Question

State the two ways to increase the force on a current-carrying conductor in a magnetic field. Name one device whose working depends on this effect. State Fleming’s left-hand rule with the help of a labelled diagram.

Hint:

To increase magnetic force: increase \( B \) or \( I \). - Fleming’s Left-Hand Rule helps determine the direction of force in devices like electric motors.

Answer 1

Step 1: Two ways to increase the force on a current-carrying conductor:

• (i)
  Increase the strength of the magnetic field (B) — A stronger field exerts a larger force on the conductor.
• (ii)
  Increase the magnitude of current (I) flowing through the conductor — Force is directly proportional to current.

\[ F = BIL \sin\theta \]
where:
\( F \) = force on the conductor, \( B \) = magnetic field strength, \( I \) = current, \( L \) = length of the conductor in the field, \( \theta \) = angle between field and current.

Step 2: Device based on this principle:

The working of an
electric motor depends on the force experienced by a current-carrying conductor in a magnetic field.

Step 3: Fleming’s Left-Hand Rule:

It states that —

“If the forefinger, middle finger, and thumb of the left hand are stretched mutually perpendicular to each other, then —”

• The
  Forefinger points in the direction of the
  magnetic field (B).
• The
  Middle finger points in the direction of the
  current (I).
• The
  Thumb points in the direction of the
  force or motion (F) on the conductor.

Labelled Diagram — Fleming’s Left-Hand Rule

 

Note: The interaction between magnetic field and electric current is the fundamental principle behind all
electromechanical devices such as electric motors, loudspeakers, and galvanometers.