| Directions: In the following questions, a statement of Assertion [A] is followed by a statement of Reason (R). |
| Mark the correct choice as: |
| Assertion [A]: An electric heater is heated first by direct and then by alternating currents. For both the currents, the potential difference across the ends of the heater is the same. The rate of production of heat will be different in two cases. |
| Reason (R): The resistance of a coil in alternating current will be more than the resistance of a coil in direct current, hence heat produced in case of direct current will be low. |
A) Both Assertion [A] and Reason (R) are true and Reason (R) is the correct explanation of Assertion [A]
B) Both Assertion [A] and Reason (R) are true but Reason (R) is not the correct explanation of Assertion [A]
C) Assertion [A] is true but Reason (R) is false
D) Assertion [A] is false and Reason (R) is also false
Correct Answer: A
Solution :
(a) The element of the heater is in the form of a coil so that it has inductance L also besides the resistance R. So, for the alternating current, the effective resistance of the heater would be \[\sqrt{{{R}^{2}}+{{(\omega L)}^{2}}}\] which is larger than the resistance R for the direct current. Hence on heating by alternating current, heat produced per second would be less. \[(H={{V}^{2}}/R\] and V is same in both the cases).
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