Question:
The quantities that don't change when a resistor connected to a battery is heated due to the current are:
(A) Drift speed
(B) Resistivity
(C) Resistance
(D) Number of free electrons
The quantities that don't change when a resistor connected to a battery is heated due to the current are:
(A) Drift speed (B) Resistivity (C) Resistance (D) Number of free electrons
(A) Drift speed (B) Resistivity (C) Resistance (D) Number of free electrons
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In metallic conductors, heating increases resistivity and resistance, but the number of free electrons remains approximately constant.
Updated On: Jun 24, 2026
- B and C
- D
- A
- A and D
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The Correct Option is B
Solution and Explanation
Step 1: Analyze the effect of heating on resistivity.
For metallic conductors, resistivity increases with temperature.
Hence, Resistivity changes. Therefore, (B) is not correct.
Step 2: Analyze the effect on resistance.
Resistance is given by \[ R=\rho \frac{L}{A} \] Since resistivity \[ \rho \] changes with temperature, resistance also changes.
Hence, (C) is not correct.
Step 3: Analyze the effect on drift speed.
Drift speed is \[ v_d=\frac{I}{neA} \] When the resistor is heated, resistance increases, causing current to decrease for a constant battery voltage. Thus drift speed also changes.
Hence, (A) is not correct.
Step 4: Analyze the number of free electrons.
Heating a metallic conductor does not significantly change the number density of free electrons.
Therefore, Number of free electrons remains unchanged. Hence, (D) is correct.
Step 5: Final conclusion.
Therefore, the quantity that does not change is \[ \boxed{\text{D}} \]
For metallic conductors, resistivity increases with temperature.
Hence, Resistivity changes. Therefore, (B) is not correct.
Step 2: Analyze the effect on resistance.
Resistance is given by \[ R=\rho \frac{L}{A} \] Since resistivity \[ \rho \] changes with temperature, resistance also changes.
Hence, (C) is not correct.
Step 3: Analyze the effect on drift speed.
Drift speed is \[ v_d=\frac{I}{neA} \] When the resistor is heated, resistance increases, causing current to decrease for a constant battery voltage. Thus drift speed also changes.
Hence, (A) is not correct.
Step 4: Analyze the number of free electrons.
Heating a metallic conductor does not significantly change the number density of free electrons.
Therefore, Number of free electrons remains unchanged. Hence, (D) is correct.
Step 5: Final conclusion.
Therefore, the quantity that does not change is \[ \boxed{\text{D}} \]
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