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Physics · 2024 · 2 marks
Current ElectricityDrift of Electrons and the Origin of Resistivity2 marksUnderstandvery short answer
CBSE 2024 · Region 2 · Set 2 · Q17
(a) "The electron drift speed is only a few mm / s for currents in the range of a few amperes for a given conductor." How then is current established…
(a)
"The electron drift speed is only a few $\displaystyle \mathrm{mm} / \mathrm{s}$ for currents in the range of a few amperes for a given conductor." How then is current established almost the instant a circuit is closed ? Explain.
(b)
' $\displaystyle \mathrm{V}=\mathrm{IR}$ is a statement of Ohm's Law' is not true. Explain.
Marking-scheme solution
(a)
An electric field is established throughout the circuit almost instantly. It causes a local electron drift at every point, so the establishment of current does not have to wait for electrons from one end of the conductor to travel to the other end.
(b)
Ohm's law asserts that the plot of I versus V is linear, i.e. R is independent of V, while the equation $\displaystyle V=I R$ defines resistance and it may be applied to all conducting devices whether they obey Ohm's law or not.
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