In a Coolidge tube, the potential difference across the tube is 20 kV, and 10 mA current flows through the voltage supply. Only 0.5 % of the energy carried by the electrons striking the target is converted into X-rays. The X-ray beam carries a power of
(a) 0.1 W
(b) 1 W
(c) 2 W
(d) 10 W
Correct Answer is: (b) 1 W
Power drawn by the Coolidge tube = (20 x 103 V)(10 x 10-3 A)
= 200 W.
Power of X-ray beam = 0.5/100 x 200 W = 1 W.