Magnetism and magnetic effects of electric current Book Back Questions & Answers
Unit 3 > Physics > Class 12 > Samacheer Kalvi - English Medium
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1. A circular coil of radius 5 cm and 50 turns carries a current of 3 ampere. The magnetic dipole moment of the coil is nearly
(a) 1.0 amp m2
(b) 1.2 amp m2
(c) 0.5 amp m2
(d) 0.8 amp m2
Correct answer: (b) 1.2 amp m2
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2. A thin insulated wire forms a plane spiral of N = 100 tight turns carrying a current I = 8 m A (milli ampere). The radii of inside and outside turns are a = 50 mm and b = 100 mm respectively. The magnetic induction at the centre of the spiral is
(a) 5 T
(b) 7 T
(c) 8 T
(d) 10 T
Correct answer: (b) 7 T
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3. Three wires of equal lengths are bent in the form of loops. One of the loops is circle, another is a semi-circle and the third one is a square. They are placed in a uniform magnetic field and same electric current is passed through them. Which of the following loop configuration will experience greater torque ?
(a) circle
(b) semi-circle
(c) square
(d) all of them
Correct answer: (a) circle
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4. A bar magnet of length l and magnetic moment pm is bent in the form of an arc as shown in figure. The new magnetic dipole moment will be
(a) pm
(b) 3/ pm
(c) 2/ pm
(d) 1/ 2 pm
Correct answer: (b) 3/ pm
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5. A non-conducting charged ring carrying a charge of q, mass m and radius r is rotated about its axis with constant angular speed . Find the ratio of its magnetic moment with angular momentum is
(a) q/ m
(b) 2q/ m
(c) q/ 2m
(d) q/ 4m
Correct answer: (c) q/ 2m
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6. The BH curve for a ferromagnetic material is shown in the figure. The material is placed inside a long solenoid which contains 1000 turns/cm. The current that should be passed in the solenonid to demagnetize the ferromagnet completely is
(a) 1.00 m A(milli ampere)
(b) 1.25 mA
(c) 1.50 mA
(d) 1.75 mA
Correct answer: (b) 1.25 mA
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7. Two short bar magnets have magnetic moments 1.20 Am2 and 1.00 Am2 respectively. They are kept on a horizontal table parallel to each other with their north poles pointing towards south. They have a common magnetic equator and are separated by a distance of 20.0 cm. The value of the resultant horizontal magnetic induction at the mid-point O of the line joining their centres is (Horizontal components of Earths magnetic induction is 3.6 105 Wb m2 )
(a) 3.60 x 10-5 Wb m-1
(b) 3.5 x 10-5 Wb m-1
(c) 2.56 x 10-4 Wb m-1
(d) 2.2 x 10-4 Wb m-1
Correct answer: (c) 2.56 x 10-4 Wb m-1
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8. The vertical component of Earths magnetic field at a place is equal to the horizontal component. What is the value of angle of dip at this place?
(a) 30
(b) 45
(c) 60
(d) 90
Correct answer: (b) 45
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9. A flat dielectric disc of radius R carries an excess charge on its surface. The surface charge density is . The disc rotates about an axis perpendicular to its plane passing through the centre with angular velocity . Find the magnitude of the torque on the disc if it is placed in a uniform magnetic field whose strength is B which is directed perpendicular to the axis of rotation
(a) 1/4 BR
(b) 1/4 BR2
(c) 1/4 BR3
(d) \1/4 BR4
Correct answer:
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10. The potential energy of magnetic dipole whose dipole moment is p i j m = ( . 0 5 +0 4. ) 2 Am kept in uniform magnetic field B i = 0 2. T
(a) 0.1 J
(b) 0.8 J
(c) 0.1 J
(d) 0.8 J
Correct answer: (c) 0.1 J