Internal resistance and load affect current and terminal voltage

Steps:

• Initial: total resistance = 2 Ω + 1 Ω = 3 Ω; I = E/3; V = I × 2 Ω = 2I; E = V + I × 1 Ω = 3I.
• New: total resistance = 4 Ω + 1 Ω = 5 Ω; new current = E/5 = 3I/5 = 0.6I.
• New terminal p.d. = new current × 4 Ω = 0.6I × 4 = 2.4I.
• Initial V = 2I, so new p.d. = 2.4I = 1.2V.

Why B is correct:

• Ohm's law applied to total circuit resistance and terminal voltage formula V = E - Ir yield 0.6I and 1.2V exactly.

Why the others are wrong:

• A: Assumes current halves with doubled load (ignoring internal r), but terminal p.d. stays V, not 1.0V.
• C: 0.8I misapplies ratio as 4/5 (fraction of emf across load), not actual current.
• D: Same error as C, with extra decimal; current is 3/5 I = 0.6I, not 0.80I.

Final answer: B