Physics

Nuclear sizes are typically expressed in fermis, which is a unit equivalent to 10^-15 meters, commonly used in nuclear physics to measure nuclear dimensions.

The speed of sound in air depends primarily on temperature. At 20°C (room temperature), the speed of sound in air is approximately 343 m/s, which converts to about 1235 km/h (343 m/s × 3.6 = 1234.8 km/h). This is the commonly accepted average value under standard conditions. The formula to estimate speed of sound in air is c = 331.3 + 0.606 × T (in m/s), where T is temperature in °C. Multiplying by 3.6 converts m/s to km/h. Therefore, the correct answer is option C (1235 km/h). Option A (1347 km/h) is not a standard or typical value for speed of sound in air at normal conditions.

The farad (F) is the SI unit of capacitance, which measures a capacitor's ability to store charge per unit voltage. Therefore, option C is correct.

Sounds with frequencies below 20 Hz are called infrasonic waves. This is because the human audible range starts from about 20 Hz, so frequencies below this are termed infrasonic.

A capacitor (capacitance) blocks direct current (DC) because it does not allow a steady flow of charge through it, effectively acting as an open circuit for DC while allowing alternating current (AC) to pass.

Fission reactions produce the most harmful radiation compared to fusion, chemical, or photo-chemical reactions. When a heavy nucleus undergoes fission, it splits into smaller nuclei and emits high-energy neutrons, gamma rays, and other ionizing particles. It also creates a variety of long-lived radioactive fission products that can cause significant biological damage and environmental contamination. Fusion reactions, while producing very high-energy radiation such as neutrons and gamma rays, generally produce fewer radioactive by-products and are considered to produce less harmful radiation overall. Chemical and photo-chemical reactions involve only electron rearrangements and do not emit ionizing radiation.

Heinrich Hertz was the first scientist to successfully generate and detect electromagnetic waves, proving Maxwell's theory experimentally. Thomas Edison did not work on electromagnetic waves, and the others are known for different contributions.

Velocity is defined as the speed of an object in a specific direction, distinguishing it from speed which is scalar and directionless. Therefore, the speed of an object in one direction is called velocity.

The intensity of the Earth's gravitational field is maximum at the poles because the Earth is an oblate spheroid, causing the poles to be closer to the Earth's center of mass than the equator. This results in a stronger gravitational pull at the poles compared to the equator or surface in general.

As you descend into a well, you move closer to the Earth's center, where the gravitational force slightly decreases, causing your weight to slightly decrease.

The time period of a pendulum depends on the acceleration due to gravity. Since the Moon's gravity is weaker than Earth's, the pendulum's time period increases when taken to the Moon.

Atomic power plants generate energy primarily through nuclear fission, where heavy atomic nuclei split into smaller nuclei, releasing a large amount of energy. Fusion is not yet used in commercial power plants, and thermal combustion is unrelated to atomic power generation.

A transformer operates on the principle of mutual induction, where a changing current in the primary coil induces a voltage in the secondary coil through a shared magnetic field.

The angle of friction is the angle made between the normal reaction and the resultant reaction when a body is on the verge of sliding, and the angle of repose is the maximum angle at which a body can rest without sliding. These two angles are equal for a given surface and material.

Since the car is moving at a constant speed and the ball is thrown straight up, the ball retains the horizontal velocity of the car and falls back into the boy's hand.

A geostationary satellite orbits the Earth with a period equal to the Earth's rotational period, which is 24 hours. This allows the satellite to remain fixed over one point on the equator.

The velocity of sound in air primarily depends on temperature, moisture content, and wind conditions. However, under normal atmospheric conditions, changes in air pressure do not significantly affect the speed of sound because both the density and elasticity of air change proportionally, leaving the speed nearly constant.

Among the four fundamental forces, gravitational force is the weakest. Electrostatic, magnetic, and nuclear forces are significantly stronger at the particle level.

Adiabatic demagnetisation is a principle used to achieve very low temperatures by reducing the magnetic field on certain materials, causing their temperature to drop. This method is commonly used in cryogenics to reach temperatures near absolute zero.

A pulsar is a highly magnetized, rotating neutron star that emits beams of electromagnetic radiation. This radiation can be observed when the beam is pointed toward Earth, making neutron stars the correct identification for pulsars.

The SI unit of illumination is the lux, which measures luminous flux per unit area. Candela is the unit of luminous intensity, and flux refers to luminous flux measured in lumens.

An Angstrom is a unit of length equal to 10^-10 meters, commonly used to measure atomic and molecular scales, such as wavelengths of light and sizes of atoms.

The Doppler effect applies to both light waves and sound waves, as it describes the change in frequency or wavelength of a wave in relation to an observer moving relative to the source of the waves.

The first controlled nuclear fission of an atom was carried out in Germany in 1938 by Otto Hahn and Fritz Strassmann, who discovered nuclear fission of uranium. This discovery marked the beginning of nuclear physics research leading to controlled fission.

According to Einstein's theory of relativity, the speed of light in a vacuum is always constant and does not change regardless of the observer's frame of reference. Length, time, and space can vary depending on relative motion, but the velocity of light remains invariant.