Chapter 12 Magnetic Effects of Electric Current Questions-04
Questions
1. Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)
(a) mass
(b) speed
(c) velocity
(d) momentum
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Answer
(c) and (d)
When a proton enters in a region of magnetic field, it experiences a magnetic force. As a result of the force, the path of the proton becomes circular. Hence, its velocity and momentum change.
2. In Activity, how do we think the displacement of rod $A B$ will be affected if (i) current in rod $AB$ is increased, (ii) a stronger horse-shoe magnet is used, and (iii) length of the rod $A B$ is increased?
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Answer
(i) The displacement of rod AB increases when current is increased. This is because the magnetic force experienced by the rod increases with increased current leading to larger displacement of the rod.
(ii) The displacement of rod AB increases when a stronger horse-shoe magnet is used. This is because the magnetic force experienced by the rod increases with increase in the strength of magnetic field leading to larger displacement of the rod.
(iii) The displacement of rod AB increases when its length is increased. This is because the magnetic force experienced by the rod increases with increased length leading to larger displacement of the rod.
3. A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is
(a) towards south
(b) towards east
(c) downward
(d) upward
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Answer
(d) upward
The direction of the magnetic field can be determined by the 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. Since the direction of positively charged alpha particle is towards west, the direction of current will be the same i.e., towards west. Again, the direction of magnetic force is towards north. Hence, according to Fleming’s left hand rule, the direction of magnetic field will be upwards.
