A n-type silicon sample of width `4xx10^(-3)m`, thickness `25xx10^(-5)m` and length `6xx10^(-2)m` carries a current of 4.8 mA when the voltage is applied across the length of the sample. If the free electron density is `10^(22)m^(-3)`, then find how much time does it take for the electrons to travel the full length of the sample? Given that charge on an electron `e=1.6xx10^(-19)C`

Explanation

The current density J is given by
` J= (I )/(A ) = ( 4.8 xx 10^(-3))/(( 4 x 10^(-3)) ( 25 xx 10^(-5)) )= ( 4.8 xx 10^(-3))/( 10^(-6))`
The drift velocity `v_d` is given by
` v_d = (J )/( n e) = ( 4800 )/( 10 ^(22) xx 1.6 xx 10^(-19))= 3m//s`
The time taken t is given by
`t=(L )/(u_d ) =( 6 xx 10^(-2))/( 3 ) = 0.02 sec `