Physics

The gravitational acceleration near the surface of the Earth is approximately 9.80 m/s², which is the standard value used in physics for Earth's gravity.

The performance of a refrigerator is specifically described by its coefficient of performance (COP), which measures the ratio of heat removed from the cold reservoir to the work input. While 'efficiency' is a general term, COP is the precise term used for refrigerators.

Rutherford's atomic model could not explain the behavior of electrons, particularly why they do not spiral into the nucleus despite acceleration, which classical physics predicted. This limitation led to the development of the Bohr model.

A mirage occurs due to the refraction of light and total internal reflection in layers of air with varying temperatures, causing the light to bend and create the illusion of water or distant objects.

A current of one microampere (1 μA = 1×10⁻⁶ A) corresponds to a charge flow of 1×10⁻⁶ coulombs per second. Since one electron carries a charge of approximately 1.6×10⁻¹⁹ coulombs, the number of electrons per second is (1×10⁻⁶ C/s) ÷ (1.6×10⁻¹⁹ C/electron) ≈ 6.25×10¹² electrons per second.

The acceleration due to gravity on the Moon is approximately 1/6th that of Earth's gravity because the Moon's mass and radius are much smaller than Earth's, resulting in weaker gravitational pull.

The surface charge density (σ) is calculated by dividing the total charge (q) by the total surface area (A) of the cube. For a cube with side length 5 cm (0.05 m), the surface area is 6 × (0.05 m)² = 6 × 0.0025 m² = 0.015 m². Given the charge q = 6 C, the surface charge density is σ = q / A = 6 C / 0.015 m² = 400 C/m². This matches option D, not option A. Therefore, the correct answer is D.

At the highest point of a projectile launched at 45 degrees, all the kinetic energy is due to the horizontal component of velocity, which is constant. Since the initial kinetic energy is E, and the velocity components are equal at 45 degrees, the kinetic energy at the highest point is half of E, i.e., E/2.

Water has the highest specific heat capacity among the given substances, meaning it can absorb more heat per unit mass than alcohol, methane, or kerosene before its temperature rises.

Police officers commonly use radar guns, which emit radio waves, to measure the speed of approaching vehicles. The radio waves reflect off the car, and the change in frequency (Doppler effect) is used to calculate speed.