Practice question

**Potential difference drop** across resistor when current flows because charges lose potential energy qV = I² R t as heat, field E = V/l drives drift, maintaining current. At very high E, velocity saturation or heating changes τ, causing non-ohmic behaviour. Maximum power transfer occurs when the external resistance equals the internal resistance ( R = r ), as P = I² R = (ε / (R + r))² R . Internal resistance limits current, influencing the power distribution. Applying I = n e A v_d, R = ρ l/A, R_t = R₀[1+αΔT], Kirchhoff's ΣI=0, ΣV=0, R_eq series/parallel, V = ε - I r and