Units and Measurement

Conductance is the reciprocal of resistance, measured in siemens (S). The traditional unit is 'mho' (ohm spelled backward), which equals one siemens. Options A and B are incorrect units related to resistance (ohm) and resistivity (ohm/m). Option D incorrectly adds a per-meter dimension.

The SI unit of force is the newton (symbol: N), named after Sir Isaac Newton. One newton is defined as the force required to accelerate a mass of one kilogram at one meter per second squared (1 N = 1 kg·m/s²). Pascal is the SI unit of pressure, not force.

The SI unit of power is the watt (symbol: W), named after James Watt. One watt equals one joule per second (1 W = 1 J/s). Newton is the unit of force, pascal is pressure, and joule is energy/work. Power is the rate at which work is done or energy is transferred.

The SI unit of magnetic flux density is the Tesla (T). Gauss and Oersted are CGS units for magnetic field and magnetic field intensity respectively. Weber is the SI unit for magnetic flux, not flux density.

Watt is the SI unit of power, defined as one joule per second. Joule is the unit of energy or work, Newton measures force, and Ampere measures electric current. Power is the rate of energy transfer.

Newton is defined as the force required to accelerate 1 kilogram at 1 m/s² in the direction of applied force. By dimensional analysis: F = ma, so [N] = [M][L][T]⁻² = kg·m/s². Option A correctly shows this.

The kilogram (kg) is the SI base unit for mass. It is defined by taking the Planck constant h as exactly 6.62607015 × 10^-34 joule-seconds. Previously, it was defined as the mass of a platinum-iridium cylinder kept in France.

The metre (m) is the SI base unit for length. Since 1983, it has been defined as the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second. This definition provides an exact, unchanging standard.

The ampere (A) is the SI base unit for electric current. Since 2019, it is defined by taking the elementary charge e as exactly 1.602176634 × 10^-19 coulombs. Current is defined as the flow of electric charge per unit time.

Kelvin (K) is the SI base unit for thermodynamic temperature. It is named after William Thomson, Lord Kelvin. Celsius and Fahrenheit are other temperature scales but Kelvin is the standard SI unit.

Candela (cd) is the SI base unit for luminous intensity - the power of light emitted in a particular direction. It measures how bright a light source appears to the human eye.

Mole (mol) is the SI base unit for amount of substance. It measures the number of particles (atoms, molecules, ions) in a sample. One mole contains approximately 6.022 × 10^23 particles (Avogadro's number).

Joule is the SI derived unit for energy, work, and heat. It is defined as the energy transferred when a force of one newton acts over a distance of one meter. Watt measures power (energy per time), not energy itself.

Power is the rate at which energy is transferred or work is done, and its SI unit is the watt (W). One watt equals one joule per second. Joule is the unit of energy, mole measures amount of substance, and volt measures electric potential.

Voltage, also called electric potential difference, has the SI unit of volt (V). Kelvin is for temperature, joule for energy, and mole for amount of substance. The volt is named after Alessandro Volta, the inventor of the electric battery.