The electron-beam current in an X-ray tube is 3.2 mA. Assume every electron emitted by the cathode reaches the target. Take the magnitude of electronic charge as 1.6×10⁻¹⁹ C. If the number of electrons striking the target each second is N×10¹⁶, find N.
Physics · Atomic Structure and X-rays · x-rays and its types
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Question

The electron-beam current in an X-ray tube is 3.2 mA. Assume every electron emitted by the cathode reaches the target. Take the magnitude of electronic charge as 1.6×10⁻¹⁹ C. If the number of electrons striking the target each second is N×10¹⁶, find N.

Physics · Atomic Structure and X-rays · x-rays and its types

G1 Physics · Accepted Answer

Electric current is charge passing per unit time. If n electrons strike the target each second, I = ne. Therefore, n = I ÷ e. Substitute: n = 3.2×10⁻³ ÷ (1.6×10⁻¹⁹) = 2.0×10¹⁶ s⁻¹. Thus the number of electrons per second is 2×10¹⁶. Hence N = 2.