Edexcel A-Level Physics Conduction Model

Practise Edexcel A-Level Physics conduction model and resistivity through drift velocity, charge-carrier density, area and wire-current data.

Exam points

define drift velocity as the mean speed of free electrons or charge carriers
calculate drift velocity from I = nqvA using carrier density and cross-sectional area
explain drift-velocity changes from wire area, length, current and series-circuit constraints

[Maximum number: 3]

Drivers use car headlights to emit light in dark conditions.
The graph shows how current I varies with potential difference V for a car headlight.

Figure for Question 2.4.73 - Conduction model and resistivity question 1 — Edexcel A-Level Physics AS

The headlight will emit light when it dissipates at least 35 W of power.

The headlights are connected using copper wire. The current is $4.60\,\mathrm{A}$ . Calculate the drift velocity of electrons.

Number density $n=8.49 imes10^{28}\,\mathrm{m^{-3}}$

Resistivity $ho=1.72 imes10^{-8}\,\Omega\,\mathrm{m}$

Resistance per unit length $R/l=1.75 imes10^{-2}\,\Omega\,\mathrm{m^{-1}}$ .

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2.4.73 - Conduction model and resistivity question 1