Types of current

• Current


  The rate of flow of charge
• In a metal wire, the charge is made of negatively charged electrons moving along the wire
• Electric charge


  Measured in coulombs (C)
• One coulomb is the charge that flows in one second when the current is one amp
• Charge cannot flow unless there is a complete circuit
• Direct current (dc)


  Electrons are attracted to the positive end of the battery and are repelled by the negative end
• Direct current (dc) is called so because the charge keeps moving in the same direction
• Batteries and cells supply direct current
• Alternating current (ac)


  Current constantly changes direction
• Mains electricity in the UK is usually 230V
• The frequency of mains electricity is 50 Hz
• Many electrical appliances need to be plugged in to complete the circuit
• Frequency


  The number of times the current changes direction in a second
• Oscilloscope


  A device used to visualize ac and dc
• Figure 2A shows ac, where the current is constantly changing direction
• Figure 2B shows dc, where the current is always in the same direction
• Direct current (dc)


  Stays the same
• Alternating current (ac)


  Constantly changes
• Batteries supply direct current
• Mains electricity is alternating current
• Devices using ac


  Toaster<|>TV<|>Hairdryer
• The UK mains supply is 230V ac with a frequency of 50Hz
• dc stands for direct current
• ac stands for alternating current