Thermistor current increases with temperature, calibrating ammeter scale accordingly

Steps:

• Assume constant voltage supply; total resistance is ammeter plus thermistor.
• Thermistor resistance R decreases as temperature T rises (NTC behavior from graph).
• Current I ≈ V/R increases with T, as ammeter resistance is negligible.
• Ammeter deflection rises with I, so temperature scale must increase along deflection direction.

Why A is correct:

• Matches I = V/R law: higher current corresponds to higher T on scale.

Why the others are wrong:

• B: Scale decreases with current, inverting I-T relation.
• C: Nonlinear scale mismatches typical R-T curve shape.
• D: Temperature decreases with deflection, opposing NTC decrease in R.

Final answer: A