# SSC JEÂ  Electrical Conventional Paper with Explained SolutionÂ 2015 | MES Electrical

Ques 1(a).Â A copper wire has a resistance of 0.85Î© at 20Â°C. What will be its resistance at 40Â°C? The temperature coefficient of resistance of copper at 0Â°C is 0.004Â°C.

Answer.Â  Resistance Temperature Coefficient

RtÂ  =Â Ro(1 +Â Î±ot)

Where

RoÂ is the resistance at 0Â° Celsius

RtÂ is the Resistance at tÂ° Celsius.

Given Rt =Â 0.85Î© at 20Â°C

Temperature coefficient of resistanceÂ Î± = 0.04Â°C

tÂ = 20Â°

Ro = ?

0.85 =Â Ro [ 1 + 0.004 Ã— 20]

0.85 =Â RoÃ—1.08

Ro = 0.787Â Î©

Now the resistance of the copper at 40Â°C

RtÂ  =Â Ro(1 +Â Î±ot)

Given Rt =Â ? at 40Â°C

Temperature coefficient of resistanceÂ Î± = 0.04Â°C

tÂ = 20Â°

Ro = 0.787 Î©

Rt =Â 0.787 [ 1 + 0.004 Ã— 40]

Ques 1(b).Â In the circuit shown in figure what is the value of VB?

Answer:- In the above figure the two voltage sources are connected in series therefore there equivalentÂ voltage will be (V1 + V2)

Then the total voltage in the given question will be

[V1 + (âˆ’V2)] = (6Â âˆ’ 5) = 1V

Veq = IR

Or IR = 1

Now potential difference across the resistorÂ

VAÂ âˆ’ VB = IR

6Â âˆ’ VB = 1

âˆ´ VB = 5V

Ques 1(c).Â What is the value of Thevenin voltage ETH in the given circuit as shown in the figure?

Answer:–Â  As per Thevenin theorem, when resistance RL is connected across terminals A and B, the network behaves as a source of voltage ETh and internal resistance RT and this is called Thevenin equivalent circuit.

Thevenin Voltage

The Thevenin voltage e used in Thevenin’s Theorem is an ideal voltage source equal to the open circuit voltage at the terminals. In the given question, the resistance 1Î© does not affect this voltage and the resistances 3Î© and 7Î©Â form a voltage divider, giving

$\begin{array}{l}{E_{Th}} = 50 \times \dfrac{7}{{7 + 3}}\\\\{E_{TH}} = 35V\end{array}$

Ques 1(d):-Â In figure find the value of resistance R

Applying KCL at Node “1”

$\dfrac{{{V_1} - 100}}{{10}} + \dfrac{{{V_1}}}{{10}} + 2 = 0$

2V1Â âˆ’ 100 + 20 = 0

2V1 = 80

V1 = 40 V

R = V1/I = 40/2 = 20Î©

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