In a hydrogen discharge tube it is observed that through a given cross-section 3.13 × 1015 electrons are moving from right to left and 3.12 × 1015 protons are moving from left to right. What is the electric current in the discharge tube and what is its direction 

(1) 1 mA towards right

(2) 1 mA towards left

(3) 2 mA towards left

(4) 2 mA towards right

(1)

 

For any cross-section

                                    

Current is opposite to flow of electrons
Let charge on each electron be qe and charge on each proton be qp

Flow of current due to electrons = ne qe    (right)
Flow of current due to protons = npqp       (right)
Total current = neqe+nqqp

I=neqe+npqp=1mA towards right 

Direction of current is taken as flow of positive charge.

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