Physics

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.

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.

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.

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.

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).

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.

A petrol engine is a Spark Ignition (SI) engine because it ignites the air-fuel mixture using a spark plug. It is not a Compression Ignition (CI) engine, which is typical for diesel engines. While it is an Internal Combustion (IC) engine, the most specific and correct classification here is SI engine.

The velocity of sound in a gas at constant temperature depends primarily on the temperature and the properties of the gas, not on the pressure or atmospheric level. Since the temperature is assumed constant, the velocity of sound at 4 atmospheres is the same as at 1 atmosphere, making the ratio 1:1.

The SI unit with the symbol 'cd' is the candela, which measures luminous intensity. Other options like Cm (centimeter), Ampere (A), and Second (s) have different symbols and represent different quantities.

Energy is defined as the capacity to do work. This is a fundamental concept in physics distinguishing energy from work, power, and momentum.