(a) (i) A straight cylindrical conductor is suspended with its axis perpendicular to the magnetic field of a horse-shoe magnet. The conductor gets displaced towards left when a current is passed through it. What will happen to the displacement of the conductor if the (1) current through it is increased? (2) horse-shoe magnet is replaced by another stronger horse-shoe magnet? (3) direction of current through it is reversed? (ii) Name and state the rule for determining the direction of force on a current carrying conductor in a magnetic field. OR (b) Draw the pattern of the magnetic field produced around a vertical current carrying straight conductor passing through a horizontal cardboard. Mark the direction of current and the magnetic field lines. Name and state the rule which is used to determine the direction of magnetic field associated with a current carrying conductor.

Option (a)

#### (i) Effects on the displacement of the conductor:

1. If the current through it is increased: The displacement of the conductor will increase (it will deflect more to the left). This is because the magnetic force ($F$) acting on a current-carrying conductor is directly proportional to the current ($I$) flowing through it ($F \propto I$).
2. If the horse-shoe magnet is replaced by a stronger horse-shoe magnet: The displacement of the conductor will increase. A stronger magnet provides a stronger magnetic field ($B$), which increases the magnetic force acting on the conductor ($F \propto B$).
3. If the direction of current through it is reversed: The direction of displacement of the conductor will be reversed (it will get displaced towards the right instead of the left).

#### (ii) Rule for determining the direction of force:

• Name of the Rule: Fleming's Left-Hand Rule.
• Statement: Stretch the thumb, forefinger, and middle finger of your left hand such that they are mutually perpendicular to each other. If the first finger (forefinger) points in the direction of the magnetic field and the second finger (middle finger) points in the direction of the current, then the thumb will point in the direction of motion or the force acting on the conductor.

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OR

Option (b)

#### Pattern of Magnetic Field Lines:

The magnetic field lines around a straight current-carrying conductor form concentric circles centered on the wire.

• Direction of Current: Vertically upwards.
• Direction of Magnetic Field Lines: Anti-clockwise (when viewed from above), as indicated by the arrows on the concentric circles.

#### Rule for determining the direction of magnetic field:

• Name of the Rule: Right-Hand Thumb Rule (or Maxwell's Corkscrew Rule).
• Statement: Imagine that you are holding a current-carrying straight conductor in your right hand such that the thumb points towards the direction of current. Then your fingers will wrap around the conductor in the direction of the field lines of the magnetic field.