Ques.81. If four 10μF capacitors are connected in parallel, the net capacitance is (SSC – 2010)
2.5 μF
40 μF
20 μF
15 μF
Answer.2. 40 μF
Explanation
If the capacitors are connected in parallel then their effective capacitance is
C = C1 + C2 + C3 —— Cn
Since 4 capacitors of 10μF are connected in parallel therefore
C = (10 + 10 + 10 + 10)μF = 40μF
Ques.82. The earth’s potential is taken as (SSC – 2010)
Infinite
Supply voltage
1 volt
Zero
Answer.4. Zero
Explanation:-
Why the electric potential of Earth is zero?
For the measurement of level, we have a standard or a zero level, that is sea level and for the measurement of temperature, a zero of temperature, that is the temperature of melting ice, so also for the measurement of potential, we must have a standard or a zero of potential. The potential of the earth is taken to be zero of potential. For this purpose, the earth has been chosen because of its huge size, so that the small charges with which we have to deal with, if given to it or taken from it, produce no change in its potential.
Thus, a body whose potential is higher than that of the earth is said to have positive potential and one whose potential is lower than that of the earth is said to have a negative potential
Ques.83. If Rg in the circuit shown in figure is variable between 20Ω and 80Ω then maximum power transferred to the load RL will be (SSC – 2010)
15 W
13.33 W
6.67 W
2.4 W
Answer.1. 15 W
Explanation:-
Rg = (20Ω to 80Ω)
Rg should be minimum to transfer maximum power to the load therefore we take
Rg = 20Ω
Hence I = V/(Rg + RL)
I = 40/80 = 0.5 A
Power transferred = I2RL
= (0.5)2 x 60 = 15 W
Ques.84. Time constant of the network shown in figure is (SSC – 2010)
2 RC
3 RC
RC/2
2RC/3
Answer.4. 2RC/3
Explanation:-
Req = (R x 2R)/(R + 2R)
= 2R/3
Time constant for RC circuit
Ques.85. A wire has a resistance 10Ω . It is stretched by one-tenth of its original length. Then its resistance will be (SSC – 2010)
10Ω
12.1Ω
9Ω
11Ω
Answer.2. 12.1Ω
Explanation:-
Resistance of a wire
R = ρl/A …………..1
where ρ is resistivity of the material
L is length in meters
A is cross-sectional area in m²
R’ = ρl’/A’……………..2
Now length of wire is stretched to 1/10 of its original length
l’ = l + l/10 = 11l/10
l’/l = 11/10
Since On stretching, Volume will be constant
lA = l’A’
A’/A = l/l’
from equation 1 & 2
R/R’ = lA’/l’A
R’ = R x 121/100
R’ = 1.21 x R = 1.21 x 10 = 12.1Ω
Ques.86. The value of current I flowing in the 1Ω resistor in the circuit shown in the figure below will be (SSC – 2009)
10A
6A
5A
0
Answer.3. 5A
Explanation:-
When only voltage source is present then voltage across 1Ω resistor is
V = 5V
I = V/R = 5/1 = 5A
Ques.87. In the figure shown below, if we connect a source of 2V, with internal resistance of 1Ω at AA’ with positive terminal at A, then the current through R is (SSC – 2009)
2A
1.66 A
1 A
0.625 A
Answer.4. 0.625 A
Explanation:-
Connect a source of 2V, with internal resistance of 1Ω at AA’
Applying Nodal analysis at C and B
Solving equation 1 & 2
VC = 1.125 Volt
VB = 1.25 Volt
Current through resistor R
IR = VB/2 = 1.25/2 = 0.625 A
Ques.88. The curve representing Ohm’s law is (SSC – 2009)
Linear
Hyperbolic
Parabolic
Triangular
Answer.1. Linear
Explanation:-
Ohm’s law of constant proportionality states that for a given conductor the ratio of voltage to current is constant i.e if the temperature, area, the length did not change the resulting current is directly proportional to the variation in the applied voltage. Hence the graph between voltage and current is linear. R(constant) = V/I
★Ohms law does not apply to all material it only applied to “linear” or “Ohmic Resistor”.
Ques.89. The specific resistance of a conductor depends upon (SSC – 2009)
The dimension of the conductor
Composition of conductor material
The resistance of the conductor
Both (a) and (b)
Answer.2. Composition of conductor material
Explanation:-
For any given material at a certain given temperature, the resistance is given as
where ρ is a constant depending on the nature of the material of the conductor and is known as its specific resistance or resistivity.
Specific Resistance depends only on temperature and material of the conductor but not on its dimensions of the conductor, on which resistance depends, and mechanical deformation such as stretching, etc. As ρ depends only on the material of a conductor at a given temperature, hence it is a characteristic constant.
Ques.90. Superposition theorem is essentially based on the concept of (SSC – 2009)
Reciprocity
Linearity
Duality
Non-linearity
Answer.2. Linearity
Explanation:-
According to superposition theorem
In any Linear and bilateral network consisting linear and bilateral and energy sources (e.g. generators), the current flowing at any point in the network is the algebraic sum of the currents those flow with each source were considered separately, with all the remaining source replaced at a time by their internal impedances.
The theorem is hence based on the linearity property and Ohm‘s law. The fundamental concept is that in linear impedance, for an increase in voltage across it, the current through it increases which is independent of the magnitude of the original current flowing through it.
