Physics

A wattmeter is specifically designed to measure the power in an electric circuit, which is the rate at which electrical energy is consumed or produced. The other instruments listed measure different quantities: a wavemeter measures frequency, and a viscometer measures viscosity.

A dioptre is the unit of measurement for the optical power of a lens, which is the reciprocal of its focal length measured in meters. Therefore, it directly relates to focal length, not the lens itself as a general object.

The M.K.S. system (Meter-Kilogram-Second) was introduced by Giovanni Giorgi, who proposed this system as a practical set of units for scientific measurements. The other options are unrelated to the introduction of the M.K.S. system.

A convex mirror always forms a virtual, diminished, and upright image regardless of the object's position. It never forms a real or inverted image, and the image is smaller rather than larger.

The distance between the optical center of a convex lens and its principal focus is defined as the focal length. This is a fundamental property of lenses that determines their converging power.

A hydrogen bomb operates on the principle of nuclear fusion, where light atomic nuclei combine to form heavier nuclei, releasing enormous energy. This distinguishes it from atomic bombs, which rely on nuclear fission.

The speed of sound in air at room temperature (around 20 °C or 68 °F) is approximately 343 meters per second, which converts to about 767 miles per hour. The given options are 1257 mph, 755 mph, 330 mph, and None of these. Since 330 mph is significantly lower than the actual speed and 755 mph is close but still slightly off, the best accurate choice is "None of these". Therefore, option D is correct. The original explanation was incorrect because it confused meters per second with miles per hour and gave an inaccurate conversion.

When sound waves pass from air to water, their frequency remains unchanged because frequency depends on the source of the sound and does not change when the medium changes. However, speed and wavelength change due to different properties of the media, and intensity can also vary due to absorption and reflection.

Magnetism is a force that can attract or repel magnetic materials. Heat and light are forms of energy, and 'Kinetic' is an adjective related to motion, not a force itself.

Materials whose atoms can be split are called fissionable materials because they can undergo nuclear fission, where the nucleus splits into smaller parts. Fusionable refers to materials that can undergo fusion, combustible relates to burning, and 'None of these' is incorrect.