Title MAGNETISM & MATTER.pdf ✅

CHAPTER 5 MAGNETISM & MATTER Exercise 1: NCERT Based Topic-wise MCQs 5.1 & 5.2 INTRODUCTION & THE BAR MAGNET 1. If a bar magnet of pole strength m and magnetic moment M is cut perpendicular to its axis in two equal halves then its new pole strength m′ and magnetic moment M′ are respectively NCERT Page-177 / N-139 (a) m′ = m and M′ = M (b) m′ = m and M′ = M 2 (c) m′ = m 2 and M′ = 2M (d) m′ = 2m and M′ = M 2 2*. A small bar magnet placed with its axis at 30∘ with an external field of 0.06T experiences a torque of 0.018Nm. The minimum work required to rotate it from its stable to unstable equilibrium position is : (a) 6.4 × 10−2 J NCERT Page-178 / N-139 (b) 9.2 × 10−3 J (c) 7.2 × 10−2 J (d) 11.7 × 10−3 J 3. For bar magnet effective length (Le ) related with geometrical length (Lg) as NCERT Page-177 / N-139 (a) Le = 6 5 Lg (b) Le = 5 6 Lg (c) Le = Lg (d) Le = 2Lg 4. A bar magnet is cut into two equal halves by a plane parallel to the magnetic axis. Of the following physical quantities the one which remains unchanged is NCERT Page-177 / N-139 (a) pole strength (b) magnetic moment (c) intensity of magnetization (d) None of these 5. A steel wire of length l has a magnetic moment M. It is bent in L-shape (Figure). The new magnetic moment is NCERT Page-177 / N-139 (a) M (b) M √2 (c) M 2 (d) 2M 6. Magnetic dipole moment is a vector quantity directed from NCERT Page-177 / N-139
(a) south pole to north pole (b) north pole to south pole (c) east to west (d) west to east 7. A thin bar magnet of length 2l and breadth 2 b pole strength m and magnetic moment M is divided into four equal parts with length and breadth of each part being half of original magnet. Then the pole strength of each part is (a) m NCERT Page-177 / N-139 (b) m/2 (c) 2m (d) m/4 8. The force between magnetic poles when their pole strength and the distance between them both doubled is (a) twice the previous value (b) half the previous value (c) four times the previous value (d) not change 9. A coil in the shape of an equilateral triangle of side 10cm lies in a vertical plane between the pole pieces of permanent magnet producing a horizontal magnetic field 20mT. The torque acting on the coil when a current of 0.2 A is passed through it and its plane becomes parallel to the magnetic field will be √x × 10−5Nm. The value of x is (a) 3 NCERT Page-178 / N-139 (b) 5 (c) 7 (d) 9 10. A bar magnet of magnetic moment M, is placed in magnetic field of induction B. The torque exerted on it is (a) M⃗ B⃗ NCERT Page-178 / N-139 (b) −M⃗ ⋅ B⃗ (c) M⃗ × B⃗ (d) −B⃗ × M⃗ 11. The magnetic moment of a bar magnet is thus ...A... to the magnetic moment of an equivalent solenoid that produces the same magnetic field. Here, A refers to NCERT Page-177 / N- 139 (a) unequal (b) different (c) equal (d) same 12. The pole strength of the magnet does not depend on NCERT Page-177 / N-139 (a) area of cross-section (c) length of the magnet (b) nature of material (d) both (a) and (b) 13. A magnetic needle suspended parallel to a magnetic field requires √3J of work to turn it through 60∘ . The torque needed to maintain the needle in this position will be: NCERT Page-178 / N- 139 (a) 2√3J
(b) 3J (c) √3J (d) 3 2 J 14. Magnetic lines of force due to a bar magnet do not intersect because NCERT Page-175 / N-138 (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 force (d) None of these 15. The magnetic lines of force inside a bar magnet NCERT Page-175 / N-138 (a) are from N-pole to S-pole of magnet (b) do not exist (c). depend upon the area of cross section of bar magnet (d) are from S-pole of magnet 16. A circular loop carrying a current is replaced by an equivalent magnetic dipole. A point on the axis of the loop is in (a) end-on position NCERT Page-177 / N-139 (c) both (b) broadside-on position (d) None of these 17. A bar magnet has a length 8cm. The magnetic field at a point at a distance 3cm from the centre in the broad sideon position is found to be 4 × 10−6T. The pole strength of the magnet is. NCERT Page-177 / N-139 (a) 6 × 10−5Am (b) 5 × 10−5Am (c) 2 × 10−4Am (d) 3 × 10−4Am 18*. The work done in turning a magnet of magnetic moment M by an angle of 90∘ from the meridian, is n times the corresponding work done to turn it through an angle of 60∘ . The value of n is given by NCERT Page-176/N-139 (a) 2 (b) 1 (c) 0.5 (d) ⋅ 0.25 19. The ratio of magnetic fields due to a smaller bar magnet in the end on position to broad side on position is (a) 1/4 NCERT Page-177 / N-139 (b) 1/2 (c) 1 (d) 2 20. Let r be the distance of a point on the axis of a bar magnet from its centre. The magentic field at such a point is proportional to NCERT Page-177 / N-139 (a) 1 r (b) 1 r 2
(c) 1 r 3 (d) None of these 21 *A short bar magnet of magnetic moment 0.4JT −1 is placed in a uniform magnetic field of 0.16T. The magnet is in stable equilibrium when the potential energy is NCERT/ Page-178 / N-139 (a) 0.064 (b) zero (c) −0.082J (d) 0.064J 22. The magnetic moment of a magnet is 0.1amp × m2 . It is suspended in a magnetic field of intensity 3 × 10−4 weber/ m2 . The couple acting upon it when deflected by 30∘ from the magnetic field is NCERT/ Page-177 / N-139 (a) 1 × 10−5Nm (b) 1.5 × 10−5Nm (c) 2 × 10−5Nm (d) 2.5 × 10−5Nm 23*. A magnet of magnetic moment 20 C.G.S. units is freely suspended in a uniform magnetic field of intensity 0.3 C.G.S. units. The amount of work done in deflecting it by an angle of 30∘ in C.G.S. units is (a) 6 NCERT Page-178 / N-139 (b) 3√3 (c) 3(2 − √3) (d) 3 24. A magnet of length 0.1m and pole strength 10−4 A.m. is kept in a magnetic field of 30Wb/m2 at an angle 30∘ . The couple acting on it is × 10−4Nm. NCERT Page-177/ N-139 (a) 7.5 (b) 3.0 (c) 1.5 (d) 6.0 25. The magnetic dipole moment of a coil is 5.4 × 10−6 joule/ tesla and it is lined up with an external magnetic field whose strength is 0.80T. Then the work done in rotating the coil (for = 180∘ ) isNCERT Page-178/ N-139 (a) 4.32μJ (b) 2.16μJ (c) 8.6μJ (d) None of these. 25. A bar magnet having a magnetic moment of 2.0 × 105 JT−1 , is placed along the direction of uniform magnetic field of magnitude B = 14 × 10−5T. The work done in rotating the magnet slowly through 60∘ from the direction of field is : NCERT Page-177 / N-139 (a) 14J (b) 8.4J (c) 4J (d) 1.4J 26. A short bar magnet, placed with its axis at 30∘ with an external magnetic field of 0.16T, experiences a torque of magnitude 0.032J. The magnetic moment of the bar magnet is (in units of J/T ) NCERT/ Page-178 / N-139