 # Moving Charges and Magnetism

## The force existing between two magnets, due to interaction of their magnetic fields is called magnetic force. Magnetic force results in the attraction and repulsion between the two magnets. The current or moving charges produce a magnetic field. Principle of superposition states 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. Magnetic field is the space surrounding a magnet, in which its magnetic force is felt by any other magnetic material. The motion of a charged particle in uniform magnetic field is circular in nature. The nature of motion is helical when the charged particle is projected at an angle with the magnetic field. A device called cyclotron applies the concept of circular motion of charged particle to accelerate the positively charged particles like protons; deuterons, etc. Biot – Savart’s law describes the magnetic field due to a current carrying element and magnetic field on the axis of a circular current loop. The direction of magnetic field generated on the axis of the circular current loop is given by right hand thumb rule. Ampere’s circuital law is used to find magnetic field due to a solenoid and a toroid. A solenoid consists of an insulating wire closely wound in the form of a helix. The length of the solenoid 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. When two parallel current carrying conductors are placed near each other, they exert a force on each other. If two straight parallel and infinitely long conductors are carrying currents 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) when placed in a magnetic field experiences a torque and is termed as magnetic dipole. Moving coil galvanometer is an instrument which uses the concept of magnetic dipole for detection and measurement of small electric currents.

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