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In the circuit shown switch is closed at t = 0. The time constant of the circuit is :

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NIELIT Scientific Assistant ECE 5 Dec 2021 Official Paper
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  1. 12 sec 
  2. 1.2 sec
  3. 10 sec 
  4. 6/7 sec

Answer (Detailed Solution Below)

Option 1 : 12 sec 
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Detailed Solution

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Concept:

The time constant (τ) of an RC circuit is given by the formula:

τ = ReqC

where Req is the equivalent resistance seen by the capacitor, and C is the capacitance.

While finding out the time constant the voltage source will be shorted.

Calculation:

Given:

Resistors: 3Ω and 2Ω will be in parallel
Capacitance: C = 10 F

Solution:

If the resistors are actually in parallel (common in RC circuits):

Req = (3Ω × 2Ω)/(3Ω + 2Ω) = 6/5Ω = 1.2Ω

τ = ReqC = 1.2Ω × 10 F = 12 sec

Final Answer:

The correct time constant is 1) 12 sec when considering parallel resistors.

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-> NIELIT Scientific Assistant city intimation slip 2025 has been released at the official website.

-> NIELIT Scientific Assistant exam 2025 is scheduled to be conducted on June 28. 

-> A total number of 113 revised vacancies have been announced for the post of Scientific Assistant in Computer Science (CS), Information Technology (IT), and Electronics & Communication (EC) streams.

-> Online application form, last date has been extended up to from 17th April 2025.

->The NIELT has revised the Essential Qualifications for the post of Scientific Assistant. Candidates must possess (M.Sc.)/ (MS)/ (MCA) / (B.E.)/ (B.Tech) in relevant disciplines.

 

-> The NIELIT Scientific Assistant 2025 Notification has been released by the National Institute of Electronics and Information Technology (NIELIT).

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