Statement-1: Conductivity of a metallic conductor decreases with increase in temperature. Statement-2: On increasing temperature the number of free electrons in the metallic conductor decreases.
A
Statement-1 is true, Statement-2 is true; Statement-2 is a correct explanation for Statement-1
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B
Statement-1 is true, Statement-2 is true; Statement-2 is NOT a correct explanation for Statement-1
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C
Statement-1 is true, Statement-2 is false
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D
Statement-1 is false, Statement-2 is true
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Solution
The correct option is CStatement-1 is true, Statement-2 is false For conductor, we know that resistivity (ρ) increases with temperature
⇒T↑ρ↑
∴σ=1ρ↓
Resistance of the metallic wire increases with rise in temperature. If resistance increases conductivity decreases.
So, Statement-1 is true.
Number of free electrons in metals is not dependent on change in temperature.
Thus, Statement-2 is false.
Note : ρ=2mne2τ=1σ
σ is called conductivity and ρ is conductivity.
As temperature increases relaxation time τ decreases.
Resistivity increases and conductivity decreases.