Force on Current-Carrying Conductor MCQs Quiz | Class 10
This quiz covers Class X Science (Code 086), Unit IV: Effects of Current, focusing on the topic of Force on Current-Carrying Conductor, including the motor effect and direction dependence. Test your knowledge by attempting the questions below and download a PDF of your answers at the end.
Understanding Force on a Current-Carrying Conductor
When a current-carrying conductor is placed in a magnetic field, it experiences a force. This phenomenon is fundamental to the working of electric motors and various other electromagnetic devices. The force arises due to the interaction between the magnetic field produced by the current in the conductor and the external magnetic field.
The Motor Effect
The motor effect is the principle by which a current-carrying conductor in a magnetic field experiences a force. This force is what causes the rotation in an electric motor. The magnitude of this force depends on several factors:
- Current (I): The force is directly proportional to the current flowing through the conductor.
- Magnetic Field Strength (B): The force is directly proportional to the strength of the magnetic field.
- Length of Conductor (L): The force is directly proportional to the length of the conductor exposed to the magnetic field.
- Angle (theta): The force is maximum when the conductor is perpendicular (90 degrees) to the magnetic field lines and zero when it is parallel (0 degrees).
The force can be mathematically expressed as: F = BILsin(theta)
Direction Dependence: Fleming’s Left-Hand Rule
The direction of the force on the conductor is crucial. It is determined by the directions of both the current and the magnetic field. Fleming’s Left-Hand Rule provides a simple way to remember this relationship:
| Finger | Represents |
|---|---|
| Thumb | Direction of Force (Motion) |
| Forefinger | Direction of Magnetic Field |
| Middle Finger | Direction of Current |
To apply the rule, stretch the thumb, forefinger, and middle finger of your left hand mutually perpendicularly to each other. If the forefinger points in the direction of the magnetic field and the middle finger points in the direction of the current, then the thumb will point in the direction of the force on the conductor.
Key Applications and Principles
- Electric Motors: The motor effect is the operating principle behind all electric motors, converting electrical energy into mechanical energy.
- Galvanometers: These devices use the motor effect to detect and measure small electric currents.
- Loudspeakers: The vibration of a coil in a magnetic field due to varying current produces sound.
- Lorentz Force: The force experienced by a charge moving in a magnetic field is called the Lorentz force. The force on a current-carrying conductor is the macroscopic effect of Lorentz forces acting on the individual moving charges (electrons) within the conductor.
Quick Revision Points
- A current-carrying conductor in a magnetic field experiences a force.
- This force is maximum when the conductor is perpendicular to the field.
- Fleming’s Left-Hand Rule determines the direction of force, magnetic field, and current.
- Electric motors work on the principle of the motor effect.
- The direction of force reverses if either the direction of current or magnetic field is reversed.
Practice Questions
- What happens to the force on a current-carrying conductor in a magnetic field if the direction of current is reversed?
- State the rule used to find the direction of force on a current-carrying conductor placed in a magnetic field.
- A conductor is placed parallel to the magnetic field lines. What will be the magnitude of the force experienced by it?
- List two factors on which the magnitude of force on a current-carrying conductor in a magnetic field depends.
- Explain why an electric motor uses a split ring commutator.
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