Physics

Radioactivity was discovered by Henri Becquerel in 1896 when he found that uranium salts emitted rays that could fog photographic plates. This discovery was foundational in nuclear physics.

If a rocket's launch velocity is less than Earth's escape velocity, it does not have enough kinetic energy to overcome Earth's gravitational pull and will eventually fall back to Earth. Escape velocity is the minimum speed needed to break free from the planet's gravity without further propulsion.

Escape velocity depends on both the mass and radius of the planet or celestial body from which an object is escaping. The formula for escape velocity is v = sqrt(2GM/R), where G is the gravitational constant, M is the mass of the planet, and R is its radius. It does not depend on the mass of the object trying to escape or the velocity of the rotating planet. Therefore, the correct answer is that escape velocity depends on both the mass and radius of the planet or celestial body.

To escape the surface of a celestial body, an object must have kinetic energy greater than or equal to the gravitational potential energy (in magnitude) binding it to the body. This ensures the object can overcome the gravitational pull and not fall back.

Dark matter is invisible to telescopes because it does not interact with electromagnetic forces, meaning it neither emits, absorbs, nor reflects light. This lack of interaction with electromagnetic radiation makes it undetectable by conventional telescopes.

A light year is the distance that light travels in one year, making it a unit of distance, not time, energy, or mass.

A rainbow is formed due to the combined effects of refraction (bending of light entering water droplets), dispersion (splitting of light into colors), and total internal reflection (light reflecting inside the droplet). Hence, all these phenomena are involved.

Neutrons and protons in an atomic nucleus are held together by the strong nuclear force, often referred to as exchange forces, which is much stronger than gravitational, Coulombic, or magnetic forces at this scale.

The scale height (H) is defined as the height over which the atmospheric pressure decreases by a factor of e (approximately 2.71828). This is a standard concept in atmospheric physics describing how pressure decreases exponentially with altitude.

Helium was first discovered in the solar chromosphere during a solar eclipse in 1868, identified by its unique spectral lines before it was found on Earth. This makes it the first element discovered in the sun's chromosphere.