PhysicsAdvancedHigh School (11–12)Electricity & Magnetism › Current ElectricityNEETAEEE (Amrita)AMUEEEAP EAPCETBCECECMI Entrance
Created by StemPy LabAssertion (A): A copper wire is joined to a source that keeps the electric field in the wire the same. The wire is then heated. The drift speed of its free electrons increases. Reason (R): The relaxation time of the free electrons in a metal falls as the temperature rises, because the ions vibrate more strongly.
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← Five statements about resistance and temperature are given. (i) The resistivity of copper rises almost uniformly with temperature near room temperature. (ii) The resistivity of nichrome changes only slightly over a wide range of temperature. (iii) A metal's resistivity rises on heating because it has fewer free electrons. (iv) A 10 Ω copper wire at 20 °C becomes 13.2 Ω at 100 °C, for α = 4.0 × 10⁻³ °C⁻¹. (v) A semiconductor's resistivity falls on heating because its collisions become rarer. How many are correct?Assertion (A): A student connects a variable resistor of resistance R across a cell of fixed emf E and internal resistance r, and changes R from zero to a very large value. The power dissipated in the resistor is greatest when R = r. Reason (R): The current drawn from the cell is the largest when R = r. →
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