Moving charges and magnetism

In a certain region of space, electric field

E and magnetic field

B are perpendicular to each other. An electron enters perpendicularly to both the fields and moves undeflected. The velocity of electron is

• E/B

• B/E

• E x B

• E.B

A deuteron of kinetic energy 50 keV is describing a circular orbits of radius 0.5 m in a plane perpendicular to the magnetic field B. The kinetic energy of the proton that describes a circular orbit of same radius and inside same B is

• 25 keV

• 50 keV

• 200 keV

• 100 keV

A rectangular coil ABCD is placed near a long straight current carrying straight wire as shown. What is the net force on the rectangular coil?

• 25 x 10-7 N towards the wire

• 25 x 10-7 N away from the wire

• 35 x 10-7 N, towards the wire

• 35 x 10-7 N, away from the wire

To convert a moving coil galvanometer into on ammeter of given range, we must connect:

• A suitable low resistance in series

• A suitable low resistance in parallel

• A suitable high resistance in parallel

• A suitable high resistance in series

Two wires of same length are shaped into a square and a circle if they carry same current, ratio of magnetic moment is :

• 2 : pi

• pi: 2

• pi: 4

• 4:pi

Current sensitivity of a galvanometer can be increased by decreasing :

• Magnetic field B

• number of turns N

• torsional constant K

• Area A

An electric current passes through a long straight copper wire. At a distance 5 cm from the straight wire, the magnetic field is B. The magnetic field at 20 cm from the straight wire would be

• B/6

• B/4

• B/3

• B/2

A wire in the form of a circular loop, of one turn carrying a current, produces magnetic induction 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

• B

• 2B

• 4B

• 8B

Currents of 10 A and 2 A are flowing in opposite directions through two parallel wires A and B respectively. If the wire A is infinitely long and wire B is 2 m long, then force on wire B which is situated at 10 cm from A, is

• 8 x 10 ^ -5 N

• 6 x 10 ^-5 N

• 4 x 10 ^ -5 N

• 2 X 10 ^ -5 N

A 100 turns coil shown in the figure carries a current of 2 A in a magnetic field of .2Wbm2 The torque acting on the coil is

• 0.32 N-m tending to rotate the side AC into the page

• 0.32 N-m tending to rotate the side AC out of the page

• 0.64 N-m tending to rotate the side AC into the page

• 0.64 N-m tending to rotate the side AC out of the page