Physics

One Torr is defined as exactly 1 millimeter of mercury (mmHg). This unit is commonly used to measure pressure and is equivalent to the pressure exerted by a 1 mm column of mercury.

Ole Roemer was the first to measure the velocity of light in 1676 by observing the eclipses of Jupiter's moons and noticing discrepancies in their timing, which he attributed to the finite speed of light. This was the first quantitative estimate of light's speed.

The average kinetic energy of the molecules of a body is directly proportional to its temperature, making temperature the correct answer. Heat refers to energy transfer, internal energy includes both kinetic and potential energies, and 'none' is incorrect.

Nickel is a ferromagnetic material, meaning it can be magnetized and attracted to magnets. Tungsten, aluminium, and copper are not ferromagnetic; they are either paramagnetic or diamagnetic.

In solids, particles primarily exhibit vibrational motion about fixed positions, but they can also have slight rotational and translational motions in some contexts. Therefore, all these types of motion can be present to some extent in solids.

One British Thermal Unit (BTU) is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit, which is approximately equal to 2055 Joules.

The density of pure water at around 4°C is approximately 997 kg/m³, which is the most accurate value among the options provided. This value is commonly used in scientific contexts for water density.

Primary cosmic rays are mostly composed of high-energy protons, which are charged particles originating from outer space. Neutrons, electrons, and gamma rays are present but in much smaller proportions compared to protons.

Cosmic rays are high-energy charged particles that are trapped and deflected by the magnetic fields in our galaxy, unlike alpha or gamma rays which are not confined by magnetic fields in the same way.

The Sun produces most of its energy through nuclear fusion, where hydrogen nuclei combine to form helium, releasing a tremendous amount of energy. Nuclear fission and burning hydrogen are incorrect processes for the Sun's energy production.