Question

Which of the following has least penetrating power?
A. Alpha particles
B. Gamma rays
C. Beta particles
D. All have the same penetrating power

Answer 1

Hint: The penetrating power of particles depends upon the energy carried by them, their mass and their charge. A particle which has a larger mass and charge will interact with the medium through which it travels and lose energy through this interaction. The loss of energy means that the particle will have a lesser ability to penetrate into another medium.

Complete step by step answer:
The penetrating power of a particle refers to its ability to enter into another medium with greater effect. The penetrating power of a particle depends upon the energy carried by it, its mass and the charge carried by it.
A particle with a greater energy can use it to force itself into another medium and thereby penetrate it. A particle with a greater mass and charge will interact with the medium in which it travels. These interactions lead to a loss in the energy of the particle and hence, a loss in its penetrating power.
Alpha particles are positively charged helium nuclei. Hence, in comparison to beta particles and gamma rays, they have considerable mass and charge and hence, they have the least penetrating power.
Beta particles are fast moving electrons that have a negative charge. Thus, they also have mass and charge and thus are less penetrating than gamma rays but more penetrating than alpha particles.
Gamma rays are made up of pure energy photons that have no mass or charge. Hence, they do not interact with the medium they are travelling in and rarely have any loss in their huge energy. Therefore, they have the most penetrating power.
Therefore, the correct option is A) alpha particles.

Note: Students can remember that gamma rays have huge energy by recalling that they are placed at the end of the electromagnetic spectrum, having energy even greater than X-rays. They can imagine how penetrating gamma rays can be if they are much more penetrating than even X-rays, which can penetrate human skin and flesh.
The reason why nuclear explosions are so harmful is that a lot of gamma radiation is released which penetrates into all the surroundings and stays for many years and causes a lot of defects and destruction. Japan still reels from the effects of gamma radiation from the nuclear bombs dropped on it decades ago.