Physics

Gamma rays (γ-rays) have high penetration power, allowing them to reach infections inside the body effectively, unlike alpha or beta rays which have low penetration. X-rays also penetrate but are less commonly used for treating infections compared to gamma rays in medical therapies.

X-rays and gamma rays (γ-rays) are both types of electromagnetic waves, differing mainly in their origin and energy. Therefore, X-rays are electromagnetic waves like γ-rays.

A meter rod generally has a least count of 1 mm (0.001 m), so measurements should not be recorded beyond three decimal places in meters. Record (i) is too precise, while (iii) implies an accuracy not possible with a standard meter rod. Therefore, 0.21 m is the most appropriate recorded value.

The mass of a neutron is approximately 1.67 x 10^-27 kilograms, which is close to the mass of a proton and much larger than the mass of an electron.

TV sets primarily emit very low-level non-ionizing electromagnetic radiation, mainly in the radio-frequency range, with older cathode-ray tube (CRT) TVs capable of emitting very low levels of X-rays, but these are limited to background levels and are not harmful. Microwave ovens emit non-ionizing microwave radiation at about 2.45 GHz, which is far lower in energy than gamma rays. They are designed with safety features to prevent microwave leakage beyond strict regulatory limits. Therefore, TV sets and microwave ovens do not emit gamma rays (γ-rays), but rather non-ionizing radiation, with TV sets potentially emitting very low-level X-rays in older models. Among the options given, X-rays (A) is the closest correct answer for TV sets, while microwave ovens emit microwaves, which are not listed as an option. The original answer (D) gamma rays is incorrect.

Alpha particles consist of two protons and two neutrons, giving them a net positive charge of plus two. Therefore, the correct answer is 'Plus two'.

Mass defect per nucleon is defined as the packing fraction, which represents the mass defect divided by the total number of nucleons. It is a measure of the average mass defect per nucleon in a nucleus.

The maximum safe radiation dose limit for persons working in a nuclear power station is generally set at 5 rem (50 millisieverts) per year, not per week. This corresponds to about 0.1 rem per week on average. The options given in the question are weekly dose limits, which are not standard. However, among the options, 5 rem per week (option B) is the only one that matches the internationally recognized annual dose limit of 5 rem (50 millisieverts) when considered over a year (5 rem/week × 52 weeks = 260 rem/year, which is much higher than the annual limit, so the weekly framing is misleading). The standard regulatory limit is 5 rem per year, so none of the weekly values are strictly correct. But since the question asks for a weekly limit, 5 rem per week is the closest to the correct annual limit. Therefore, the correct answer is B.

A body in equilibrium experiences no net force, so it can either be at rest or move with uniform velocity (constant speed in a straight line). Hence, it may be at rest or in uniform motion.

An alpha particle ionizes an atom primarily through direct collision with the atom's electrons, knocking them out and creating ions. Electrostatic forces (attraction or repulsion) influence the interaction but ionization occurs mainly due to the direct impact.