Electricity - OCR GatewayElectrical power - Higher
The electricity used in homes, shops, hospitals and factories has to be transported large distances from power stations without energy being lost to the surroundings.
In an electrical circuit, energy is transferred each second. This is electrical powerThe energy transferred each second, measured in watts (W). Power = work done 梅 time taken.. The power output of a transformer can be calculated using the equation:
power = potential difference 脳 current
This is when:
power is measured in watts (W)
potential difference (pd) is measured in volts (V)
current is measured in amperes 鈥 also referred to as amps (A)
Assuming that a transformerAn electrical device that increases, or decreases, the potential difference (voltage) of an alternating current. is 100 per cent efficient, the following equation can be used to calculate the power output from the transformer:
pd across primary coil 脳 current in primary coil =
pd across secondary coil 脳 current in secondary coil
Example
A step-down transformer converts 11,500 V into 230 V. The power output is used to run a 2,000 W kettle. Calculate the current flowing in the primary coil (the input current).
Note, the power in each coil will be the same, since transformers are 100 per cent efficient.
Power = 2,000 W
Rearrange the formula to find current:
Current in primary coil = power 梅 potential difference in primary coil
The equation above only works if energy cannot be dissipatedTransferred to the surroundings. through heat, or other ways. In reality, as energy is transferred, the core and wires in the transformer will heat up due to induced currents. The amount of heating depends on the resistanceThe opposition in an electrical component to the movement of electrical charge through it. Resistance is measured in ohms. of the wires and how big the current is.