An electron moving horizontally with a velocity of `4xx10^4ms^-1` enters a region of uniform magnetic field of `10^-5T`, acting vertically downwards as shown in figure. Draw its trajectory and find out the time it takes to come out of the region of magnetic field.

Explanation

Here, `v=4xx10^4ms^-1`, `B=10^-5T` perpendicular magnetic field, is subjected to a semicircular trajectory inside the magnetic field and comes out as shown in figure. Radius r, of the ciruclar path of electron is given by

`(mv^2)/(r)=qvB` or `r=(mv)/(qB)`
`:. r=((9*1+10^(-31))xx(4xx10^4))/((1*6xx10^(-19))xx10^-5)`
`=22*75xx10^-3m`
Time taken to come out of the region of magnetic field is
`t=(pir)/(v)=((22//7)xx(22*75xx10^-3))/(4xx10^4)`
`=1*8xx10^-6s`