Physics

Electric current in a solid metal conductor is caused by the movement of electrons, which are free to move through the metal lattice. Protons, metal atoms, and metal ions do not move freely in a solid conductor to create current.

When a lift accelerates upward, the normal force exerted by the floor on the body increases, making the apparent weight greater than the true weight (which is due to gravity alone).

Concave lenses are used to correct myopia (nearsightedness). In myopia, the image of distant objects is focused in front of the retina, causing distant objects to appear blurry. Therefore, if a person wears concave lenses, it means that normally (without glasses), the image of distant objects is focused in front of the retina, not behind it.

The Greeks are considered pioneers of physics because early Greek philosophers like Aristotle and Archimedes laid foundational concepts in natural philosophy, which evolved into modern physics.

Cadmium is used in control rods because it is an excellent neutron absorber, which helps regulate the nuclear fission reaction by controlling the number of free neutrons. Graphite and heavy water act as moderators, not control rod materials. Therefore, cadmium is the correct choice for control rods.

Vernier calipers are suitable for measuring internal diameters, such as that of a test tube, because they have jaws designed to measure inside dimensions accurately. Screw gauges are typically used for measuring small external dimensions, and bore gauges are specialized tools not commonly used for test tubes.

The acceleration due to gravity on a planet depends on its mass and radius. According to NASA's planetary data, Mercury's surface gravity is approximately 3.70 m/s², which is slightly less than Mars' surface gravity of about 3.71 m/s². Jupiter and Neptune have much higher surface gravities (about 24.79 m/s² and 11.15 m/s² respectively) due to their larger masses. Therefore, among the given options, Mercury has the minimum acceleration due to gravity.

A photostat machine works on the principle of electrostatic image making, where an electrostatic charge is used to create an image on a photoconductive surface, which is then transferred to paper.

Time is a fundamental (base) quantity in physics, not derived from other quantities. Density, volume, and area are all derived quantities calculated from base quantities such as mass, length, and time.

The universal gas constant R is accurately given as 8.314 J/(mol·K), which is the standard value used in physics and chemistry for calculations involving ideal gases.

The average translational kinetic energy per molecule of an ideal gas is given by (3/2)kT, where k is the Boltzmann constant. Since R = N_a k (R is the gas constant and N_a is Avogadro's number), the expression can be written as (3RT)/(2N_a), which corresponds to option C.

The force transmitted through a string, rope, or cable when it is pulled tight is called tension. It acts along the length of the string and pulls equally on the objects at both ends.

A bird on a high tension wire does not get electrocuted because its body does not provide a closed circuit for current to flow through to the ground. Without a potential difference across its body, current does not pass through it.

In an isentropic process, which is both adiabatic and reversible, no heat is exchanged with the surroundings, so all the work done comes from the internal energy change. Thus, effectively, all the supplied energy is converted into work. In contrast, isothermal, isochoric, and isobaric processes involve heat exchange without full conversion to work.

The electrostatic force between two elementary charged particles such as electrons is approximately 10^36 times stronger than the gravitational force between them at the same distance. This is a well-known fact in physics, reflecting the relative strengths of the fundamental forces. Therefore, the correct answer is option B (10^36). The originally given correct answer (C, 10^12) is incorrect, and the explanation in the question also supports 10^36 as the correct ratio.

In the CGS (centimeter-gram-second) system, the unit of force is the dyne. One dyne is the force required to accelerate a mass of one gram at a rate of one centimeter per second squared. Newton is the SI unit of force, erg is a unit of energy in CGS, and joule is the SI unit of energy.

The least count of a Vernier caliper is calculated as the difference between one main scale division (MSD) and one Vernier scale division (VSD). Typically, 10 Vernier scale divisions coincide with 9 main scale divisions. If one main scale division is 1 mm, then one Vernier scale division is 0.9 mm. Therefore, the least count = 1 mm - 0.9 mm = 0.1 mm. Hence, the correct least count is 0.1 mm, which corresponds to option C.

The prefix 'Mega' in the metric system is represented by the symbol 'M', which denotes a factor of 10^6. Therefore, option C is correct.

The triple point of water is a well-defined thermodynamic state where water coexists in solid, liquid, and vapor phases in equilibrium. According to authoritative sources including the National Institute of Standards and Technology (NIST) and scientific literature, the triple point of water occurs at a temperature of exactly 273.16 K (which is equivalent to 0.01 °C) and a pressure of approximately 611.657 Pa (about 0.611 kPa). Option C correctly states the temperature as 273.16 °C (which is a typographical error in the unit; it should be 273.16 K) and the pressure as 0.611 kPa, which matches the standard pressure value. Option D has the correct temperature unit (Kelvin) but an incorrect pressure value (750 kPa is far too high). Therefore, option C is the most accurate choice given the options, with the note that the temperature unit should be Kelvin, not Celsius. The triple point temperature is defined as 273.16 K, not °C.

When a ball is thrown upwards and bounces back, the directions of displacement, velocity, and acceleration all change during the motion. Displacement changes as the ball moves up and then down, velocity changes direction at the peak, and acceleration due to gravity always acts downward, so its direction relative to velocity changes as well.

When two identical conducting spheres are connected by a wire, charges redistribute equally. Initially, charges are +2Q and -Q, total charge is +Q. After connection, each sphere has charge +Q/2. The force depends on the product of charges, so new force F' = k*(Q/2)*(Q/2)/r^2 = k*Q^2/4r^2, which is one-fourth the original force F. Hence, the force becomes F/4.

Gamma rays are electromagnetic radiation and have no charge, so they are not deflected by electric or magnetic fields. Alpha and beta rays are charged particles and are deflected accordingly.

In semiconductors, electrical conductivity increases with temperature because more charge carriers are generated as temperature rises. In contrast, conductors typically show decreased conductivity with increasing temperature due to increased lattice vibrations.

The mass-energy relation, expressed as E=mc², is a direct consequence of Einstein's Special Theory of Relativity, which relates mass and energy as interchangeable.

Historically, atoms were considered the smallest indivisible particles of matter, but modern physics has shown that atoms are divisible into smaller particles: electrons, protons, and neutrons. Protons and neutrons themselves are made of quarks. The truly indivisible particles known today are elementary particles such as quarks, leptons (including electrons), and gauge bosons, which are fundamental constituents of matter according to the Standard Model. Therefore, the atom is not the smallest indivisible particle, making option D ('None of these') the correct answer.