Question

An X-ray tube is operating at $150kV$ and $10mA$. If only $1\text{\%}$ of the electric power is converted into X-rays, the rate at which the target is heated, in $cal{s}^{-1}$, is

• A. $3.57$
• B. $35.7$
• C. $4.57$
• D. $15$

Answer 1

The correct option is A $3.57$

$V=150KV$
$I=10mA$
$Power=VI=1500W$
Efficiency of tube $=0.01$

Heat supplied = $0.01\times 1500W=15W=15J/s=3.57cal/s$

(use 1 cal = 4.18 J)