Why does a coil rotate when placed in a magnetic field with current flowing?

A coil rotates in a magnetic field with current flowing due to the interaction between the magnetic field and the current, creating a torque.

When a current-carrying coil is placed in a magnetic field, it experiences a force. This force is a result of the interaction between the magnetic field and the current flowing through the coil. According to Fleming's Left Hand Rule, the force acts perpendicular to both the direction of the current and the magnetic field. This force causes the coil to rotate, a principle that is fundamental to the operation of electric motors.

To understand the basics of magnetic fields and their interaction with electric current, Magnetic Field Basics provides foundational knowledge. Similarly, the Magnetic Field Due to Current page explores how electric currents create magnetic fields which are essential to this process.

The magnitude of the force experienced by the coil is given by the equation F = BILsinθ, where F is the force, B is the magnetic field strength, I is the current, L is the length of the wire, and θ is the angle between the direction of the current and the magnetic field. The direction of the force is given by Fleming's Left Hand Rule. If the coil is free to rotate, this force will cause it to do so.

The force on each side of the coil creates a torque, which causes the coil to rotate. The torque τ is given by the equation τ = Fd, where F is the force and d is the distance from the pivot point to the line of action of the force. As the coil rotates, the direction of the current changes, which changes the direction of the force and keeps the coil rotating. This change in force direction maintains the coil's rotation, much like the principles discussed in the Basics of Simple Harmonic Motion (SHM), though the contexts differ.

The rotation of the coil in a magnetic field is the basis for the operation of many electrical devices, including electric motors and generators. In an electric motor, a current is passed through a coil in a magnetic field, causing the coil to rotate and drive a shaft. In a generator, the process is reversed: a coil is rotated in a magnetic field, inducing a current in the coil.

Understanding the laws of motion, such as Newton's First Law, is crucial in comprehending how forces act on objects, including in scenarios involving magnetic fields and electric currents.

In conclusion, the rotation of a coil in a magnetic field with current flowing is due to the interaction between the magnetic field and the current, which creates a force and a torque that cause the coil to rotate. This principle is fundamental to the operation of many electrical devices.