7. The frequency of torsional oscillation of a thin cylindrical magnet suspended

Question

7. The frequency of torsional oscillation of a thin cylindrical magnet suspended between Helmholtz coils aligned to the earth's magnetic field is directly proportional to the: (a) the moment of inertia of the magnet perpendicular to it's length. (b) square of the magnet's dipole moment. (C) square root of the magnet's dipole moment (d) square of the current density per unit length (e) square root of the current density per unit length 8. Draw a circle in the space below; this represents a loop of copper wire. Imagine that the tip of your pencil is the north pole of a bar magnet. Start with tip in the center of the circle. As you lift the tip off the paper, what is the direction of the induced current in the conducting loop? (a) Clockwise (b) Counterclockwise (c) There will be no induced 9. Three identical lamps are connected in series as shown. When the switch is closed Ó Ó 30V S/ (a) lamps 1 and 2 turn off; lamp 3 gets brighter (b) lamps 1 and 2 turn off; lamp 3 gets dimmer (c) lamps 1 and 2 get brighter; lamp 3 turns off (d) lamps 1 and 2 get dimmer; lamp 3 turns off (e) all the lamps get brighter Page 3 of 11

Explanation / Answer

Q)8 As the magnet is going away flux through the wire is decreasing thus it will try to retain the flux by inducing current in clockwise direction which will increse magnetic flux goping inside the page . therefore clockwise.

Q9) Lamp 3 will get short circuited thus no current will flow through lamp 3 and it will turn off. Net resistance will decrease thus current will increase through A and B thus incresaing their brightness. Lamp a and B will get brighter.

option C is correct

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