Physics

The iron needle floats on water when placed gently because of surface tension, which creates a 'skin' on the water surface that resists the needle's weight and prevents it from sinking. The needle's density is greater than water, so density difference is not the reason.

In a vacuum, all electromagnetic waves—including ultraviolet, infrared, and microwaves—travel at the same speed, which is the speed of light (approximately 3×10^8 m/s). Sound waves, however, are mechanical waves that require a medium to propagate and cannot travel through a vacuum. Therefore, their velocity in vacuum is effectively zero, which is less than the velocity of any electromagnetic wave. Hence, among the given options, sound waves have the smallest velocity in vacuum.

According to Boyle's law, pressure and volume of a gas are inversely proportional at constant temperature. Therefore, if the pressure is doubled, the volume becomes half.

Geophysics is the branch of physics that studies the physical properties and internal structure of the Earth, including its composition, dynamics, and processes.

The Paschen series corresponds to electron transitions to the n=3 energy level in hydrogen and emits lines in the infrared region. The Lyman series is a line spectrum in the ultraviolet, not continuous. The Balmer series is visible light, not ultraviolet. The spectral series formula is derived from the Bohr model, not the Rutherford model.

The turning effect of a force about a pivot point is called torque. It is the measure of how much a force causes an object to rotate.

The gravitational acceleration at the surface of the Sun is approximately 274 m/s². This value is well established and confirmed by multiple authoritative sources including NASA and educational physics resources. The original question's correct answer should be 'A' (274 m/s²). The option 'D' (None of these) is incorrect because the value 274 m/s² is the accepted standard for the Sun's surface gravity.

The Joule-Thomson effect describes the temperature change of a real gas when it expands suddenly through a porous plug or valve without exchanging heat with the environment, typically resulting in cooling or heating depending on the gas and initial conditions. This effect is fundamentally based on the sudden expansion of gases.

In nuclear fission, a massive nucleus splits into smaller fragments, releasing energy. Option B correctly describes this process, while option A describes fusion, which is the joining of nuclei.

The farad is the SI unit of capacitance, which measures a capacitor's ability to store charge per unit voltage. It is named after Michael Faraday.