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Q1 Sometimes it is said that "heat is developed in" in a resistance when there is electric current in it. Recall heat is defined as energy due to temperature difference. Is the statement under quotes technically correct? Q2 When a current is estabished in a wire, the free electrons drift in the direction opposite to the current. Does the number of free electrons in a wire continuously decrease?


Q1 Sometimes it is said that "heat is developed in" in a resistance when there is electric current in it. Recall heat is defined as energy due to temperature difference. Is the statement under quotes technically correct?


Q2 When a current is estabished in a wire, the free electrons drift in the direction opposite to the current. Does the number of free electrons in a wire continuously decrease?


Grade:12

1 Answers

SAGAR SINGH - IIT DELHI
879 Points
10 years ago

Dear nikhil,

When a charge moves in a conductor, work is done by that charge. Devices can be made which convert this work into heat ( electric heaters), light (light bulbs and neon tubes), or motion, i.e. kinetic energy (power tools).

From the definition of potential difference, V, we have V = W/Q, where W is the work done by charge Q. Hence, W = VQ.

Current is the flow of charge, so that in time t, the amount of charge moving through the conductor will be Q = It.

Therefore, W = VIt gives the work done in time t, by a current I, flowing through a conductor across which the potential difference is V. This may be written in two other ways by substituting from Ohm's Law:

W = V²t/R

where R is the resistance of the conductor.

 

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