A particle moves in a circle of diamater 1.0 cm under the action of magnetic field of 0.40 T, An electric field of `200 V m^(-1)` makes the path straight. Find the charges/mass ration of the particle.

Options

A. `2.5xx10^(3)C//kg`
B. `2xx10^(3)C//kg`
C. `3.5xx10^(5)C//kg`
D. `3xx10^(5)C//kg`

Answer

A

Explanation

When only magnetic field will act path will be circular, but if an electric force acts opposite of magnetic force then velocity of particle would be in striaght line. Hence `F_(M)=qvB` and `F_(E)=qE`

By
`F_(M)=F_(E)impliesqvB=qE-(mv^(2))/(R)" "......(1)`
So by equation `(1)(q)/(m)=(v)/(RB)`
Also `(q)/(m)=(v^(2))/(RE)" "......(2)`
`qvB=qE,v=(E)/(B)+(200)/(0.40)=500m//s`
Now by eaution `(2)`
`(q)/(m)=((500)^(2))/(((1)/(2))xx200)=2.5xx10^(3)C//kg`