Electricity

Electric current §

• charges move
• Conventional current flow:
  • Current move from positive to negative
• Actual current flow:
  • Electrons move from negative to positive
• Unit for current is Ampere (A)
  • Ammeter used to measure current
    • Must be connected in series to circuit
    • Should have 0 resistance to current flow

Ammeter setup:

Potential Difference and Electromotive Force §

• Potential Difference (p.d.) -> work done to drive a unit charge through the component
• Electromotive Force (e.m.f) -> work done by the source to drive a unit charge around a complete circuit
• Unit for p.d. and e.m.f is Volt (V)
• e.m.f. is the amount of electrical energy produced by a source while p.d. is the electrical energy converted to other forms of energy when a unit positive charge moves from one point to another in a component
• Voltmeter used to measure p.d.
  • Must be connected in parallel
  • Should have infinite resistance

Voltmeter setup:

Electrical Symbols §

Resistance §

• Ratio of Potential Difference across it to the current flowing through it
• Hinders flow of charge
• Formula:
• S.I. unit is ohm ()
• Used to control the size of current flowing in a circuit

Fixed resistor	Variable resistor
fixed value of resistance	variable resistance
e.g. carbon film resistors, carbon composition resistors, tin oxide resistors, wire-wound resistors	e.g. rheostat

Diagram of how rheostat works:

Effective Resistance §

Resistors connected in series §

• Resistance of multiple resistors can be combined into one singular large resistor
• Effective resistance of resistors:

• Current in series circuit is constant
• Voltage of source:

Resistors in parallel §

• p.d. of resistors are the same
• Effective resistance of resistors:
• Current:

Electrical Power §

Formula for power:

• S.I. unit is watt (W)
  • Watt = J/s

Amount of electrical energy used: usually use kilowatt hour