Question

The resistance of pure metallic conductor ____________ with the ____________ in temperature. (a) increases, increase (b) increases, decrease (c) remains same, increase (d) remains same, decrease

Answer 1

Hi Mate!!!

On increasing temperature relaxation time decrease and hence resistance increases.

So,. a part is correct one.


Have a great day..

Answer 2

option a
what is the effect on the resistance of metallic wire if temperature increased?

Answer

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9 ANSWERS



Apramey Mishra, ECE

Updated Jul 10, 2016

I will explain this in two parts theoretically and simply:
1.Behavior of metal at normal temp
2.Behavior of metal at high temp
 
Consider an electron in a wire /conductor under the influence of electric field (or due to application of voltage in a circuit), a current will be generated in the direction opposite to the direction of movement of the electron. So assume this electron is travelling from -ve potential to +ve potential (or from -ve battery terminal to +ve terminal.
 
CASE I: Without application of heat.(or at lower temperatures)
This is a free electron in the wire, but not all electrons are free to move in the internal lattice structure, there are obstacles (immobile ions / electrons)which pose hindrance to the movement of this electron. So the electron moves in a zig zag (random) path colliding/bouncing here and there with the obstacles to reach the +ve terminal of the battery. The avg. velocity of this electron is called drift velocity (this is same as non uniform motion velocity i.e. where velocity=u +at) and the time taken between successive collisions is called relaxation period. At normal temp. the time between successive collisions is more because the obstacles are usually at rest(or very less mobile). So relaxation period is large and hence the drift velocity is largeas drift velocity is proportional to relaxation time.



Now coming to the point of resistance. The resistance is inversely proportional to the drift velocity so more the drift velocity lesser is the resistance.
 
CASE II: With application of heat.(or at higher temperatures)
In this case, due to the energy from heat few immobile electrons become free electrons ,also the obstacles (immobile ions/electrons)which pose hindrance to the movement of the free electron start to vibrate (become slightly more mobile) due to energy gained by the heat. So the electron moves in a more zig-zag (random) and unorganized path colliding/bouncing more and more because of more number of electron and other obstacles to reach the +ve terminal of the battery. At high temp. the time between successive collisions is less because the obstacles are usually vibrating(or slightly more mobile). So relaxation period is less and hence the drift velocity is less as drift velocity= (acceleration * relaxation period).
Now coming to the point of resistance. The resistance is inversely proportional to the drift velocity so less the drift velocity more is the resistance. Hence the resistance increases.



CONCLUSION: higher the temperature more is the unorganized movement and more is the number of collisions and thus harder for the free electron to reach its destination and hence higher is the resistance