Solved Numerical Problem No. 18.2 ( Unit-18: Electronics); HSSC-II (Class-12); Physics (Punjab Curriculum and Text Board, Lahore) With Verified Answers

Fig.P.18.2 shows a transistor that operates a relay as the switch S is closed. The relay is energized by a current of 10 mA. Calculate the value R, which will just make the relay operate. The current gain β of the transistor is 200. When the transistor conducts, its `\V_{BC}` can be assumed to be 0.6 V. (Ans: 168 kΩ)

Given:

Collector Current = `\I_C` =  10 mA = 10 ｘ10⁻³ A

Current gain = β = 200

Voltage at Base Current = `\V_{B_C}` =  0.6 V

Voltage at Collector Current = `\V_{C_C}` =  9 V (given in the Figure)

To Find:

Resistance at Base = `\R_B` =  ?

Solution:

We know that

`\V_{C_C}` = `\I_B` `\R_B`  +  `\V_{B_C}`

or 

`\R_B` = `\frac {V_{C_C} - V_{B_C} }{I_B}` -----------(1)

where `\I_B` is unknown and can be calculated from the gain formula

β = `\frac {I_C}{I_B}`

or

`\I_B` = `\frac {I_C}{β}`

putting values

`\I_B` = `\frac {10 ｘ10⁻³ A}{200}`

`\I_B`  = 0.05ｘ10⁻³ A 

Now putting the corresponding values in equation (1)

`\R_B` = `\frac {9 V - 0.6 V }{0.05ｘ10⁻³ A}`

`\R_B` = `\frac {8.4 V }{0.05ｘ10⁻³ A}`

`\R_B` = 168ｘ10³ Ω 

or

`\R_B` = 168 KΩ -------------Ans.

************************************

Shortcut Links For 

1. National MDCAT, ECAT, JOB EXAM Physics MCQs Preparation (New) 
2. Physics (New) 11th Class SLO Based Notes
3. Physics (New) 11th class MCQs Quizzes All Units
4. Physics (New) 12th Class SLO Based Notes
5. Physics (New) 12th class MCQs Quizzes All Units

1. Website for School and College Level Physics   

(https://askrarequiz.blogspot.com)

2. Website for School and College Level Mathematics  

(https://askraremaths.blogspot.com)

3. Website for Single National Curriculum Pakistan - All Subjects Notes 

(https://askrareclassnotes.blogspot.com/)

© 2022-Onwards by Academic Skills and Knowledge (ASK)     

Note:  Write me in the comment box below for any query and also Share this information with your class-fellows and friends.