 # Moving Charges and Magnetism

## Magnetic force is the force existing between two magnets, due to interaction of their magnetic fields. Magnetic force results in the attraction and repulsion between the two magnets. The moving charges produce a magnetic field. Superposition principle says that if there is more than one charge, the fields are added vectorially. Lorentz force is the force experienced by a charge moving under the influence of electric and magnetic field. The space around a magnet, in which its magnetic force is felt by any other magnetic material, is known as Magnetic field. In uniform magnetic field the motion of a charged particle is circular in nature. When the charged particle is projected at an angle with the magnetic field then it moves on helical path. A cyclotron is a device that applies the concept of circular motion of charged particle to accelerate the positively charged particles like protons, deuterons, etc. The magnetic field due to a current carrying element and magnetic field on the axis of a circular current loop is described by Biot – Savart’s law. Right hand thumb rule gives the direction of magnetic field generated on the axis of the circular current loop. Magnetic field due to a solenoid and a toroid is determined by Ampere’s circuital law. A solenoid consists of an insulating wire closely wound in the form of a helix and its length is larger as compared to its radius. A toroid is a hollow circular ring on which a large number of turns of a wire are closely wounded. It is also viewed as a solenoid, which has been bent into a circular shape to close on itself. Two parallel current carrying conductors exert force on each other when they are placed near each other. When current flowing through two straight parallel and infinitely long conductors in the same direction and are separated by a distance r, then there is a force of attraction between them. If the currents are in opposite direction, then there is a force of repulsion. The concept is used to find the torque acting on rectangular current carrying loop. A rectangular loop carrying a steady current (I) experiences a torque when placed in a magnetic field and is termed as magnetic dipole. For detection and measurement of small electric currents, an instrument is used known as Moving coil galvanometer which uses the concept of magnetic dipole.

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