A charged particle enters a region of uniform magnetic field B with different orientations of its velocity vector v with respect to B. Answer the following with suitable reasoning.
a. (i) Explain why the particle travels in a straight line when the angle θ between v and B is 0∘ or 180∘. State the nature of the force acting in this case.
b. (ii) Describe the trajectory when θ is exactly 90∘. Why is the path of this special shape?
c. (iii) For 0∘<θ<90∘, name and describe the resulting path. Show with words (no diagram required) how the right-hand rule helps to decide the sense (clockwise or anticlockwise) of rotation for (a) a positive charge and (b) a negative charge.