lamp: as the current increases, so does the temperature. This makes it harder for the current to flow. The graph becomes less steep
  • Diode: current only flows in one direction. The resistance is very high in the other direction which means no current can flow
• Circuit Symbols


  • cell
  • closed switch
  • fuse
  • resistor
  • LDR
  • battery
  • voltmeter
  • LED
  • variable resistor
  • bulb
  • thermistor
  • open switch
  • diode
• Current


  The flow of electrical charge
• Potential difference (voltage)


  The push of electrical charge
• Resistance


  Slows down the flow of electricity
• 1kW = 1000W, 0.5kW = 500W, 50 000W = 50kW
• Static


  • A build-up of static is caused by friction. When materials are rubbed together, the electrons move from one to the other. One material becomes positively charged and the other is negatively charged. The positive charges do not move
  • Too much static can cause a spark. If the potential difference is large enough, the electrons can jump across the gap - this is the spark
  • Electric charges create an electric field. The closer you get to the object, the stronger the field. The electric field can be shown by drawing field lines, they go from positive to negative
  • If a charged object is placed near the field, it will experience a force. The force becomes stronger as the charged object gets closer
• LDR - Light Dependent Resistor


  An LDR is dependent on light intensity. In bright light the resistance falls and at night the resistance is higher
• Thermistor


  A thermistor is a temperature dependent resistor. If it is hot, then the resistance is less. If it becomes cold, then the resistance increases
• Electricity in the Home

  • Live wire - provides the potential difference from the mains
  • Neutral wire - completes the circuit
  • Earth wire - protection. Stops the appliance from becoming live. Carries a current if there is a fault