electricity

• The current is the flow of electrons around a circuit.
• A potential difference (PD) or voltage is the energy transferred from one charge to another when they are connected by a conductor.
• current is the rate of flow of charge
• in metal wires the charges are carried by negative electrons
• charge is measured in coulombs (C)
• equation for current:

  current = charge/time

  Q=I x T
• resistors can reduce the current
• a variable resitors resistance can be changed
• a fixed resistor is a resistor that has a fixed resistance value and cannot be changed
• as electrons flow around a circuit they gain energy
• when an electron goes through an appliance it loses its energy
• the voltage is the difference in energy between 2 points in the circiut
• current is measured in amps (A)
• current is the rate at which charge flows past a point in a circuit
• voltage = energy/charge

  V=E/Q
• fixed resistors are directly proportional
• current = voltage/resistance

  I=V/R
• ohms law states that current through a component depends on its resistance
• the greater the resistance the smaller the current for a given voltage across the component
• The steeper the gradient of a current–voltage graph, the lower the resistance of the wire.
• •Thermistors are a special type of resistor that is dependent on temperature


  •Uses: fire alarms, thermostats
• LDRs (light dependent resistors) are a special type of resistor that is dependent on light levels

  Uses: street-lighting
• Ammeters are always placed in series
• Voltmeters are always placed in parallel
• series circuits are when all of the components are added in a loop.
• If one component breaks, in a series circuit, the circuit does not work as it is not complete
• Voltage is shared between components, in a series circuit
• Current is the same in all parts of a series circuit as there is only one path for the electrons to follow
• •Total resistance is the sum of all the resistors in series
• parallel circuits is when all of the components are added in branches
• if one component breaks in a parallel circuit the circuit will still work as if it is a complete circuit.
• voltage is the same brightness in parallel circuits whereas in a series circuit the voltage is a different brightness
• current is shared on different branches in a series circuit
• •Resistance REDUCES when components are added in parallel