Question

1. (a) What drives current? (b) What impedes current? (c) How does Ohm’s Law relate these quantities?
2. Why isn’t Ohm’s Law universally valid?
3. What is the resistance of an automobile headlight through which 3.50 A flows when 12.0 V is applied to it?
4. If a battery supplies energy to a circuit, what does the resistor do with that energy?
5. Calculate the effective resistance of a pocket calculator that has a 6.2 V battery and through which 0.20 mA flows.

Answer 1

(a)

Potential difference between terminals of an electrical device drives a current through the device.

(b)

Electrical resistance impedes the current. Resistance converts the kinetic energy of charge carriers to heat, slowing them down.

(c)

The potential difference V and electrical resistance R are related by Ohm's law as

where is the current flowing in the device.

A law is said to be universally valid if it hold for all systems under all conditions. But there are electrical components that do not follow Ohm's law, like semiconductors, diodes.

For the automobile headlight , the resistance is

If a battery supplies electrical energy to a circuit, the resistor converts that energy into heat energy.

For pocket calculator , the effective resistance of the calculator is