Maximum power is transferred from a source to an external load when
- A. the load resistance is much larger than the internal resistance
- B. the load resistance equals the internal resistance of the source
- C. the load resistance is zero
- D. the internal resistance is zero
Explanation
Matching the load to the internal resistance maximises the power delivered, though the efficiency at that point is only 50 per cent, since equal power is wasted inside the source. A power station therefore aims for high efficiency instead, keeping its internal resistance very low. Impedance matching in audio and radio systems is the same idea applied to alternating current.