Power

In this lesson, we will learn:

• Meaning of power in electric circuits
• Three equations for power
• Solving problems involving power

Notes:

• Power (P) is the energy used by a circuit per unit time. It is a scalar measured in watts (W), where one watt is equal to one joule per second (1 W = 1 J/s).
  • For example: a 60 watt lightbulb uses 60 joules of energy every second, which it outputs in the form of light energy and heat energy.

Voltage Definition
V = $\large \frac{E_{p}} {q}$
V : Voltage, in volts (V)
E_p : Charge, in coulombs (C)
t : Time, in seconds (s)

Current Definition
I = $\large \frac{q} {t}$
I : Current, in amperes (A)
q : Charge, in coulombs (C)
t : Time, in seconds (s)

Ohm’s Law
V = IR
V : Voltage, in volts (V)
I : Current, in amperes (A)
R : Resistance, in ohms ($\Omega$)

Power
P = IV = I²R = $\large \frac{V^{2}} {R}$
P : Power, in watts (W)
V : Voltage, in volts (V)
I : Current, in amperes (A)
R : Resistance, in ohms ($\Omega$)