Choose efficiency instead of peak power

A model source has emf 10 V and internal resistance 2 Ω. It supplies one positive load resistor. Require 75% of the ideal source’s converted power to reach the load.

What load resistance meets this efficiency?

Organize the givens & assumptions

Emf: 10 V
Internal resistance: 2 Ω
Required load fraction: 0.75

Constant ideal emf and positive Ohmic internal resistance over the stated interval; settled DC currents and negligible lead resistance. This is an assigned source model, not battery test data. Efficiency counts only internal resistive loss.

A $1.5\ \Omega$
B $8\ \Omega$
C $6\ \Omega$
D $2\ \Omega$

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