A positively charges particle (alpha particle) projected towards west is deflected towards north by a magnetic field . The direction of magnetic field is ……

Options

A. towards south
B. towards east
C. downward
D. upward

Answer

D

Explanation

Here the positively charged particle (alpha particle ) is initially moving towards the west .
The deflection of alpha particle is towards north . This shows that the magnetic force acts on it towards the north (direction).
Hence , here (a) direction of current I is towards west and (b) direction of force F is towards north .

let us now hold the first (force) finger , middle finger and thumb of your left hand at right angles to one another .
Adjust the left hand in such a way that your middle finger point towards the west ( in the direction of the current ) and the thumb points towards the north ( in the direction of the force).
In this case , your first (force) finger points upwards (shown by the symbol ). Since the direction of the forefinger gives the direction of the magnetic field , the magnetic field would be in the upward direction .[see figure 13.23 (a) or 13.23 (b)].