Question

50% of X-rays obtained from a Coolidge tube pass through 0.3 mm, thick aluminum foil. If the potential difference between the target and the cathode is increased, then the fraction of X-rays passing through the same foil will be-
$
  A)50\% \\
  B) > 50\% \\
  C) < 50\% \\
  D)0\% \\
 $

Answer 1

Hint: In order to solve this question, firstly we will understand the concept of Coolidge tube which is also known as cathode tube. Then we will compare all the given options to get the required answer.

Complete Step-by-Step solution:
We know that when we increase the accelerating potential between the filament and the target, the penetrating power of the X-ray will increase. As a result, the proportion of the X-ray passing through the foil would through.
The Coolidge tube is the forerunner of all the types of X-ray tubes in common use today. The Coolidge tube was the first practical type of x-ray tube that used the thermionic emission concept.
The potential depth for any wave is proportional to$\dfrac{1}{\lambda }$, so if we increase the voltage the wavelength decreases, so now more X-ray passes through the foil.
The penetrating strength of X-rays correlates directly with the electrons (V) 's accelerating potential or the X-ray energy.
But it is given that the same fraction of X-ray is passing. Therefore, the thickness of the aluminum foil should be increased to maintain the same fraction of the X-ray that will pass through the foil.
Therefore, we conclude that if the potential difference between the target and the cathode is increased, then the fraction of X-rays passing through the same foil will be >50%.
Hence, the correct option is B.

Note- While solving this question, we must know that the Coolidge tube was the first type of practical x-ray tube to employ the principle of thermionic emission. Also one must know that there are two designs in Coolidge tube i.e. window tubes and side-window.