Physics

Henri Becquerel discovered natural radioactivity in 1896 when he observed that uranium salts emitted rays that could expose photographic plates. This was the first evidence of natural radioactivity.

Silicon and Germanium are the two primary semiconductor elements commonly used in making transistors due to their suitable electrical properties. Boron and aluminium are dopants, not base materials, and iridium and tungsten are metals not used for transistors.

Ultrasound waves have frequencies above the audible range for humans, which is typically above 20 kHz. Therefore, option A correctly states that ultrasound frequency is above 20 kHz.

Atmospheric pressure is defined as the force exerted per unit area by the weight of the air column above that area. Therefore, it is determined by the weight of the vertical column of atmospheric gases.

FM in radio stands for Frequency Modulation, which is a method of encoding information in a carrier wave by varying its frequency. This is the correct and widely accepted meaning of FM in radio communications.

According to quark theory, there are six types (flavors) of quarks: up, down, charm, strange, top, and bottom. These are considered elementary particles within the Standard Model of particle physics.

The ionosphere's density is higher during the daytime near the planetary surface due to solar radiation ionizing atmospheric particles. At night, the ionosphere's density decreases as ionization reduces, allowing radio waves to travel longer distances due to lower absorption and reflection changes.

A spectroscope is an optical instrument used to measure the properties of visible light by separating it into its component wavelengths or spectrum. This allows analysis of the light's properties, unlike microscopes, telescopes, or oscilloscopes which serve different purposes.

Kinetics is the branch of mechanics that deals with the motion of objects and the forces causing that motion, making option A the correct answer.

A bird on a high tension wire does not get electrocuted because it does not complete a circuit; there is no closed path for current to flow through its body to the ground.