NCERT Solution for Class 10 Science Chapter 13
Magnetic Effects of Electric Current
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Exercises Questions
Page No-241
Questions No-10
Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?
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An electron beam moving horizontally from back wall towards the front wail is equivalent to a current flowing in the opposite direction (i.e., from front wall towards the back wall). The deflection of electron beam as seen by observer is to his right side and is shown in Figure. On applying Fleming’s left-hand rule we find that the magnetic field is acting in vertically downward direction.
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The direction of the magnetic field is determined by Fleming’s left hand rule. Magnetic field inside the chamber will be perpendicular to the direction of current and direction of deflection either upward or downward. The direction of current is from the front wall to the back wall because negatively charged electrons are moving from the back wall to the front wall. The direction of magnetic force is rightward. By using Fleming’s left hand rule, it can be concluded that the direction of magnetic field inside the chamber is downward.
Here, the electron beam is moving towards the viewer, i.e. out of the plane of the page. This means that the direction of current is towards the page. This shows the direction in which the forefinger is pointing. The thumb is pointing towards right which is same as the direction of deflection. The middle finger is pointing downwards; which shows the direction of the magnetic field.