A positively-charged particle (alpha-particle) projected towards the west is deflected towards north by a magnetic field. The direction of magnetic field is 1. towards south 2. towards east 3. downward 4. upward

Solution:

The direction of the magnetic field can be determined using Fleming’s Left-hand rule. According to the rule, if we arrange our thumb, forefinger and the middle finger of the left hand right perpendicular to each other, then the thumb points towards the direction of the magnetic force, the middle finger the direction of current and the forefinger the direction of magnetic field. Since the direction of the positively charged particle is towards the west, the direction of the current will also be towards the west. The direction of the magnetic force is towards the north. Hence the direction of the magnetic field will be upward according to Fleming’s Left-hand rule.