Engineering Entrance Sample Papers

Magnets and Its Properties Practice Questions

Magnets and Its Properties

Magnet and It’s Properties (Magnetism) JEE Questions:

Ques: The magnetic potential at a point on the axial line of a bar magnet of dipole moment M is V. What is the magnetic potential due to a bar magnet of dipole moment M/4 at the same point
(a) 4V
(b) 2V
(c) V/2
(d) V/4
Ans. (d)

Ques: Two lines of force due to a bar magnet
(a) Intersect at the neutral point
(b) Intersect near the poles of the magnet
(c) Intersect on the equatorial axis of the magnet
(d) Do not intersect at all
Ans. (d)

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Ques: A magnet of magnetic moment 2 JT–1 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
(a) 0.1  J
(b) 0.2 J
(c) 1 J
(d) 2 J
Ans. (b)

Ques: There is no couple acting when two bar magnets are placed coaxially separated by a distance because
(a) There are no forces on the poles
(b) The forces are parallel and their lines of action do not coincide
(c) The forces are perpendicular to each other
(d) The forces act along the same line
Ans. (d)

Ques: Magnetic dipole moment is a
(a) Scalar quantity
(b) Vector quantity
(c) Constant quantity
(d) None of these
Ans. (b)

Ques: A bar magnet of magnetic moment 200 Am2 is suspended in a magnetic field of intensity 0.25 N/A-m. The couple required to deflect it through 30o is
(a) 50 Nm
(b) 25 Nm
(c) 20 Nm
(d) 15 Nm
Ans. (b)

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Ques: If a magnet is hanged with its magnetic axis then it stops in
(a) Magnetic meridian
(b) Geometric meridian
(c) Angle of dip
(d) None of these
Ans. (a)

Ques: The magnetic lines of force inside a bar magnet
(a) Are from south-pole to north-pole of the magnet
(b) Are from north-pole to south-pole of the magnet
(c) Do not exist
(d) Depend upon the area of cross-section of the bar magnet
Ans. (a)

Ques: Two like magnetic poles of strength 10 and 40 SI units are separated by a distance 30 cm. The intensity of magnetic field is zero on the line joining them
(a) At a point 10 cm from the stronger pole
(b) At a point 20 cm from the stronger pole
(c) At the mid-point
(d) At infinity
Ans. (b)

Ques: The incorrect statement regarding the lines of force of the magnetic field B is
(a) Magnetic intensity is a measure of lines of force passing through unit area held normal to it
(b) Magnetic lines of force form a close curve
(c) Inside a magnet, its magnetic lines of force move from north pole of a magnet towards its south pole
(d) Due to a magnet magnetic lines of force never cut each other
Ans. (c)

Ques: The magnetism of magnet is due to
(a) The spin motion of electron
(b) Earth
(c) Pressure of big magnet inside the earth
(d) Cosmic rays
Ans. (a)

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Ques: The direction of line of magnetic field of bar magnet is
(a) From south pole to north pole
(b) From north pole to south pole
(c) Across the bar magnet
(d) From south pole to north pole inside the magnet and from north pole to south pole outside the magnet
Ans. (d)

Ques: A long magnet is cut in two parts in such a way that the ratio of their lengths is 2 : 1. The ratio of pole strengths of both the section is
(a) Equal
(b) In the ratio of 2 : 1
(c) In the ratio of 1 : 2
(d) In the ratio of 4 : 1
Ans. (a)

Ques: Points A and B are situated perpendicular to the axis of a 2cm long bar magnet at large distances X and 3X from its centre on opposite sides. The ratio of the magnetic fields at A and B will be approximately equal to
(a) 1 : 9
(b) 2 : 9
(c) 27 : 1
(d) 9 : 1
Ans. (c)

Ques: Magnetic lines of force due to a bar magnet do not intersect because
(a) A point always has a single net magnetic field
(b) The lines have similar charges and so repel each other
(c) The lines always diverge from a single point
(d) The lines need magnetic lenses to be made to intersect
Ans. (a)

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Ques: A magnetic needle is kept in a non-uniform magnetic field. It experiences
(a) A force and a torque
(b) A force but not a torque
(c) A torque but not a force
(d) Neither a torque nor a force
Ans. (a)

Ques: What happens to the force between magnetic poles when their pole strength and the distance between them are both doubled
(a) Force increases to two times the previous value
(b) No change
(c) Force decreases to half the previous value
(d) Force increases to four times the previous value
Ans. (b)

Ques: If a hole is made at the centre of a bar magnet, then its magnetic moment will
(a) Increase
(b) Decrease
(c) Not change
(d) None of these
Ans. (c)

Ques: The magnet can be completely demagnetized by
(a) Breaking the magnet into small pieces
(b) Heating it slightly
(c) Droping it into ice cold water
(d) A reverse field of appropriate strength
Ans. (d)

Ques: The magnetic field due to a short magnet at a point on its axis at distance X cm from the middle point of the magnet is 200 Gauss. The magnetic field at a point on the neutral axis at a distance X cm from the middle of the magnet is
(a) 100 Gauss
(b) 400 Gauss
(c) 50 Gauss
(d) 200 Gauss
Ans. (a)

Ques: A sensitive magnetic instrument can be shielded very effectively from outside magnetic fields by placing it inside a box of
(a) Teak wood
(b) Plastic material
(c) Soft iron of high permeability
(d) A metal of high conductivity
Ans. (c)

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Vishal Arora

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