Electrical Energy & Power

Understanding Electrical Energy

Electrical energy is the energy that is caused by moving electric charges. It is a form of energy resulting from the flow of electric charge through a conductor.

The unit of electrical energy is the joule (J).

Electrical energy can be calculated using the formula:

$$E = P \times t$$

• Where E is the electrical energy in joules (J)
• P is the power in watts (W)
• t is the time in seconds (s)

Understanding Electrical Power

Electrical power is the rate at which electrical energy is transferred by an electric circuit. The unit of power is the watt (W).

Power can be calculated using the formula:

$$P = V \times I$$

• Where P is the power in watts (W)
• V is the voltage in volts (V)
• I is the current in amperes (A)

Relationship Between Energy, Power, and Time

The relationship between energy, power, and time can be summarized as:

$$E = P \times t$$

This means that the energy consumed by an electrical device is equal to the power it uses multiplied by the time it is in use.

Examples

Example 1: Calculating Electrical Energy

A light bulb has a power rating of 60 W and is used for 2 hours. Calculate the electrical energy consumed.

Solution:

• Convert time to seconds: $2 \text{ hours} = 2 \times 3600 = 7200 \text{ seconds}$
• Use the formula: $E = P \times t = 60 \times 7200 = 432000 \text{ J}$

Example 2: Calculating Power

An electric heater uses 240 V and draws a current of 10 A. Calculate the power of the heater.

Solution:

• Use the formula: $P = V \times I = 240 \times 10 = 2400 \text{ W}$