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Current Electricity — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsCurrent Electricity1 Mark
Question
For two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true, and R is the correct explanation of A.
  2. Both A and R are true, but R is not the correct explanation of A.
  3. A is true, but R is false.
  4. A is false, and R is also false.
Assertion: Fuse wire must have high resistance and low melting point.
Reason: Fuse is used for small current flow only.
✓

Answer

  1. A is true, but R is false.
Explanation:

Fuse wire must have high resistance because in series, current remains same. Therefore according to Joule's law $\text{H}=\frac{\text{i}^2\text{Rt}}{4.2},$ heat produced is high if R is high. The melting point must be low so that wire may melt with increase in temperature. As a current larger than the specified value flows through the circuit the temperature of the fuse wire increases. This melts the fuse wire and breaks the circuit.

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