Physics

Johannes Kepler formulated the three laws of planetary motion, describing the orbits of planets around the sun. This distinguishes him from Copernicus, who proposed heliocentrism, Newton, who formulated the law of universal gravitation, and Galileo, who made significant astronomical observations but did not enunciate these laws.

The SI unit of force is the Newton, which is defined as the force required to accelerate a one-kilogram mass by one meter per second squared.

Radiation is the transfer of energy through electromagnetic waves and does not require a medium, unlike conduction and convection which require a medium to transfer heat.

Red light has the longest wavelength among the visible spectrum colors listed, so it is deviated least when passing through a prism or similar medium due to less refraction compared to shorter wavelengths like blue or violet.

Gamma rays and X-rays are both forms of electromagnetic radiation with very short wavelengths and high energy, making them similar in nature. Alpha (a-rays) and beta (b-rays) rays are particles, not electromagnetic waves, and ultraviolet (U.V.) rays have longer wavelengths and lower energy than gamma rays.

Good absorbents of electromagnetic radiation are also good radiators because materials that absorb energy well tend to emit energy efficiently as well, according to Kirchhoff's law of thermal radiation.

The refractive index is a ratio of the speed of light in vacuum to the speed of light in the medium, making it a dimensionless quantity with no units.

Sounds with frequencies below 20 Hz are called infrasonic sounds. This is because the human hearing range typically starts at 20 Hz, so frequencies below this are termed infrasound.

Charles-Augustin de Coulomb discovered the law of attraction and repulsion between electric charges, formulating Coulomb's law which quantifies the force between charged objects.

As temperature increases, the conductivity of metals decreases because the increased thermal vibrations of the metal ions scatter the conduction electrons more, reducing their mobility.

A dyne is a unit of force in the centimeter-gram-second (CGS) system. It is defined as the force required to accelerate a mass of one gram at a rate of one centimeter per second squared.

Max Planck is famous for his discovery of energy quanta, which laid the foundation for quantum theory. He introduced the concept that energy is quantized, which is distinct from the photon concept introduced later by Einstein.

High-energy subatomic particles arriving from outer space are known as cosmic rays. They primarily consist of protons and atomic nuclei, but the term 'cosmic rays' specifically refers to these energetic particles from space.

Refraction of sound occurs when sound waves pass from one medium to another or when there is a variation in temperature or density within a medium, causing the sound waves to bend. Since both water and air can cause such refraction, the correct answer is 'Both A & B'.

Galileo Galilei is credited with the idea of the law of inertia, which states that an object in motion stays in motion unless acted upon by an external force. This concept laid the foundation for Newton's first law of motion.

In the cgs (centimeter-gram-second) system, surface tension is measured in dynes per centimeter (dyn/cm), which is the force per unit length. Pascal and N/m are SI units, not cgs units.

The speed of sound in water at 20 °C is approximately 1474 m/s, which is the most accurate value among the given options. Other values are either approximate or less precise.

Francis William Aston invented the mass spectrograph, which allowed the measurement of isotopic masses and led to the discovery of isotopes. This invention was a significant advancement in mass spectrometry.

A definite area or space where a thermodynamic process takes place is called a thermodynamic system. The other options refer to different concepts: a thermodynamic cycle is a series of processes, a thermodynamic process is a change within the system, and thermodynamic laws govern these processes.

A moving object always possesses kinetic energy because kinetic energy is the energy associated with motion. Potential energy depends on position, thermal energy relates to heat, and magnetic energy depends on magnetic fields, so they are not always present in a moving object.

Alpha rays consist of positively charged alpha particles (helium nuclei), making them positively charged particles emitted by radioactive elements. Beta rays are negatively charged electrons, and gamma rays are neutral electromagnetic radiation.

The antiparticle of an electron is called a positron, which has the same mass as an electron but a positive charge. This makes option A the correct answer.

A dioptre is a unit of measurement for the optical power of a lens or curved mirror, defined as the reciprocal of the focal length measured in meters. It is not related to luminous intensity, general power, or astronomical distances.

Communication satellites are typically placed in geostationary orbit, which is a specific type of geosynchronous orbit where the satellite remains fixed over one point on the Earth's equator, making option C correct. Geosynchronous orbit (option A) is a broader category that includes geostationary but also other orbits with the same period as Earth's rotation but different inclinations or eccentricities. Semi synchronous orbits (option B) are used for other purposes like GPS satellites, not communication satellites.

When a bullet penetrates a target, the kinetic energy of the bullet is converted primarily into mechanical energy, which causes deformation and damage to the target. However, a significant portion of the kinetic energy is also converted into heat energy due to friction and impact. Therefore, both mechanical energy and heat energy are produced during the penetration process, making option C ('Both B&D') the most accurate answer.