CBSE Class 10 Science 2019 · Paper 31/1/1/C · Question 21

(a) The tangent to a field line at any point gives the direction of the magnetic field at that point. If two field lines intersected, there would be two tangents, and hence two directions of the magnetic field, at the point of intersection - a compass needle placed there would point in two directions at once, which is not possible. So two field lines never intersect. (b) Inside a current-carrying solenoid the field lines are parallel straight lines, equally spaced. So the field has the same strength (magnitude) and the same direction at all points inside: it is uniform. (c) Stretch the thumb, forefinger and middle finger of the left hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of the current, then the thumb gives the direction of the force on (motion of) the conductor. (d) Any two of: (i) an electromagnet in place of a permanent magnet; (ii) a large number of turns of conducting wire in the coil; (iii) the coil wound on a soft iron core (armature).