Minimizing Series Resistance of Thermistor and LDR

Steps:

• Thermistors have high resistance when cold and low when hot.
• LDRs have high resistance in dark and low in light.
• Total resistance in series is sum of both components' resistances.
• Minimum total occurs when both individual resistances are lowest.

Why D is correct:

• Hot conditions minimize thermistor resistance (NTC type, per temperature-resistance curve); light minimizes LDR resistance (photoconductivity law), yielding lowest series total.

Why the others are wrong:

• A: Cold maximizes thermistor resistance; dark maximizes LDR resistance.
• B: Cold maximizes thermistor resistance, offsetting LDR decrease from light.
• C: Dark maximizes LDR resistance, offsetting thermistor decrease from hot.

Final answer: D