InterviewSolution

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1.	A magnetic field that varies in magnitude from point to point but has a constant direction (east to west) is set up in a chamber. A charged particle enters the chamber and travels undeflected along a straight path with constant speed. What can you say about the initial velocity of the particle?
Answer» The force on a charged particle moving inside the magnetic field is given by \(\vec F_m = q(\vec v \times \vec B)\) The force on the charged particle coil bd zero (will remain undeflected), if v x B is zero. Therefore, either the initial velocity v is parallel or anti-parallel to the magnetic field B.

2.	A current carrying loop is placed in a uniform magnetic field. The torque acting on it does not depend upon(A) Shape of loop(B) Size of loop(C) Value of current(D) Magnetic field
Answer» The answer is (A) Shape of loop

3.	An electron travelling west to east enters a chamber having a uniform electrostatic field in north to south direction. Specify the direction in which a uniform magnetic field should be set up to prevent the electron from deflecting from its straight-line path.
Answer» Under the action of electrostatic field, the electron will be deflected towards north (towards the positive plate). It will remain undeflected if the force due to the magnetic field is towards south. As the velocity: y of the electron is from west to east, the expression for the magnetic Lorentz force i.e. \(\vec F_m = -e(\vec v \times \vec B)\) it tells that the magnetic field \(\vec B\) should be applied along the vertical and in downward direction. The direction of the magnetic field may be found by applying Fleming’s left hand rule.

4.	A long straight wire of radius ‘a’ carries a steady current I. The current is uniformly distributed across its cross-section. The ratio of the magnetic field at a/2 and 2a is(A) \(\frac{1}{4}\)(B) \(\frac{1}{2}\)(C) 1(D) 4
Answer» The answer is (C) 1

5.	A uniform magnetic fields get modified, when two specimen X and Y are placed in it. Identify X and Y.
Answer» X is diamagnetic and Y is ferromagnetic.

6.	What is the angle of dip at the equator and at the pole?
Answer» The angle of dip at the equator is 0° and the angle of dip at the pole is 90°.

7.	An ammeter and a millimeter are converted from the same galvanometer. Out of the two, which current measuring instrument has higher resistance.
Answer» Millimeter has higher resistance as an ammeter requires a shunt and smaller resistance.

8.	Why is an ammeter always connected in series?
Answer» An ammeter is used to read the circuit current. So it has to be put in series in the circuit. Also an ammeter has low resistance. If it is connected in parallel, it may draw heavy current which can damage the instrument.