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Showing 2 questions in Physics for Class 10. Tap a card to reveal the answer.
PhysicsElectricityeasyState Ohm's law and define electrical resistance.
Reveal answer ↓
What it is
For a conductor at steady temperature, voltage = current x resistance (V = IR).
Answer
Ohm's law states that, at constant temperature, the current I through a conductor is directly proportional to the potential difference V across it, so V = IR. Resistance R is the property of a conductor that opposes the flow of current; it is the ratio of potential difference to current, R = V/I, measured in ohm.
V = IR ; R = V/I
- •V is proportional to I at constant temperature
- •V = IR
- •R = V/I, unit ohm
- •Resistance opposes current flow
Why learn this
It's the single most-used rule in all electrical and electronics engineering.
💡 Memory trick
V = IR - the 'VIR' triangle: cover the one you want to find.
PhysicsElectricitymediumA current of 2 A flows through a 5 ohm resistor. Find the potential difference across it and the power dissipated.
Reveal answer ↓
What it is
Electric power is the rate of using electrical energy: P = VI (also I^2 R or V^2 / R).
Answer
Using Ohm's law, V = IR = 2 x 5 = 10 V. Power dissipated P = VI = 10 x 2 = 20 W (equivalently P = I^2 R = 4 x 5 = 20 W).
V = IR ; P = VI = I^2 R = V^2 / R
- •V = IR = 10 V
- •P = VI = 20 W
- •Check: P = I^2 R = 20 W
Why learn this
It's what your electricity bill charges for and why a heater draws far more than a phone charger.
💡 Memory trick
P = VI. If you know current and resistance, use P = I^2 R ('I-squared-R heating').