# Homework Help: To solve ISRO paper, Can I post my doubt questions here in this thread

1. Mar 13, 2013

### dexterdev

I have a multiple choice question paper from ISRO 2012.

http://www.isro.org/pdf/EC-2012.pdf [Broken]

Can I post doubtful questions in this thread. Is there someone to help me.

-Devanand T

Last edited by a moderator: May 6, 2017
2. Mar 13, 2013

### Staff: Mentor

I think as long as you post about just one question at a time, and list the Relevant Equations and show your sincere Attempt at a Solution, it should be okay to do for now.

Last edited by a moderator: May 6, 2017
3. Mar 13, 2013

### dexterdev

Thank you sir, I will do that..

4. Mar 13, 2013

### Staff: Mentor

Which question do you want to tackle first?

5. Mar 13, 2013

### dexterdev

The circuit diagram is shown in the attached file..q18

The question 18 is regarding harmonics of current wave in the ac circuit having diodes.

My answer if option (a) , any mistake here..

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Last edited: Mar 13, 2013
6. Mar 14, 2013

### Staff: Mentor

I don't think we can assume ideal or idealized diodes here, for the simple reason that if the source is an ideal sinusoid, and the diodes were to drop a fixed 0.6V, then where does the remainder of the voltage disappear?

So I picture operation over the diode's exponential curve (which extends to infinity), and giving rise to a distorted alternating current (perhaps missing a portion around the zero crossings).

Being a distorted sinewave, it contains harmonics.

7. Mar 14, 2013

### dexterdev

Ok thankyou sir , will come with other doubts in the same paper..

8. Mar 14, 2013

### Staff: Mentor

I haven't answered the question, apart from ruling out (a).

9. Mar 14, 2013

### dexterdev

sorry

10. Mar 14, 2013

### dexterdev

As diode is having a nonlinear behaviour can we say the output is like
I = a + b v^1 + c v^2 + d v^3 + .............

so will all harmonics come...

11. Mar 14, 2013

### Staff: Mentor

I don't think so. I think you should try to sketch the expected current waveform.

12. Mar 14, 2013

### dexterdev

ok I will try.

13. Mar 17, 2013

### dexterdev

7th question

Hi pf,
Please see the attached figured , it is the 7th question.

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