# LOTS of Electrical Maths Problems

1. Jan 18, 2005

### fcukniles

I'm confused about quite a lot of this stuff i have numbered it so if you can help in any of them please post what number you are helping with!
thankyou.

1. Draw the equivalent circuit of an amplifier with an input resistance of 3 k, output
resistance 100 and unloaded voltage gain of 1000.

It is fed from a signal source which is a pressure transducer having a sensitivity of 1mV/Pa (1 Pa = 1 N/m2) and an output resistance of 1000. It drives a recorder having an input resistance of 500 and a full scale deflection of 2 V recorder input.

Calculate:

(i) the percentage recorder deflection when the pressure is 2 Pa [62.5%].

(ii) the following gains measured between the transducer and the recorder
terminals:

(a) voltage
(b) current, and
(c) power

2)6. You have two identical amplifiers, each having an open-circuit voltage gain of 100, an input resistance of 1k and an output resistance of 100. You propose to cascade them to produce a two-stage amplifier.

Draw the "black-box" equivalent circuit of the arrangement, including an ideal voltage source for the input and assuming an open-circuit output.
Calculate the overall voltage gain from the input of the first amp to the output of the second.

You now find that, in practice, your source has an internal resistance of 1k and the output load is 50
Draw the new "black-box" equivalent circuit of the arrangement, and calculate the new overall voltage gain from the input of the first amp to the output of the second.

If you didn't know better, you might think that the overall gain would be
100 x 100 = 10 000. Why is the actual gain only about one-third of this?

3)(a) Explain the principal characteristics of an operational amplifier.
(b) Compare the functions of an ‘inverting’ and ‘noninverting’ operational
amplifier.
(c) Briefly explained how a summing amplifier may be used as a digital to analogue converter.

4)
Draw the block diagrams of operational amplifiers suitable for performing the
following mathematical functions.

(a) vo = -5vin (b) vo = -(3v1 + 2v2)
(c) vo = 10v1 - v2 (d) vo = 6 v1 dt.

Thanks for any help...you guys are about 10000x more helpful than my teacher who says 'look in you book stop bothering me!' if only the book wasnt ****!

2. Jan 18, 2005

### brewnog

You should listen to your teacher!

Show us what you've done (rather than expecting someone to do your homework for you) and wait for it to be moved to the Homework section.

3. Jan 18, 2005

### fcukniles

this isn't homework, i've got a exam this week am just clearing up things i dont understand, i have got a list of answers just not sure how to come about them

4. Jan 18, 2005

### fcukniles

i realise there is a lot there sorry but any help for them would be much apricated
thnx guys

5. Jan 18, 2005

### fcukniles

got a exam tomorrow afternoon if anyone could help b4 then would be class thanks

6. Jan 22, 2005

### Theelectricchild

You need to explain your reasoning nevertheless... we have no incentive to help if you do not explain your methods... and the reason is, a person just cannot learn from people if the person helping does not understand the student's weakness.

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