50V battery is supplying current of 10 amp when connected to a resistor. If the efficiency of battery at this current is 25%. Then internal resistance of battery is :
50 = 10[R + r]
The correct answer is: 3.75Ω
A cell of emf E having an internal resistance ‘r’ is connected to an external resistance R. The potential difference ‘V’ across the resistance R varies with R as shown by the curve :
The correct answer is: B
‘n’ identical light bulbs, each designed to draw P power from a certain voltage supply are joined in series and that combination is connected across that supply. The power consumed by one bulb will be :
For series combination, the total power is:
1/P_{t} = 1/P_{1} + 1/P_{2} +.........+1/P_{n}
= 1/P + 1/P +..............+ upto n
= n/P
Therefore, P_{t} = P/n
A copper sphere of 10cm diameter is lowered into a water filled hemispherical copper vessel of 20cm diameter so that the sphere and the vessel becomes concentric. Electrical conductivity of water of σ = 10^{3}(Ωm)^{1}. The electrical resistance between the sphere and the vessel is :
The arrangement is shown in figure. Consider the hemispherical shell of radius r and thickness dr as shown.
The correct answer is: 1591.6Ω
When a galvanometer is shunted with a 4Ω resistance, the deflection is reduced to onefifth. If the galvanometer is further shunted with a 2Ω wire, the further reduction (find the ratio of decrease in current to the previous current) in the deflection will be (the main current remains the same).
Case I
Case II
so decrease in current to previous current
The correct answer is: (8/13) of the deflection when shunted with 4Ω only
In the circuit shown, the value of R in ohm that will result in no current through the 30V battery, is:]
Potential drop across R = Potential drop across AB
The correct answer is: 30Ω
In the shown wire frame, each side of a square (the smallest square) has a resistance R. The equivalent resistance of the circuit between the points A and B is :
Hence equivalent resistance between A and B is 2R.
The correct answer is: 2R
Two long coaxial and conducting cylinders of radius a and b are separated by a material of conductivity σ and a constant potential difference V is maintained between them, by a battery. Then the current, per unit length of the cylinder flowing from one cylinder the other is:
where is the linear charge density on the inner cylinder
Current per unit length will be :
A cylindrical solid of length L and radius a is having varying resistivity given by ρ = ρ_{0}x where ρ_{0} is a positive constant and x is measured from left end of solid. The cell shown in the figure is having emf V and negligible internal resistance. The electric field as a function of x is best described by :
Consider an elemental part of solid at a distance x from left end of width dx.
Resistance of this elemental part is,
Current through cylinder is,
Potential drop across element is,
In a practical wheat stone bridge circuit as shown, when one more resistance of 100Ω is connected is parallel with unknown resistance x, then ratio ℓ_{1}/ℓ_{2} become 2, ℓ_{1} is balance length. AB is a uniform wire. Then value of x must be :
∵ wheat stone bridge is in balanced condition
The correct answer is: 100Ω
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