Spring term physics

Spring term physics

1. Voltage and Power

   • Electrons experience a force
     • Accelerate down the wire/resistor
       • Towards +
         • Electron defficient terminal
     • I = Q/T =Amps
     • Do work and give it electrical potential energy
   • Energy per charge (V)= Energy(J)/Charge(C)
     • Potential difference = applied across a component
     • Electromotive force = applied across a cell/battery
   • Kirchoff
     • Law 1: I1= I2 + I3
       • current into junction = current out
       • Conservation of charge
     • All voltages in closed loop sum to zero
   • Energy = Voltage*Current*time
   • Power = Current*voltage
   • Series or parallel
     • Series: Voltage is shared out between every component. Good for low power lighting
       • Rtotal = R1 + R2
     • parallel:If one component breaks, the rest can continue to be used so practical. Good for high power as voltage is equal over the whole circuit
       • 1/Rtotal = 1/R1 +1/R2
   • Resistance
     • V=IR
       • Ohms law
     • Thermistor
       • R^ when temp^
     • LDR
       • R^ when light^

2. Mains electricity

   • AC Vs DC
     • DC: Current flows in only one direction. Cant use transformers and expensive
     • Changes direction constantly at 50Hz (UK mains). Cheap, efficient at travelling long distances. More likely to directly affect the hearts natural rhythm
   • Safety hazards
     • Frayed cables exposes live wires
     • Longer cables have more risk of over heating due to more resistance
     • Damaged plugs may have safety features broken
     • Water near sockets conducts electricity so electrocution/fire risk
   • Safety features
     • Insulation
       • live wire with material that doesnt conduct
     • Double insulation
       • Live wire is insulated within the casing
     • Earthing
       • If the current touches the case, it will be directed through the earth wire to the ground
     • Fuses
       • Melts the connection when current is too high
     • RCDs
       • Electromagnet pulls apart the circuit when current is too high
         • can be rest
         • Can be switched on/off
   • resistor gives off heat which can be used in appliances such as electric heaters

3. Energy transfer

   • Energy efficiency = useful energy/energy input
   • Conduction/Convection/radiation
     • Conduction
       • Flow of heat without matter
         • Good conductors - metals
           • Radiators can heat a room quickly
     • Convection
       • Flow of heat with matter
         • Hot liquid rises, Cool liquid falls
       • Insulation
         • prevents convection
     • Radiation
       • Flow of heat due to electromagnetic radiation
         • Body heats up by absorbing radiation from sun