# 2.3.1 Electrical Power

### Electrical Power

• Power is defined as

The rate of energy transfer or the amount of energy transferred per second

• The power of a device depends on:
• The voltage of the device
• The current of the device
• The power of an electrical component (or appliance) is given by the equation: • This equation can be rearranged with the help of a formula triangle: Power, current, voltage formula triangle

• The unit of power is the watt (W), which is the same as a joule per second (J/s)

#### Worked Example

Calculate the potential difference through a 48 W electric motor with a current of 4 A.

Step 1: List the known quantities

• Power, P = 48 W
• Current, I = 4 A

Step 2: Write down the relevant equation

P = IV

Step 3: Rearrange for potential difference, V Step 4: Substitute in the values #### Exam Tip

Remember: Power is just energy per second.

### Power & Resistance

• The voltage across an electric device depends upon the current and resistance of that device
• Using the equations P = IV with V = IR, power can be written in terms of resistance, R: #### Worked Example

Calculate the power through a 20 Ω resistor with a current of 6 A through it.

Step 1: List the known quantities

• Resistance, R = 20 Ω
• Current, I = 6 A

Step 2: Write down the relevant equation

P = I2R

Step 3: Substitute in the values

P = (6)2 × 20 = 720 W

#### Exam Tip

You can use the mnemonic “Twinkle Twinkle Little Star, Power equals I squared R” to remember whether to multiply or divide by resistance in the power equations

Which equation to use will depend on whether the value of current or voltage has been given in the question ### Author: Ashika

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
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