Equations involving power
Power (P) is the energy transferred over time or rate of transfer of energy. It can be calculated by multiplying the voltage across a component by the current flowing through it:
P = V I
Where V is the voltage and I is the current.
As power is the energy transferred per unit time, you can multiply power by time to find the energy transferred (W).
W = Pt
W = V It
Where V is the voltage, I is the current and W is the energy transferred.
Below is an example in which you need to use the above formulas:
A lamp has a power of 60 W, and is connected to a power source of 240 V. Find the energy transferred by the lamp in 2 minutes and the current in the lamp.
To find the energy transferred you can use the formula , making sure time is W = Pt converted into seconds.
W = 60 × 120 = 7200 J
To find the current, you can use the (rearranged) formula I = P / V
I = 60 / 240 = 0.25 A
