281.

Kirchhoff's law of junction, ΣI = 0, is based on

• conservation of energy

• conservation of charge

• conservation of energy as well as charge

• conservation of momentum

A battery of emf 10 V and internal resistance of 0.5 ohm is connected across a variable resistance R. The maximum value of R is given by

• 0.5 Ω

• 1.00 Ω

• 2.0 Ω

• 0.25 Ω

The internal resistance of a primary cell is 42. It generates a current of 0.2 A in an external resistance of 21 n. The rate at which chemical energy to consumed in providing current is

• 1 J/s

• 5 J/s

• 0.42 J/s

• 0.8 J/s

The equivalent resistance across A and B is

• 2 Ω

• 3 Ω

• 4 Ω

• 5 Ω

At room temperature, copper has free electron density of 8.4 x 10²⁸ m^-3, The electron drift velocity in a copper conductor of cross-sectional area of 10^-6 m² and carrying a current of 5.4 A, will be

• 4 ms^-1

• 0.4 ms^-1

• 4 cm s^-1

• 0.4 mm s^-1

A uniform wire of resistance R and length L is cut into four equal parts, each of length  L/4 which are then connected in parallel combination. The effective resistance of the combination will be

• R

• 4R

• $\frac{\mathrm{R}}{4}$

• $\frac{\mathrm{R}}{16}$

A 5 amp fuse wire can withstand a maximum power of 1 W in circuit. The resistance of the fuse wire is

• 0.2 Ω

• 5 Ω

• 0.4 Ω

• 0.04 Ω

When plate voltage in diode valve is increased from 100V to 150V. Then, plate increases from 7.5 mA to 12 mA, then dynamic plate resistance will be

• 10 kΩ

• 11 kΩ

• 15 kΩ

• 11.1 kΩ

Find equivalent resistance between X and Y

• R

• R/L

• 2R

• 5R

A engine pumps up 100 kg of water through a height of 10 m in 5s. Given that, the efficiency of engine is 60%. If g = 10 ms^-2, the power of this engine is

• 3.3 kW

• 0.33 kW

• 0.033 kW

• 33 kW