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 :
Voltage across each bulb will be
so, power developed by each bulb = iV1 =
so, power consumed by one bulb =
The correct answer is: P/n2
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 one-fifth. 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).
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 = ρ0x where ρ0 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 ℓ1/ℓ2 become 2, ℓ1 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