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Physics Question on Atoms

An electron starts from rest and travels 0.9 m in an electric field of 200 V/m. After this, it enters a magnetic field at right angles to its direction of motion If the radius of circular path of the electron is 9 cm, the magnetic field induction is (Given e=1.6×10−19C,m=9×10−31Given\, e=1.6 \times 10^{-19}C, m=9\times 10^{-31} kg)

A

5×10−4wb/m25 \times 10^{-4}wb/m^2

B

5×10−5wb/m25 \times 10^{-5}wb/m^2

C

5×10−3wb/m25 \times 10^{-3}wb/m^2

D

5×10−2wb/m25 \times 10^{-2}wb/m^2

Answer

5×10−4wb/m25 \times 10^{-4}wb/m^2

Explanation

Solution

V2−U2=2asV^2 - U^2 = 2 as V2=2EqmS ⇒ V=2EqmSV^2 = 2 \frac{Eq}{m} S \, \Rightarrow \, V = \sqrt{2\frac{Eq}{m} S} r=mVBq ⇒ B=mVrqr = \frac{mV}{Bq} \, \Rightarrow \, B = \frac{mV}{rq}