Resistance

Question 1

Resistance

Answer 1

As electrons are accelerated by potential difference across a circuit, they collide with metal ions in the wire. Each time this happens, kinetic energy is transferred to thermal energy in the wire, causing it to increase in temperature.

Therefore, materials with free electrons (metals) require a smaller potential difference to produce the same current. They have low resistance and are called conductors. Some materials don’t have free electrons, and so they offer significant resistance to the flow of charge. They are called insulators.

Question 2

Ohm’s Law

Answer 2

At a given temperature, the current (I) flowing through a wire is directly proportional to the voltage drop across it. Resistance is defined as the ratio of potential difference to current: R = V/I

Question 3

Ohmic vs Non-Ohmic Resistors

Answer 3

A device is said to be ohmic if it follows Ohm’s Law. Ohmic devices include wire and heating elements. Ohmic resistors have a fixed resistance (constant gradient).

Non-ohmic resistors have varying resistance with temperature - will not follow Ohm’s law.