# GCSE Physics Electricity

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