In the circuit shown above, R2 = 3R1 and the battery of emf ξ has negligible internal resistance. The resistance of the diode when it allows current to pass through it is also negligible. At time t = 0, the switch S is closed and the currents and voltage are allowed to reach their asymptotic values. Then at time t1, the switch is opened. Which of the following curves most nearly represents the potential at point A as a function of time t?
(GR8677 #94)
Solution:
When the switch is closed, at time t = 0, the voltage drops through the circuit. Thus, C, D and E are FALSE.
The time constant in the first process:
The time constant, τ is the time it takes the voltage across the component to either decrease or increase.
When the switch is opened, at time t1, the voltage increases with the time constant:
Thus,
It means, it takes less time for the voltage to increase than decrease.
Answer: B
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