Directions : In the following question more than one of the answers given may be correct. Select the correct answer and mark it according to the code:
A charged particle enters into a region which offers a resistance against its motion and uniform magnetic field exists in the region. The particle traces a spiral path as shown in the figure. Which of the following statements is/are correct?
(1) Component of the magnetic field in the plane of spiral is zero (2) Particle enters from region at Q (3) If the magnetic field is outward then the particle is positively charged (4) Since force exerted by magnetic field is always normal to the direction of motion, therefore, its angular momentum remains unchanged
A) 1, 2 and 3 are correct
B) 1 and 2 are correct
C) 2 and 4 are correct
D) 1 and 3 are correct
Correct Answer: A
Solution :
As the force exerted by the magnetic field is always towards the centre of the path traced and in the plane of the path, hence the magnetic field should be always normal to the plane. The particle is continuously losing its energy. Hence radius of the path will decrease. Hence particle will enter from Q. From right palm rule we can verify that (3) is correct. As the particle always experiences a resisting force. Torque due to resisting force is not zero. Hence, angular momentum is not constant.
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