Unbalancing the potentiometer circuit to produce current through the ammeter

Steps:

• The zero ammeter reading indicates a balanced circuit where no current flows through the branch with the ammeter and LDR.
• The covered LDR has high resistance, maintaining balance at the current sliding contact position.
• Moving the sliding contact changes the potential divider ratio, altering the voltage across the LDR branch.
• A move to the right increases resistance in one arm, unbalancing the circuit and allowing current to flow.

Why C is correct:

• Moving the sliding contact right adjusts the potentiometer to mismatch the high LDR resistance, violating the balance condition (V1/V2 = R1/R2 in potential divider), causing current through the ammeter.

Why the others are wrong:

• A: Decreasing supply voltage reduces overall current but preserves balance, keeping ammeter at zero.
• B: Moving left likely maintains or reinforces balance for the high-resistance LDR, no current flows.
• D: Identical to C, but listed separately; no unique effect.

Final answer: C