Ohmic and non-ohmic conductors and I-V characteristics

An I-V characteristic.

What does it mean when an I-V characteristic is a straight line through the origin?

I∝V, so it is an ohmic conductor.

What is an ohmic conductor?

A conductor that follows Ohm’s law.

What is ohm’s law?

A conductor follows Ohm’s law when current is directly proportional to p.d. for a range of p.d. values, and resistance is constant.

I-V characteristic of a filament lamp:

I-V characteristic of a diode:

Resistor/ ohmic conductor I-V characteristic:

Explain the I-V characteristic of a filament bulb or hot conducting wire.

As p.d. increases, some of the energy is converted into the kinetic energy of the atoms and free electrons in the conductor, i.e the conductor’s temperature increases. This means more collisions and therefore a higher resistance.

For the same increase in p.d., the current increases by a smaller amount for larger p.d. values.

There is a narrow section where the graph is linear, therefore resistance is constant.

Explain the I-V characteristic of diodes and LEDs.

Below 0V, there sis no resistance, so current is large.

Above 0V, resistance decreases as p.d. increases, therefore current increases.

What can diodes and LEDs be defined as in terms of conduction?

Semi-conductors- they allow current to flow one way.