What is Watt's law for electrical power in a resistor in terms of current and resistance?

What is Watt's law for electrical power in a resistor in terms of current and resistance?

• A. P = I × I × R
• B. P = V × I
• C. P = V × V / R
• D. P = R × I

Answer: (A)

Power dissipated in a resistor depends on how much current flows and how much resistance there is. This is expressed as P = I^2 R. You get it by starting with P = VI and using Ohm’s law V = IR. Substituting V with IR gives P = I·(IR) = I^2 R. This shows the power increases with the square of the current and linearly with resistance. Other common forms involve voltage, like P = VI or P = V^2 / R, which aren’t written purely in terms of current and resistance, and P = R × I would not have the correct units for power.

Power dissipated in a resistor depends on how much current flows and how much resistance there is. This is expressed as P = I^2 R. You get it by starting with P = VI and using Ohm’s law V = IR. Substituting V with IR gives P = I·(IR) = I^2 R. This shows the power increases with the square of the current and linearly with resistance. Other common forms involve voltage, like P = VI or P = V^2 / R, which aren’t written purely in terms of current and resistance, and P = R × I would not have the correct units for power.