A potentiometer has uniform potential gradient. The specific resistance of the material of the potentiometer wire is 10^-7 ohm-metre and the current passing through it is 0.1 ampere, cross-section of the wire is 10^-6 m². The potential gradient along the potentiometer wire is

• 10^-6 V/m

• 10^-4 V/m

• 10^-8 V/m

• 10^-2 V/m

A fuse wire with radius 1 mm blows at 1.5 ampere. The radius of the fuse wire of the same material to blow at 3A will be

• 3^1/4 mm

• 4^1/3 mm

• 3^1/2 mm

• 2^1/3 mm

A wire in the form of a circular loop of one turn carrying a current produces a magnetic field B at the centre. If the same wire is looped into a coil of two turns and carries the same current, the new value of magnetic induction at the centre is

• 3B

• 5B

• 4B

• 2B

34.

To send 10% of the main current through a moving coil galvanometer of resistance 99 ohm, the shunt required is

• 10 ohm

• 9.9 ohm

• 9 ohm

• 11 ohm

The magnetic flux linked with a coil at any instant 't' is given by $\mathrm{\varphi } = 5{\mathrm{t}}^3 - 100\mathrm{t} + 300$ the emf induced in the coil at t = 2 second is

• 40 V

• − 40 V

• 300 V

• 140 V

A charged particles moves along the line AB which lies in the same plane of a circular loop of conducting wire as shown in the figure. Then

• no current will be induced in the loop

• the current induced in the loop will change its direction as the charged particle passes by

• the current induced will be anti-clockwise

• the current induced will be clockwise

The time taken by AC of 50 Hz in reaching from zero to the maximum value is

• 50 × 10^-3 sec

• 5 × 10^-3 sec

• 1 × 10^-3 sec

• 2 × 10^-3 sec

The ratio of the secondary to the primary turns in a transformer is 3 : 2 and the output power is P. Neglecting all power losses, the input power must be

• $\frac{\mathrm{P}}{2}$

• P

• $\frac{2\mathrm{P}}{3}$

• $\frac{3\mathrm{P}}{2}$

The material used for permanent magnet has

• low retentivity, high coercivity

• high retentivity, low coercivity

• high retentivity, high coercivity

• low retentivity, low coercivity

A fish, looking up through the water sees the outside world contained in a circular horizon. If the refractive index of water is 4/3 and the fish is 12 cm below the surface of water, the radius of the circle in centimetre is

• $\frac{12 \times 3}{\sqrt{5}}$

• $12 \times 3 \times \sqrt{5}$

• $\frac{12 \times 3}{\sqrt{7}}$

• $12 \times 3 \times \sqrt{17}$