Physics

The CGS system (centimeter-gram-second) is a variant of the metric system and is also known as the Metric or French system of units, as it originated in France and is based on metric units.

The core of a transformer is laminated to reduce eddy current losses. Laminations increase the resistance to eddy currents, thereby minimizing energy loss due to circulating currents induced in the core.

The force of attraction between any two bodies due to their masses is called gravitational force. It is a fundamental force that acts between all masses in the universe.

Cadmium is a stable, non-radioactive element, whereas thorium, radium, and uranium are all naturally radioactive elements. Therefore, cadmium is the correct answer as it is not radioactive.

Raindrops fall through the air and eventually reach a terminal velocity, which depends on their size and shape. Different droplets have different terminal velocities, so they fall at different ultimate speeds.

TV audio signals are typically transmitted using frequency modulation (FM) because FM provides better noise immunity and sound quality compared to amplitude modulation (AM).

Newton's Third Law states that for every action, there is an equal and opposite reaction, which is exactly described in option A. The other options describe different physical laws unrelated to Newton's Third Law.

Light travels fastest in a vacuum and slows down when passing through denser media. Among the given options, glass has a higher refractive index than air and water, so light speed is minimum in glass.

A force is conservative if the work it does depends only on the initial and final positions of the particle, not on the path taken between them. This means the work done by the force is path-independent, which is the defining property of conservative forces.

In an isochoric process, the volume remains constant, so there is no displacement of the boundary. Since work done is given by W = PΔV, and ΔV = 0, the work done is zero.

Speed is a scalar quantity because it only has magnitude and no direction, whereas acceleration, displacement, and force are vector quantities with both magnitude and direction.

Moderators in nuclear reactors slow down fast neutrons to thermal energies, increasing the likelihood of fission. They do not bring neutrons to rest, absorb them, or reflect them primarily.

The efficiency of a Carnot engine is given by the formula η = 1 - (T_cold / T_hot), where temperatures must be in Kelvin. Converting 150°C and 50°C to Kelvin gives 423 K and 323 K respectively. Substituting these values, efficiency = 1 - (323/423) ≈ 0.235 or 23.5%, which rounds to 23.6%. Therefore, the correct answer is option C (23.6%). The original answer D (29.4%) is incorrect based on the calculation and standard thermodynamics principles.

The emf (E) induced in a self-inductance L is given by E = L * (dI/dt). Here, dI = 2 A - 3 A = -1 A, dt = 1 ms = 0.001 s, so dI/dt = -1000 A/s. Taking magnitude, L = E / |dI/dt| = 5 V / 1000 A/s = 0.005 H = 5 mH.

A flywheel smooths out the energy variations in an engine by storing rotational energy, and its added weight helps stabilize the engine's operation. Therefore, both A and B are correct purposes of a flywheel.

Potential energy is the energy stored in an object due to its position or configuration, such as height above the ground. This distinguishes it from kinetic energy, which is due to motion.

The gravitational acceleration on the Moon's surface is approximately 1.62 m/s², which is much less than Earth's 9.8 m/s². This value corresponds to option B.

In adiabatic compression, work is done on the system without heat exchange, causing the internal energy to increase. In contrast, adiabatic expansion decreases internal energy, and isothermal processes keep internal energy constant.

Increasing pressure raises the boiling point of a substance because higher pressure requires the substance's vapor pressure to be higher to boil, thus increasing the temperature at which boiling occurs.

For diatomic gases, the ratio of specific heats (γ) is approximately 1.4 under normal conditions, reflecting their degrees of freedom. This value is standard in thermodynamics for diatomic molecules like oxygen and nitrogen.

At a given temperature, the average kinetic energy of gas molecules is the same for all gases regardless of their type. This is because temperature is directly proportional to the average kinetic energy of the molecules.

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.

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.

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.

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.