An LED has a rating of 2 V and 10 mA. If it is connected to a 6V battery, the minimum value of series resistance is

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ISRO VSSC Technical Assistant Electronics 2018 Official Paper
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  1. 40 Ω 
  2. 100 Ω 
  3. 200 Ω 
  4. 400 Ω 

Answer (Detailed Solution Below)

Option 4 : 400 Ω 
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Detailed Solution

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The given connection is represented with the help of the following diagram:

F1 S.B Madhu 23.03.20 D3

RS = Series LED resistance

For a minimum value of series resistance, the maximum current will flow through the LED.

Since, the maximum current rating of the LED = 10 mA, the minimum resistance for this maximum current can be calculated using KVL as:

6 - 2 - ImaxRS = 0

4 = 10m × RS

RS = 400 Ω

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