When a charged particle moves through a magnetic field in perpendicular direction, then the charged particle follow a circular path and a magnetic force (F) acts on it which changes the direction of particle but does not alter the magnitude of its velocity (i.e. speed). The force acting on the particle is given by,
\(F = qv \times B\)
Thus, the speed of the particle remains unchanged.
Note: If a charged particle moves at \(45^{\circ}\) to magnetic field then path of the particle will be a helix whose circular part has radius as per the relation
\(r=\frac{m v \sin \theta}{q B}\)
Moving charges generate an electric field and the rate of flow of charge is known as current. This is the basic concept in Electrostatics. Another important concept related to moving electric charges is the magnetic effect of current. Magnetism is caused by the current.
Region in space around a magnet where the Magnet has its Magnetic effect is called the Magnetic field of the Magnet. Let us suppose that there is a point charge q (moving with a velocity v and, located at r at a given time t) in presence of both the electric field E (r) and the magnetic field B (r). The force on an electric charge q due to both of them can be written as,
F = q [ E (r) + v × B (r)] ≡ EElectric +Fmagnetic
This force was based on the extensive experiments of Ampere and others. It is called the Lorentz force.