A current flows in a conductor from east to west. The direction of the magnetic field at a point above the conductor is

• towards east

• towards west

• towards north

• towards south

A tangent galvanometer has a reduction factor of 1 A and it is placed with the plane of its coil perpendicular to the magnetic meridian. The deflection produced when a current of 1 A is passed through it is

• 60°

• 45°

• 30°

• None of these

An electric field of 1500 V/m and a magnetic field of 0.40 weber/metre² act on a moving electron. The minimum uniform speed along a straight line the electron could have is

• 1.6 × 10¹⁵ m/s

• 6 × 10^-16 m/s

• 3.75 × 10³ m/s

• 3.75 × 10² m/s

In an ammeter 10% of main current is passing through the galvanometer. If the resistance of the galvanometer is G, then the shunt resistance, in ohms is

• 9G

• $\frac{\mathrm{G}}{9}$

• 90G

• $\frac{\mathrm{G}}{90}$

Electron of mass m and charge q is travelling with a speed v along a circular path of radius r at right angles to a uniform magnetic field of intensity B. If the speed of the electron is doubled and the magnetic field is halved the resulting path would have a radius

• 2r

• 4r

• r/4

• r/2

A galvanometer coil has a resistance of 15 Ω and gives full scale deflection for a current of 4 mA. To convertit to an ammeter of range 0 to 6 A

• 10 m Ω resistance is to be connected in parallel to the galvanometer

• 10 m Ω resistance is to be connected in series with the galvanometer

• 0.1 Ω resistance is to be connected in parallel to the galvanometer

• 0.1 Ω resistance is to be connected in series with the galvanometer

A straight wire of mass 200 g and length 1.5 m carries a current of 2 A. It is suspended in mid-air by a uniform horizontal magnetic field B. The magnitude of B (in tesla) is (assume g = 9.8 ms^-2)

• 2

• 1.5

• 0.55

• 0.65

A solenoid 1.5 m long and 0.4 cm in diameter possesses 10 turns per cm length. A current of 5 A falls through it. The magnetic field at the axis inside the solenoid is

• $2\mathrm{\pi } \times {10}^{-3} \mathrm{T}$

• $2\mathrm{\pi } \times {10}^{-5} \mathrm{T}$

• $4\mathrm{\pi } \times {10}^{-2} \mathrm{T}$

• $4\mathrm{\pi } \times {10}^{-3} \mathrm{T}$

109.

A wire PQR is bent as shown in figure and is placed in a region of uniform magnetic field B. The length of PQ = QR = l. A current I ampere flows through the wire as shown. The magnitude of the force on PQ and QR will be

          

• BIl, 0

• 2 BIl, 0

• 0, BIl

• 0,0

A circular coil carrying a certain current produces a magnetic field B₀ at its centre. The coil is now rewound so as to have 3 turns and the same current is passed through it. The new magnetic field at the centre is

• $\frac{{\mathrm{B}}_0}{9}$

• 9B₀

• $\frac{{\mathrm{B}}_0}{3}$

• 3B₀