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Alternating Current — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsAlternating Current1 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: An electric lamp connected in series with a variable capacitor and A.C. source, its brightness increases with increase in capacitance.
Reason: Capacitive reactance decreases with increase in capacitance of capacitor.
✓

Answer

  1. Both A and R are true and R is the correct explanation of A.
Explanation:

Capacitive reactance $\text{X}_\text{C}=\frac{1}{\omega\text{C}}.$ When roe capacitance C increases, the capacitive reactance decreases. Due to decrease in its values, the current in the circuit will increase $\Bigg(\text{I}=\frac{\text{E}}{\sqrt{\text{R}^2+\text{X}^2_\text{C}}}\Bigg)$ and hence brightness of source (or electric lamp) will also increases.

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