⇒ The rate at which energy is transferred by an appiance from one energy store to another is called the power

⇒ Power, P, potential difference, V, and current, I, are related by the equation: P = I x V

⇒ The potential difference provided by cells connected in series is the sum of the potential difference of each cell (depending on the direction in which they are connected)

⇒ For components connected in series:

• The total resistance is the sum of the resistance of each component



• There is the same current through each component



• The total potential difference of the supply is shared between the components

⇒ For components connected in parallel:

• The potential difference across each component is the same



• The total current through the whole circuit is the sum of the currents through the separate components

⇒ The resistance of a light-dependant resistor (LDR) decreases as light intensity increases

⇒ The resistance of a thermistor decreases as the temperature increases

⇒ One of the most fundamental properties that electronic engineers need to consider when designing electrical devices is the power transferred by the circuit in the device

• High power consumption requires specialist cooling systems and, if the device is battery powered, high battery capacity
• Minimising power consumption reduces costs and bulk

⇒ The electrical power transferred by a circuit is the sum of all the power transferred by the individual electrical components in the circuit

• The electrical power transferred by a component is related to the current flowing through it and the potential difference across it

⇒ The general definition of power is: power = rate of doing work or transferring energy

⇒ So, in an electrical context, electrical power can be defined as the rate of doing electrical work

⇒ The electrical power transferred by a component can be determined by using the current, the potential difference, and resistance of the component, and there are several equations that can be used to calculate this power

• These equations are produced by rearranging the basic equations for electrical current, potential difference and the definition of resistance:

⇒ Also see our notes on:

• Circuit Calculations
• Internal Resistance and Electromotive Force
• Resistor Networks
• Potential Dividers