Question

A current is established in a gas discharge tube when a sufficiently high potential difference is applied across the two electrodes in the tube. The gas ionizes; electrons move away from the negative terminal and singly charged positive ions move away from the positive terminal.

(a) What is the current in a hydrogen discharge tube in which 2.9 ✕ 10¹⁸ electrons and 1.5 ✕ 10¹⁸ protons move past a cross-sectional area of the tube each second? (Enter the magnitude.)
A

(b) What is the direction of the current density ?

away from the negative terminal

away from the positive terminal    

Answer 1

Number of electrons, N1 = 2.9 x 10^18

Number of protons, N2 = 1.5 x 10^18

(a) The current would be the net flow of charge so you have N1 + N2 charge/second.

Means,

2.9 x 10^18 + 1.5 x 10^18 = 4.4 x 10^18 charge/sec.

Since one amp is 6.241 x 10^18 charges/second.

Therefore, the required current in the hydrogen tube = (4.4 x 10^18) / (6.241 x 10^18) = 0.705 A (Answer)

(b) Direction of current density is the direction of current.

Current flows from positive terminal to the negative terminal.

Hence, second option, 'away from the positive terminal' is the correct answer.