Question

Question 5 a) A transformer has 500 turns on the primary and 1500 turns on the secondary. If the output voltage is 36 V what is the input voltage? What type of transformer is this? (3 marks) b) 100 kW is delivered to a town along power lines that have a total resistance of 0.40. Calculate the power loss if the electricity is delivered at a voltage of (l) 240 V and (ii) 24kV. (5 marks) c) If the collector current of a transistor is 0.3 amps and the base current is 0.001 amps, what is the current gain? (2 marks) Total 10 marks Space to answer Question 5 here

Answer 1

solution

(A)  

number of turn in a primary

(NP) = 500

number of turn in a secondary

(Ns) = 1500

secondary voltage (  
S
) =      

primary voltage ($V_{P}$) $=V_{in}$ =  ?

now we know that

$\frac{N_{S}}{N_{P}}= \frac{V_{S}}{V_{P}}$

$\frac{1500}{500}= \frac{36}{V_{in}}$

now so it is step up transformer

(B)

we have a resistance (R) = 0.4 Ohm

delivered power to a town =100000 W

(i) if the power delivered at a 240 V so

delivered power   $=V_{1}I_{1}$  

$100000 = 240 \times I_{1}$

$I_{1}=\frac{ 10^{4}}{24}A$

then power loss at a 240V voltage  

$\frac{ (10^{4})^{2}}{24^{2}}\times 0.4$

$=6.94 \times 10 ^{4} W$

(ii) if the power delivered at a 24kV so

delivered power

$100000=24000\times I_{2}$

$I_{2} = \frac{100}{24 }A$

then power loss at a 24kV voltage

$(\frac{100}{24})^{2} 0.4$

(C)

  $\beta = \frac{I_{C}}{I_{B}}$   

$\beta$    is voltage gain\

$\beta = \frac{0.3}{0.001}$  

and current gain is define as

$\alpha =\frac{\beta }{1+\beta }$

$\beta = \frac{300}{1+300}$

$\beta = 0.9966$