# Electrical Problems

Hi

I hope you can help me with these few questions,

I have made some attempts myself.

On question 1 I have assumed a supply voltage of 28volts.

That is If this is what the question means.

The text book is HUGHES electrical and electronic technology

(1) A zener diode has a reverse breakdown voltage of 14V with a maximum load current of 70mA calculate a suitable value of limiting resistance

L Res = VIN - ZD1 L Res = 28V - 14V = 200 ohms

IZD1 70 mA

(2) In a stabilisation circuit if the internal resistance is 8 ohms and the load current change is 60mA what is the value of Vs

This is in the question on the paper

And this is also in the text book

(Without stabilisation voltage can change a difference of 30V)

My attempt

S = change in stabilised voltage across load

Change in unstabilized voltage

S = Vs/30 0.016 =0.48V/30V

Ro = Vs/IL Ro= 0.48V/0.06=8ohms

Vs = 0.016x 30 = 0.48V

(3) A transistor amplifier in common-emitter mode has a gain of 25 if its ib 20uA what is the range of ic variation

I came up with

B = ic / ib

Ic = B x ib = 25 x 20uA=0.5mA

(4) A 100ohm resistor is placed across a 50v power source .If the source voltage is increased to 100v what is (A) the change in power (B) change in current and (C) change in terms of dB?

My Attempt

P1 = V1^2/ R = I1^2 x R 25W = 50V^2/100ohm = 0.5A^2 x 100ohm

P2 = V2^2/R = I2^2 x R 100W = 100v^2/100ohm = 1A^2 x 100ohm

(dB) =10log p2/p1 = 6dB

= 20log v2/v1 = 6dB

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