Science — CBSE Class 10 board question

(a) Take a small aluminium rod AB suspended horizontally between the poles of a horse-shoe magnet (N pole below, S pole above), so the magnetic field is directed upward. Connect the rod in series with a battery and key. Pass current from B to A — the rod is displaced towards the left. On reversing the current, it displaces to the right. This shows that a current-carrying conductor in a magnetic field experiences a force.

(b) The electron beam moves from back wall to front wall (away from me). Current is taken opposite to electron motion, so conventional current is directed towards the back wall (towards me). The beam deflects to my right. Applying Fleming's Left-Hand Rule (force → right, current → towards me), the magnetic field is directed vertically downward.

Source: Chapter 12, Section 12.3

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• (a) Describe Activity 12.7 from the textbook — mention the aluminium rod, horse-shoe magnet, direction of current, and observed displacement. Don't just state the concept; narrate the activity steps briefly.
• (b) Key trap: electron motion ≠ conventional current direction (it is opposite). Set up three directions — force (right), current (toward you/back), then use Fleming's Left-Hand Rule to find the field pointing downward. Practice visualising the three mutually perpendicular directions clearly.