Electrical power
Heating up wires
As electronSubatomic particle, with a negative charge and a negligible mass relative to protons and neutrons. flow through wires, they collide with the ionElectrically charged particle, formed when an atom or molecule gains or loses electrons. in the wire which causes the ions to vibrateMove back and forth repeatedly (about a fixed point). more. This increased vibration of the ions increases the temperature of the wire. Energy has been transferred from the chemical energy storeThe different ways in which energy can be stored, including chemical, kinetic, gravitational potential, elastic potential and thermal stores. of the battery into the internal energy store of the wire.
The amount of energy transferred each second (powerThe energy transferred each second, measured in watts (W). Power = work done Ă· time taken.) between the energy stores can be calculated using the equation:
power = potential difference Ă— current
\(P = V \times I\)
This is when:
- power (P) is measured in watts (W)
- potential differenceThe potential difference (or voltage) of a supply is a measure of the energy given to the charge carriers in a circuit. Units = volts (V). This is the voltage between two points that makes an electric current flow between them. (V) is measured in volts (V)
- currentMoving electric charges, eg electrons moving through a metal wire. (I) is measured in amps (A)
One watt is equal to one joule per second (J/s).
Example
How much energy is transferred each second by a current of 2 amps (A) driven by a potential difference of 230 volts (V)?
\(P = V \times I\)
\(P = 230 \times 2\)
\(P = 460~W\)
Power can also be written as:
power = current2 Ă— resistance
\(P = I^2 \times R\)
This is when:
- power (P) is measured in watts (W)
- current (I) is measured in amps (A)
- resistanceThe opposition in an electrical component to the movement of electrical charge through it. Resistance is measured in ohms. (R) is measured in ohms (Ω)
Question
What power is dissipated by a current of 3 A through a 10 Ω resistorAn electrical component that restricts the flow of electrical charge. Fixed-value resistors do not change their resistance, but with variable resistors it is possible to vary the resistance.?
\(P = I^2 \times R\)
\(P = 3^2 \times 10\)
\(P = 9 \times 10\)
\(P = 90~W\)
Efficient transmission of power
Energy can be transferred by an electrical current; electrical appliances need to be given enough energy every second to work properly. Electrical power can be delivered as a low current with a high voltageThe potential difference across a cell, electrical supply or electrical component. It is measured in volts (V)., or a high current with a low voltage.
power = current2 Ă— resistance
The equation shows that a high current will have a much higher heating effect on the transmission wires than a low current. For this reason, transmitting energy at a high voltage with a low current will keep the wires cooler and waste less energy.