CBSE Class 10 Science 2022 · Paper 31/2/3 · Question 14
A student was asked to perform an experiment to study the force on a current carrying conductor in a magnetic field. He took a small aluminum rod AB, a strong horse shoe magnet, some connecting wires, a battery and a switch and connected them as shown. He observed that on passing current, the rod gets displaced. On reversing the direction of current, the direction of displacement also gets reversed. On the basis of your understanding of this phenomenon, answer the following questions :
- (a)State the condition under which the displacement of the rod is largest for the same magnitude of current flowing through it.
- (b)State the rule that determines the direction of the force on the conductor AB.
- (c)(i)(i) If the U shaped magnet is held vertically and the aluminum rod is suspended horizontally with its end B towards due north, then on passing current through the rod from B to A as shown, in which direction will the rod be displaced ? (ii) Name any two devices that use current carrying conductors and magnetic field.
- (c)(ii)OR : Draw the pattern of magnetic field lines produced around a current carrying straight conductor held vertically on a horizontal cardboard. Indicate the direction of the field lines as well as the direction of current flowing through the conductor.
Answer
(a) The displacement is largest when the rod, that is the direction of the current, is at right angles to the direction of the magnetic field.
(b) Fleming's left-hand rule: 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, the thumb points in the direction of the force on (motion of) the conductor AB.
(c)(i) (i) The field is vertically upward (N pole below the rod, S pole above) and the current flows from north to south, so by Fleming's left-hand rule the rod is displaced towards the west. (ii) Electric motor and loudspeaker (the electric generator, the microphone and the galvanometer are other examples).
OR
(c)(ii) The field lines are concentric circles on the cardboard, centred on the wire and closer together near it; for a current flowing upward they run anticlockwise as seen from above (right-hand thumb rule), and clockwise if the current flows downward (see the figure).
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