Two long straight wires are set parallel to each other. Each carries a current in the same direction and the separation between them is 2 r. The intensity of the magnetic field mid-way between them is

• $\frac{{\mathrm{\mu }}_0\mathrm{i}}{\mathrm{r}}$

• $\frac{4{\mathrm{\mu }}_0\mathrm{i}}{\mathrm{r}}$

• Zero

• $\frac{{\mathrm{\mu }}_0\mathrm{i}}{4\mathrm{r}}$

92.

A galvanometer of resistance 20 Ω is to be converted into an ammeter of range 1 A. If a current of 1 mA produces full scale deflection, the shunt required for the purpose is

• 0.01 Ω

• 0.05 Ω

• 0.02 Ω

• 0.04 Ω

A magnetic needle is kept in a non-uniform magnetic field. It experiences

• force and torque

• a force but not a torque

• a torque but not a force

• neither a force nor a torque

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

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

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

A magnet N-S is suspended from a spring and when it oscillates, the magnet moves in and out of the coil C. The coil is connected to a galvanometer G. Then, as the magnet oscillates

• G shows no deflection

• G shows deflection to the left and right but the amplitude steadily decreases.

• G shows deflection to the left and right with constant amplitude.

• G shows deflection on one side.

The maximum current that can be measured by a galvanometer of resistance 40 Ω, is 10 mA. It is converted into a voltmeter that can read upto 50 V. The resistance to be connected in series with the galvanometer (in ohms) is

• 2010

• 4050

• 5040

• 4960

A rectangular coil of 300 turns has an average area of 25 cm x 10 cm . The coil rotates with a speed of 50 cps in uniform magnetic field of strength 4 × 10^-2 T about an axis perpendicular to the field. The peak value of the induced emf is (in volt)

• $300 \mathrm{\pi }$

• $3000 \mathrm{\pi }$

• $3 \mathrm{\pi }$

• $30 \mathrm{\pi }$

A vertical circular coil ofradius 0.1 m and having 10 turns carries a steady current. When the plane of the coil is normal to the magnetic meridian, a neutral point is observed at the centre of the coil. If B_H = 0314 × 10^-4 T, the current in the coil is

• 0.5 A

• 0.25 A

• 2 A

• 1 A