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Problem 11: An electron with an initial speed of 29 × 105 m/s is fired in the same direction as a uniform electric field of 80 N/C. How far does the electron travel before brought to rest and turned back?


Since electron has negative charge, therefore, it will be retarded in the given conditions. Using the equation F = q0E (Force on the electron in the electric field)  and then equating with F = ma. Remember that charge on an electron is 1.6 × 10-19 C.

Now mass of an electron is 9.1 × 10-31 Kg, therefore,

Here the negative sign accounts for the direction of the acceleration (retardation).

Now to find the distance the electron covers before coming to rest (vf = 0) can be calculated by using the equation of motion, 2as = vf2 – vi2. Put the values,


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