Parallel Resistors Alter Total Current and Terminal Voltage

Steps:

• Initial setup: Total resistance is internal r plus external R; current I = E/(r + R); voltmeter reads V = I × R across R.
• Adding identical R in parallel: Equivalent external resistance becomes R/2; total resistance decreases to r + R/2.
• Current increases: Smaller total resistance raises I to E/(r + R/2), so ammeter reading increases.
• Voltage decreases: New V = I × (R/2) = E × (R/2)/(r + R/2); larger effective denominator (2r + R) compared to original (r + R) lowers V.

Why C is correct:

• Ohm's law: Reduced total resistance increases current; more voltage drops across internal r, decreasing terminal voltage across external resistors (V = E × Req/(r + Req), where Req halves).

Why the others are wrong:

• A: Voltmeter decreases correctly, but ammeter increases, not decreases.
• B: Ammeter increases, not decreases; voltmeter decreases, not stays the same.
• D: Voltmeter decreases, not stays the same.

Final answer: C