When a

**charged particle**moves along a

**magnetic field**line into a region where the

**field**becomes stronger, the

**particle**experiences a force that reduces the component of velocity parallel to the

**field**. This force slows the

**motion**along the

**field**line and here reverses it, forming a

**Magnetic Mirror**. Motion of a charged particle in magnetic field is characterized by the change in the direction of motion. It is expected also as magnetic field is capable of only changing direction of motion. In order to keep the context of study simplified, we assume magnetic field to be uniform. This assumption greatly simplifies the description and lets us easily visualize the motion of a charged particle in magnetic field.

**Motion of a Charged Particle in a Magnetic Field**Motion of a charged particle when it is moving collinear with the field magnetic field is not affected by the field (i.e. if motion is just along or opposite to magnetic field) ( : $: \quad F=0$ ) Only the following two cases are possible:

**Case I: When the charged particle is moving perpendicular to the field**The angle between $\overrightarrow{\mathrm{B}}$ and $\overrightarrow{\mathrm{v}}$ is $\theta=90^{\circ}$ So the force will be maximum ( $=$ qvB ) and always perpendicular to motion (and also field); Hence the charged particle will move along a circular path (with its plane perpendicular to the field). Centripetal force is provided by the force qvB,

**case II**: The charged particle is moving at an angle $\theta$ to the field : $\left(\theta \neq 0^{\circ}, 90^{\circ} \text { or } 180^{\circ}\right)$ Resolving the velocity of the particle along and perpendicular to the field. The particle moves with constant velocity v cos $\theta$ along the field ($\because$ no force acts on a charged particle when it moves parallel to the field). And at the same time it is also moving with velocity $v$ sin $\theta$ perpendicular to the field due to which it will describe a circle (in a plane perpendicular to the field)

**Also Read:**Biot Savart’s Law

**Click here for the Video tutorials of Magnetic Effect of Current Class 12**

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