In a closed circuit, the current I (in ampere) at an instant of time t (in second) is given by I = 4 − 0.08 t. The number of electrons flowing in 50 s through the cross- section of the conductor is

• 1.25 × 10¹⁹ 

• 6.25 × 10²⁰

• 5.25 × 10¹⁹

• 2.55 × 10²⁰

If R₁ and R₂ be the resistances of the filaments of 200 W and 100 W electric bulbs operating at 220 V, then $\left(\frac{{\mathrm{R}}_1}{{\mathrm{R}}_2}\right)$ is

• 1

• 2

• 0.5

• 4

A potentiometer wire, 10 m long, has a resistance of 40 Ω. It is connected in series with a resistance box and a 2 V storage cell. If the potential gradient along the wire is (0.1 mV / cm), the resistance unplungged in the box is

• 260 Ω

• 760 Ω

• 960 Ω

• 1060 Ω

44.

When a current I flows through a wire, the drift velocity of the electrons is v. When current 2I flows through another wire of the same material having double the length and double the area of cross-section, the drift velocity of the electrons will be

• $\frac{\mathrm{v}}{8}$

• $\frac{\mathrm{v}}{4}$

• $\frac{\mathrm{v}}{2}$

• v

A uniform electric field and a uniform magnetic field exist in a region in the same direction. An electron is projected with a velocity pointed in the same direction. Then the electron will 

• be deflected to the left without increase in speed

• be deflected to the right without increase in speed

• not be deflected but its speed will decrease

• not be deflected but its speed will increase

A galvanometer of resistance 20 Ω shows a deflection of 10 division when a current of 1 mA is passed through it. If a shunt of 4 Ω is connected and there are 50 division on the scale, the range of the galvanometer is

• 1 A

• 3 A

• 30 mA

• 30 A

A conducting rod of 1 m length and 1 kg mass is suspended by two vertical wires through its ends. An external magnetic field of 2 T is applied normal to the rod. Now the current to be passed through the rod so as to make the tension in the wires zero is [Take g = 10 ms^-2]

• 0.5 A

• 15 A

• 5 A

• 1.5 A

A circular coil of 5 turns and of 10 cm mean diameter is connected to a voltage source. If the resistance of the coil is 10 Ω, the voltage of the source so as to nullify the horizontal component of earth's magnetic field of 30 A turn m^-1 at the centre of the coil should be

• 6 V, plane of the coil normal to magnetic meridian

• 2 V, plane of the coil normal to magnetic meridian

• 6 V, plane of the coil along the magnetic meridian

• 2 V, plane of the coil along the magnetic meridian

A paramagnetic substance of susceptibility 3 x 10^-4 is placed in a magnetic field of 4 x10 Am^-1. Then the intensity of magnetization in the units of Am^-1 is

• 1.33 × 10⁸

• 0.75 × 10^-8

• 12 × 10^-8

• 14 × 10^-8

A square coil of side 25 cm having 1000 turns is rotated with a uniform speed in a magnetic field about an axis perpendicular to the direction of the field. At an instant t, the emf induced in the coil is e = 200 sin 100 πt. The magnetic induction is

• 0.50 T

• 0.02 T

• 0.01 T

• 0.1 T