MAGNETIC EFFECTS OF CURRENT & MAGNETISM HOTS QUESTIONS (SOLVED)

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1 MAGNETIC EFFECTS OF CURRENT & MAGNETISM HOTS QUESTIONS (SOLVED) Q1> A long straight wire AB carries a current of 4 A. A proton p travels at 4* 10 6 ms -1, parallel to the wire, 0.2m from it and in a direction opposite to the current as shown in figure. Calculate the force which the magnetic field of current exerts on the proton. Also, specify the direction of the force. B 4A 0.2m P 4x10 6 ms -1 Ans: the magnetic field at P due to current in wire AB is B= µ o I = 4πx10-7 x4 = 4X10-6 T 2πr 2πx0.2 This field is perpendicular to the direction of motion of the portion and into the plane of the paper i.e. θ=90 o 1 XII Physics

2 Force on the proton F= qvbsinθ =1.6X10-19 X4X10 6 X4X10-6 =2.56X10-18 N Q2. A magnetic needle suspended freely in a uniform magnetic field experiences a torque but no net force. An iron nail near a bar magnet, however experiences a force of attraction in addition to torque, why? Ans: In a uniform magnetic field each pole of a magnet experiences equal and opposite forces, hence the net force on the magnetic needle will be zero. On the other hand an iron nail placed near a bar magnet get magnetized and its poles are in non uniform magnetic field, so the forces experienced by its 2 poles are not equal in magnitude, though they are opposite in direction; so net force on magnetized iron nail is not zero. Q.3 what kind of ferromagnetic material is used for coating magnetic tapes in a cassette player or for building memory stores in a modern computer? Ans: Ceramics are used for coating magnetic tapes in a cassette player or for building stores in a modern computer. Ceramics are specially treated barium iron oxide are also called Ferrites. Q.4. A muon is a particle that has the same charge as an electron but is 200 times heavier than it. If we had an atom in which the muon revolves around a proton instead of an electron, what would be the magnetic moment of the muon in the ground state of such an atom? 2 XII Physics

3 Ans: Magnetic moment of muon in the ground state: \ M l = e L 2m µ where L=h 2π Therefore Ml= 1 X 1.6X10-19 X6.63X X3.14X9.1X10-31 =4.64X10-26 Am 2 Q5> Two long parallel wires are hanging freely. If they are connected to battery (i) in series (ii) in parallels, what would be the effect on their positions? Ans> (i) When the battery is connected in series the current in the two wires will be in opposite directions due to which the force of repulsion will be acting between them and they will move further apart. (ii) When the battery is connected in parallel wires, the current in the two wires will be in the same direction. Due to which the force of attraction will be acting between them and they will come close to each other Q6> The current carrying planar loop suspended in a vertical plane normal to magnetic meridian is in stable equilibrium. The horizontal component of earth s magnetic field is 0.32G.Another horizontal magnetic field of 3 XII Physics

4 magnitude 0.48 g parallel to the plane of the loop is set up along magnetic west to east. Specify the stable equilibrium. Ans> Here, H=0.32 G, F=0.48 G A current loop behaves as a magnetic dipole. The loop is initially along EW normal to magnetic meridian, so that its magnetic moment is along H. Under the combined action of F and H, the loop turns through an angle θ so that its magnetic moment M makes an angle θ with H. According to tangent law, F=H tanθ Tanθ=F/H =0.48/0.32 =1.5 Θ=tan -1 (1.5) = east of north Q7> Two very long straight wires P and Q carry currents of 10A and 20A respectively and are at a distance 20cm apart. If a third wire R (length=15cm) having a current of 10 A is placed in middle between them, how much force will act on R? The direction of current in all the three wires is the same. Ans> Net force on the conductor R towards linear conductor Q will be =F 2 -F 1 4 XII Physics

5 =3.0*10 5 N towards Q 5 XII Physics

6 UNSOLVED (HOTS QUESTIONS) Q1> A current of 10A flows through a semicircular wire of radius 2cm as shown in figure (a). What is direction and magnitude of the magnetic field at the centre of semicircle? Would your answer change if the wire were bent as shown in figure (b)? Q2> Two identical circular loops P and Q carrying equal currents are placed such that their geometrical axis are perpendicular to each other as shown in figure. And the direction of current appear s anticlockwise as seen from point O which is equidistant from loop P and Q. Find the magnitude and direction of the net magnetic field produced at the point O. Q3> In the circuit, the current is to be measured. What is the value of the current if the ammeter shown : (a) is a galvanometer with a resistance R = 60, (b) is a galvanometer described in fig but converted to an ammeter by a shunt resistance r s = 0.02 (c) is an ideal ammeter with zero resistance? 6 XII Physics

7 Q4> How can a moving coil galvanometer be converted into a voltmeter of a given range. Write the Necessary mathematical steps to obtain the value of resistance required for this purpose 7 XII Physics

8 8 XII Physics

MAGNETIC EFFECTS OF CURRENT AND MAGNETISM

UNIT III MAGNETIC EFFECTS OF CURRENT AND MAGNETISM Weightage 8 Marks Concept of magnetic field and Oersted s experiment Biot-savart law and its application to current carrying circular loop. Ampere s law