Ohm's Law and Circuit Parameters with Changing Load

Steps:

• Denote cell e.m.f. as constant E; initial total resistance = 10.5Ω, current I₁ = E/10.5.
• New total resistance = 20.5Ω, current I₂ = E/20.5 ≈ I₁/2.
• Terminal p.d. V = I × external R; initial V₁ = I₁ × 10, new V₂ = I₂ × 20 > V₁.
• Power in resistor P = I² × R; initial P₁ = I₁² × 10, new P₂ = I₂² × 20 < P₁.

Why A is correct:

• e.m.f. E is an intrinsic property of the cell and remains unchanged regardless of external resistance.

Why the others are wrong:

• B: Current halves because total resistance roughly doubles (10.5Ω to 20.5Ω), so I ∝ 1/R.
• C: Power decreases as P ∝ I²R and I halves while R doubles, resulting in net reduction.
• D: Terminal p.d. increases toward E as external R rises, minimizing internal voltage drop (V = E × R/(R + r)).

Final answer: A