Moving Charges and Magnetism - Online Test
Q1. In a coil of 0.1 m radius and 100 turns, 0.1 amp current is passed. What will be the magnetic field at the centre of the coil
Answer : Option C
Explaination / Solution:
Q2. The magnetic field due to a current carrying circular loop of radius 3 cm at a point on the axis at a distance of 4 cm from the centre is 54 μT. what will be its value at the centre of the loop?
Answer : Option D
Explaination / Solution:
The magnetic field at the centre of a coil of radius R and number of turns N , carrying a current I is . At a point distance x from the coil, the field is
Q3. A circular coil of radius R carries an electric current. The magnetic field due to the coil at a point on the axis of the coil located at a distance r from the center of the coil such that r>>R, varies as
Answer : Option B
Explaination / Solution:
At a point distance r from the coil, the magnetic field is . If is neglected in the denominator;
Q4. A long wire carries a steady current. It is bent into a circle of one turn and the magnetic field at the centre of the coil is B. It is then bent into a circular loop of n turns. The magnetic field at the centre of the coil will be
Answer : Option C
Explaination / Solution:
If the length of the wire is L and the radii of the coils in two cases be and . Then,
Q5. In hydrogen atom, the electron is making rev./sec around the nucleus in an orbit of radius 0.528 Å .The magnetic moment () will be
Answer : Option B
Explaination / Solution:
Magnetic moment of the electron .The current due to the orbiting electron
. The magnetic moment
. The magnetic moment
Q6. A magnetic needle lying parallel to a magnetic field requires W units of work to turn it, through 600. The torque needed to maintain the needle in this position will be
Answer : Option B
Explaination / Solution:
the work done to turn a needle through an angle θ is The torque needed to maintain ..
Q7. If number of turns, area and current through a coil is given by n, A and i respectively then its magnetic moment will be
Answer : Option D
Explaination / Solution:
The magnetic moment associated with a coil carrying current is given by the product of its area and the current through it. M=n I A
Q8. The work done in rotating a magnet of magnetic moment in a magnetic field of T form the direction along the magnetic field to opposite direction to the magnetic field, is
Answer : Option A
Explaination / Solution:
The potential energy of a magnetic dipole of moment m placed in a magnetic field is When the magnet is aligned in the direction of the field, and the initial potential energy When the magnet is aligned opposite to the direction of the fieldits potential energy isWork done in rotating the magnet is equal to the change in its potential energy.
Q9. A magnet of magnetic moment is aligned in the direction of magnetic field of 0.1.T. What is the net work done to bring the magnet normal to the magnetic field?
Answer : Option B
Explaination / Solution:
The potential energy of a magnetic dipole of moment m placed in a magnetic field is .When the magnet is aligned in the direction of the field, and the initial potential energy When the magnet is placed perpendicular to the direction of the field,its potential energy is .Work done in rotating the magnet is equal to the change in its potential energy.
Q10. A bar magnet is equivalent to
Answer : Option A
Explaination / Solution:
A solenoid carrying current produces a magnetic field very similar to that of bar magnet. The magnetic field lines emerge from the ends of a solenoid and the number of field lines near its perpendicular bisector is almost equal to zero. A circular coil produces field along its axis. A straight conductor produces a magnetic field that can be represented by concentric circles. A toroid is a solenoid that has collapsed on itself. The field in a toroid is confined to the ring like region bounded by the toroid.
