Impact of Rising Internal Resistance on Voltage and Power

Steps:

• Terminal potential difference V = E × (R / (R + r)), where E is e.m.f., R is external resistance, r is internal resistance; as r increases, V decreases.
• Current I = E / (R + r); as r increases, I decreases.
• Output power P = I²R; as I decreases, P decreases.

Why A is correct:

• Formulas V = E × R/(R + r) and P = [E/(R + r)]² × R show both V and P decrease as r increases, per Ohm's law for circuits with internal resistance.

Why the others are wrong:

• B: Output power decreases, not unchanged, since P depends on I which falls.
• C: Both terminal potential difference and output power decrease, not unchanged.
• D: Terminal potential difference decreases, not unchanged, as V = IR with I dropping.

Final answer: A