Fleming's Left Hand Rule - UNSOLVED PRACTICE SET

Q7. State Fleming's Left Hand Rule. Clearly describe which finger represents which quantity.

Q8. A current-carrying conductor is placed in a magnetic field pointing from North to South. The current flows from East to West. Using Fleming's Left Hand Rule, determine the direction of the force on the conductor.

Q9. Why must the three quantities — Field, Current, and Force — in Fleming's Left Hand Rule always be mutually perpendicular to each other?

Q10. If the current direction in a conductor is reversed (field unchanged), how does the direction of force (as given by Fleming's Left Hand Rule) change? Explain by re-orienting your fingers.

Q11. Distinguish between Fleming's Left Hand Rule and Fleming's Right Hand Rule in terms of:
(a) which device/phenomenon each is used for, and
(b) the general nature of what each rule predicts (cause vs effect).

Q12. A student always gets confused between the left-hand and right-hand rules. Give a simple memory tip connecting 'Left hand → Motor' and explain briefly why this connection makes sense (motors convert electrical energy to motion).

Q13. Explain Fleming's Left Hand Rule in complete detail. Your answer must cover:
(a) the precise statement of the rule (positioning of thumb, first finger, middle finger),
(b) what each finger represents (Force, Field, Current),
(c) a worked example: given the field direction (say, vertically upward) and current direction (say, horizontally toward you), determine the force direction step-by-step,
(d) why this rule only works when field, current, and force are mutually perpendicular, and
(e) the practical importance of this rule in designing electric motors.

Q14. A rectangular current-carrying loop (coil) is placed inside a magnetic field, as in a simple electric motor.
(a) The magnetic field points from the North pole to the South pole (left to right, say). The current in the top arm of the coil flows away from you (into the page). Using Fleming's Left Hand Rule, determine the direction of force on the top arm.
(b) The current in the bottom arm of the coil flows toward you (out of the page) — what is the force direction on the bottom arm?
(c) Compare the forces on the top and bottom arms — are they in the same direction or opposite directions?
(d) What effect does this combination of forces have on the coil — does it push the coil sideways, or does it rotate the coil? Explain.

Q15. Apply Fleming's Left Hand Rule to analyse the following real-life scenario: A loudspeaker contains a coil of wire (the voice coil) placed in the magnetic field of a permanent magnet. When an audio signal (alternating current) passes through the coil, the coil moves back and forth, vibrating a diaphragm to produce sound.
(a) Explain, using Fleming's Left Hand Rule, why the coil experiences a force when current flows through it in the magnetic field.
(b) Why does the coil move in one direction when current flows one way, and in the opposite direction when current reverses?
(c) How does this rapid back-and-forth motion (due to AC audio signal) create sound waves?
(d) Why is a strong permanent magnet (often described in speaker specifications) important for loud, clear sound?

Q16. A horizontal current-carrying wire runs from West to East. It is placed in a magnetic field pointing vertically downward (from above the wire to below it).
(a) Using Fleming's Left Hand Rule, determine the direction of the force on the wire (North, South, up, or down).
(b) If the current direction is reversed (East to West), what is the new force direction?
(c) If both the current AND field directions are reversed from the original, what is the force direction now — same as (a) or different? Explain.

Q17. In a DC motor, a rectangular coil ABCD is placed in a magnetic field such that side AB carries current into the page and side CD carries current out of the page (the field points from left — North pole — to right — South pole).
(a) Using Fleming's Left Hand Rule, find the direction of force on side AB.
(b) Find the direction of force on side CD.
(c) Explain how these two forces (in opposite directions on opposite sides) cause the coil to rotate rather than move linearly.
(d) After the coil rotates 180°, the split-ring commutator reverses the current direction in AB and CD. Why is this reversal necessary for continuous rotation?

Q18. A straight conducting rod lies on a horizontal table between the poles of a U-shaped magnet (field pointing from North pole to South pole, horizontally). A battery is connected so current flows through the rod from one rail to the other.
(a) Using Fleming's Left Hand Rule, determine whether the rod will move toward the open end of the U-magnet or toward the closed end (the back).
(b) If the battery's terminals are swapped (reversing current direction), how does the rod's motion change?
(c) If the U-magnet is replaced with one of opposite polarity (poles swapped), how does the rod's motion change compared to the original?
(d) Predict what would happen if the rod were placed parallel to the magnetic field lines instead of perpendicular.