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Physics for Scientists and Engineers: A Strategic Approach with Modern Physics
Found in: Page 1082

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Short Answer

9. Electrons pass through the parallel electrodes shown in FIGURE EX37.9 with a speed of m/s towards left. What magnetic field strength and direction will allow the electrons to pass through without being deflected? Assume that the magnetic field is confined to the region between the electrodes.

Magnetic field will be tesla and is directed into the plane of paper.

See the step by step solution

Step by Step Solution

Step 1. Given information 

Given values are :-Voltage =V, Length=mm, Width= cm ,Speed=m/s towards left.
We have to find the magnetic field and its direction which will cancel the force due to electric field on electrons so that the electron can pass without being deflected.

 Step 2. simplify

Electric field E=

The upper plate is at a higher potential so Electric field will be in downward direction .

But electron being negatively charged will have a force in upward direction of magnitude q E .

Magnetic force on electron is given by where B is magnetic field.

Since electron is going left and we need the resulting magnetic force to be in downward direction (opposite to electric field) so that net force is zero.

BY using right hand rule we can see that magnetic field is directed into the plane of paper.

Comparing magnitudes

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