A charged particle having charge `10^-6` C and mass of `10^-10` kg is fired from the middle of the plate making an angle `30^@` with plane of the plate. Length of the plate is `0.17 m` and it is separated by `0.1 m`. Electric field `E = 10^-3N/C` is present between the plates. Just outside the plates magnetic field is present. Find the velocity of projection of charged particle and magnitude of the magnetic field perpendicular to the plane of the figure, if it has to graze the plate at C and A parallel to the surface of the plate. (Neglect gravity)

Options

A. `3.4mT`
B. `4.3mT`
C. `2.3mT`
D. `5.3mT`

Answer

A

Explanation

Since, `a=(qE)/(m)`
`=((10^(-6))(10^(-3)))/((10^(-10)))=10ms^(-2)`
`(`downwards `)`
Path of the partical is a parabola. The particle will graze at Q if,
length of the plates `=("Range")/(2)=(u^(2)sin2theta)/(2g)`

`implies0.17=(u^(2)sin(2theta))/(2g)=(u^(2)sin60^(@))/(20)`
`impliesu=1.98ms^(-1)`
Speed of particle at Q is ,
`upsilon=ucos theta=1.98cos 30^(@)=1.7ms^(-1)`
It will graze at P if,
`PQ=2` ( radius of circular path in magnetic field )
`implies0.1=2((m upsilon)/(qB))`
`impliesB=(2xx10^(-10)xx1.7)/(0.1xx10^(-6))=3.4xx10^(-3)T=3.4mT`