A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is
NCERT Solution for Class 10 Science Chapter 13
Magnetic Effects of Electric Current
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Intext Questions
Page No-232
Questions No-3
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(d) upward
In accordance with Fleming’s left-hand rule, the direction of magnetic field is vertically upward.
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(d) The direction of the magnetic field can be determined by applying Fleming’s left hand rule. According this rule, if we arrange the thumb, the centre finger, and the forefinger of the left hand at right angles to each other, then the thumb points towards the direction of the magnetic force, the centre finger gives the direction of current, and the forefinger points in the direction of magnetic field. As the direction of a positively charged alpha particle is towards west, the direction of current will be the same i.e., towards the west. If the direction of magnetic force is towards the north. Hence, according to Fleming’s left hand rule, the direction of the magnetic field will be upwards.
This question can be solved by using Fleming’s Left Hand Rule. We know that the direction of current is opposite to the direction of electron’s movement and hence it would be same as the direction of proton’s movement. So, the direction of current is towards west. As per Fleming’s Left Hand Rule; the middle finger shows the direction of current, the forefinger shows the direction of magnetic field and the thumb shows the direction of motion. Here, the deflection is towards north, i.e. in north westerly direction and hence, the direction of magnetic field would be towards north, i.e. upward.
The deflection of a positively charged particle in a magnetic field is described by the right-hand rule. According to the right-hand rule:
If you point your thumb in the direction of the velocity of the positively charged particle (alpha particle in this case), and your index finger in the direction of the magnetic field, then the middle finger will point in the direction of the force experienced by the particle.
In this scenario:
» Particle (alpha-particle) is projected towards west.
» The deflection is towards north.
So, if you use the right-hand rule, you would point your thumb to the west, your index finger to the north (since the particle is deflected towards the north), and your middle finger will then point in the direction of the magnetic field. Therefore, the direction of the magnetic field is upwards (towards the sky).