A cathode ray tube contains a pair of parallel metal plates `1*0cm` apart and `3*0cm` long. A narrow horizontal beam of electrons with velocity of `3xx10^7ms^-1` is passed down the tube mid way between the two plates. When the potential difference of `550V` is maintained across the plates, it is found that the electron beam is so deflected that it just strikes the end of one of the plates. Find the specific charge of an electron.

Explanation

Here, `y=1/2cm=0*5xx10^-2m`,
`l=3cm=3xx10^-2m, v=3xx10^7ms^-1`,
`d=1*0cm=10^-2m, V=550V`
Time to cross the tube,
`t=l/v=(3xx10^-2)/(3xx10^7)=10^-9s`
`y=1/2at^2=1/2((Ee)/(m))t^2=1/2((V//d)e)/(m)t^2`
or `e/m=(2yd)/(Vt^2)=(2xx(0*5xx10^-2)xx10^-2)/(550xx(10^-9)^2)`
`=1*8xx10^(11)Ckg^-1`