State Fleming’s left hand rule.

Hint: When a charged particle is present in a magnetic field it experiences a force upon it. Fleming’s left-hand rule is used to find the direction of the force vectors acting on the charged particle with respect to the direction of the magnetic field and current in the system.

Complete step-by-step answer:
The electric charges moving in a magnetic field tends to experience a force, while no such force is experienced by the rest or static charges. This phenomenon was first discovered by a Dutch Physicist Hendrik Antoon Lorentz.
The force acting on the charged particle is proportional to the magnitude of the magnetic field, also directly proportional to the charge and it is directly proportional to the component $v$of velocity in the perpendicular direction of the field.
This force deflects the charged particle sideways and is known as the magnetic Lorentz force.
Mathematically, it is given by:
$\vec F = q\left( {\vec v \times \vec B} \right)$
The directions of magnetic Lorentz force $\vec F$ can be determined by using the following rule:
FLEMING’S LEFT RULE
Stretch the thumb and the first two fingers of the left hand in such a way that they are mutually perpendicular to each other. If the forefinger points in the direction of the magnetic field, central finger in the direction of the current, then the thumb gives the direction of force acting on the charged particle.
The following diagram shows the Fleming’ left hand rule visually:


Note: There is another rule to help find the direction of the Lorentz force acting on the charged particle, namely the right-hand palm rule. This rule states that if we open our right hand’s palm and place it so that the tip of our fingers point in the direction of the magnetic field and the thumb in the direction of the velocity of the positive charge, then the palm faces the direction towards the force.