Electricity

You will be able to

• Use I = Anvq to calculate the drift velocity of charge carriers in a conductor.
• Explain why the drift velocity is greater in the thinner part of a wire carrying a steady current.
• Compare the drift velocity in a metal and a semiconductor carrying the same current, in terms of number density.

You will be able to

• Use R = ρL / A to calculate the resistance of a wire or the resistivity of its material.
• Determine the resistivity of a metal from the gradient of a graph of R against L, with its uncertainty from a worst acceptable line.
• Explain why a non-zero intercept (contact resistance) does not affect a value found from the gradient.

You will be able to

• Sketch and explain the I–V characteristics of a metallic conductor at constant temperature, a filament lamp and a semiconductor diode.
• Calculate resistance as V / I at a point on a characteristic, not from the gradient of the curve.
• Explain how the resistance of an NTC thermistor falls with temperature and that of an LDR falls with light intensity.