Units and Measurement

Lux is the SI unit of illuminance, which measures luminous flux (light power perceived by human eye) per unit area. It is distinct from luminous intensity (candela) or luminous flux (lumen). Illuminance describes how much light falls on a surface.

Amps (amperes) are the base electrical units for measuring electric current - the flow of electric charge. Hertz measures frequency, ergs are units of energy/work, and 'waves' is not an electrical unit. The question asks specifically about electrical units, and current measurement is fundamental to electrical engineering and physics.

Amps (amperes) are the SI unit for electric current, measuring the flow of electric charge. Hertz measures frequency, ergs are a CGS unit of energy, and 'waves' is not a measurement unit at all.

Power can be measured in both Watts (the SI unit) and Horse Power (a non-SI unit still widely used, especially for engines and vehicles). 1 horsepower ≈ 746 watts. Pascal measures pressure, and Lambert measures luminous intensity or brightness. Both B and D are correct for this MC-2 question.

Gauss is the unit of magnetic induction (also called magnetic flux density) in the CGS system. It measures the strength of a magnetic field. Electric flux is measured in units like Maxwell or Weber·m², stellar distance in parsecs or light-years, and luminous intensity in candela. Only option A is correct.

Energy density measures energy per unit volume, making joule per cubic metre (J/m³) the correct SI unit for volumetric energy density. Joule per mole is molar energy, joule per kilogram is specific energy (per mass), and watt is power (rate of energy transfer).

Mass density is defined as mass per unit volume, making kilogram per cubic metre (kg/m³) the correct SI unit. Cubic metre is volume alone, square metre per second is kinematic viscosity, and metre per second cubed is not a standard physical quantity.

Thermal conductivity (k) measures a material's ability to conduct heat. Its SI unit is W/mK (Watts per meter-Kelvin), which represents heat transfer rate per unit length per unit temperature difference.

Power is the rate of doing work or transferring energy, measured in joules per second (J/s). This is equivalent to the watt (W), the SI unit of power. Since 1 watt = 1 joule/second, the statement is correct.

Impedance (Z) is the total opposition to alternating current in an electrical circuit, measured in ohms (Ω). Newton (N) is force, joule (J) is energy, and coulomb is electric charge.

Wave number (k) is the spatial frequency of a wave, defined as the number of wavelengths per unit distance, measured in reciprocal meters (m⁻¹). 'm²' is area, 'm' is length, and 'm/s' is speed or velocity.