JEE Main · 2020 · 03 Sep 2020 · Shift 1 · Current Electricity

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When a diode is forward biased, it has a voltage drop of 0.5 V. The safe limit of current through the diode is 10 mA. If a battery of emf 1.5 V is used in the circuit, the value of minimum resistance to be connected in series with the diode so that the current does not exceed the safe limit is

(A) $100Ω$ ✓ Correct
(B) $200Ω$
(C) $50Ω$
(D) $300Ω$

Answer: (A)

Solution

Going round the loop, the battery emf equals the diode drop plus the drop across the resistor:

1.5 = 0.5 + I R

. At the safe limit

I = 10

= 0.01

A, so

R = \frac{1.5 - 0.5}{0.01} = 100 Ω

, and this is the minimum resistance that keeps the current from exceeding the limit.

JEE Main · 2020 · 03 Sep 2020 · Shift 1 · Single correct option

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