GCSE Physics Electricity

Created by: RyEC
Created on: 19-02-18 16:01

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Physics - Electricity
- Static Electricity
  - This is electricity that does not move - it builds up
  - Like charges repel
  - Unlike charges attract
  - Uses include: -Paint/crop spraying; Photocopier; smoke/dust precipitators
  - Static Charge results from the loss or gain of electrons by friction
    - Loss = positive
    - Gain = negative
  - Dangers: aeroplane refuelling; lightning; shocks
  - Earthing safely discharges surplus charge from an insulator
  - Conductors allow charge to flow; insulators do not
- Charge flow
  - Measured in coulombs (C)
  - 1A of current = 1C of charge passing a point per second
  - Charge = current x time
    - Q = It
- Current and circuits
  - Conventional current flows from positive to negative
    - Electrons flow from negative to positive
  - The potential difference (voltage) is define by the energy transferred per unit charge
    - Voltage = energy/charge
      - V = W/Q
      - Measured in volts (V)
        1V = 1J/C
  - The current is the same in all parts of a series circuit
    - The current will divide among the branches of a parallel circuit
      - The total voltage in a series circuit is shared/split across its components
        The voltages across each branch in a parallel circuit are equal
  - Ohm's law is that the current flowing through a metallic conductor (or resistor), held at constant temperature, is directly proportional to the potential difference across
    - Voltage = current x resistance
      - V = IR
    - If heat increases so too does resistance
      - The length of the wire is directly proportional to resistance if temperature, material and CSA are constant
        If CSA increases then resistance will decrease
        Different materials have different resistances (depends on # of delocalised electrons)
        The length of the wire is directly proportional to resistance if temperature, material and CSA are constant
        If CSA increases then resistance will decrease
        Different materials have different resistances (depends on # of delocalised electrons)
  - In series: Total resistance = R1+R2+R3+...
    - In parallel: 1/Rt = 1/R1+1/R2+...
  - Power
    - Electrical power = current x voltage
      - P=IV
    - Energy transferred = power x time
      - P=Et
- Household Electricity
  - Energy(kWh) = Power(kW) x time(h)
  - Neutral wire - bLue to the Left
  - Earth wire - middle, yellow+green
  - Live wire - bRown to the Right
  - A fuse contains a metal wire that will melt if current exceeds a stated value
    - Choose the fuse that is closest to but above the standard operating current
    - Double insulation can be used as an alternative to earthing
  - Types of current
    - a.c. - alternating current (from mains), changes direction regularly
      - Used in National Grid for transformers
        Vs/Vp=Ns/Np
        Transformer equation:
        
        Step-up transformer: increases voltage; decreases current; more turns on secondary coil than primary
        
        Step-down transformer: decreases voltage; increases current; more turns on primary coil than secondary
        
        Power in = power out and P=IV so if voltage increases then current decreases
    - d.c. - direct current (from battery), always flows in one direction
  - Electromagnetic induction

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GCSE Physics Electricity

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