7.) In an attempt to reproduce J. J. Thomson’s experiment, it is seen that an el

Question

7.) In an attempt to reproduce J. J. Thomson’s experiment, it is seen that an electron with kinetic energy 2.5 x 10 3 eV passes undeflected through a region in which there is a downward-directed uniform electric field of magnitude 10 x 10 3 N/C and a crossed magnetic field. Ignore the minor effects of the gravitational field. [1eV = 1.6 x 10 -19 J]

            (a) What is the magnitude of the magnetic field?

            (b) If a proton were to pass through the same region, what would happen to the     magnetic and electric forces it experiences in relation to those that an electron       experiences? No calculations are necessary and a qualitative statement of the    differences, with a very brief explanation, is sufficient.

            (c) Is it possible for the proton to pass through this combination of fields    undeflected? If so, under what circumstances? Again, no calculations are     necessary.

Explanation / Answer

here ,

let the magnetic field is B

a) for the electrons to pass undeflected

q * E = sqrt(KE* 2/m) * q * B

B * sqrt(2.5 *10^3 * 1.602 *10^-19/(2 * 9.11 *10^-31)) = 10 *10^3

solving for B

B = 6.745 *10^-4 T

the magnetic field is 6.745 *10^-4 T

b)

for the same kinetic energy , the velocity of the proton will be lower. and hence , there will be magnetic force smaller than the electric force

c)

yes , it is possible for the proton to pass through this combination of fields undeflected.

the velocity of the proton should be increased so that magnetic force and electric force must be balanced

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