Understanding Physical Quantities and Their Units

This question asks us to match different physical quantities with their corresponding units. Identifying the correct units for various quantities is fundamental in physics and other sciences. Let's analyze each physical quantity given in List I and find its standard or commonly used unit from List II.

Matching Physical Quantities with Units

Let's go through each item in List I and determine its appropriate match from List II:

• A. Distance: Distance is the measure of the space between two points. While the standard international (SI) unit of distance is the metre, other units are used for specific scales. A 'Light Year' is a unit of distance used in astronomy, representing the distance light travels in one year. Therefore, Distance matches with Light Year.
• B. Amount of material: This quantity refers to the amount of substance. The SI unit for the amount of substance is the 'Mole'. One mole contains approximately $6.022 \times 10^{23}$ elementary entities (like atoms, molecules, ions, etc.). Therefore, Amount of material matches with Mole.
• C. Amount of electrical charge: Electrical charge is a fundamental property of matter. The SI unit of electric charge is the 'Coulomb'. One coulomb is defined as the amount of charge transported in one second by a constant current of one ampere. Therefore, Amount of electrical charge matches with Coulomb.
• D. Energy: Energy is the capacity to do work. The SI unit of energy is the Joule, but many other units are used depending on the context. The 'Watt Hour' is a unit of energy commonly used for measuring electrical energy consumption. It is equivalent to one watt of power expended for one hour ($1 \text{ Watt Hour} = 3600 \text{ Joules}$). Therefore, Energy matches with Watt Hour.

Based on the matching, we have:

• A matches with 3 (Light Year)
• B matches with 1 (Mole)
• C matches with 2 (Coulomb)
• D matches with 4 (Watt Hour)

So the correct code is A - 3, B - 1, C - 2, D - 4.

Revision Table: Physical Quantities and Units

Additional Information: Understanding Units

Units are essential for measuring and quantifying physical quantities. They provide a standard reference for comparison. There are base units (like metre, kilogram, second, mole, ampere, kelvin, candela in the SI system) and derived units (combinations of base units, like Newton, Joule, Coulomb, Watt). Knowing the appropriate unit for a physical quantity is crucial for solving problems and understanding physical phenomena.

Different units exist for the same quantity, often based on the scale or application. For example, distance can be measured in millimetres, metres, kilometres, inches, miles, astronomical units, or light years, depending on how far apart the points are.

It's important to distinguish between quantities that might sound similar but are different, like 'amount of material' (substance, measured in moles) and 'mass' (measured in kilograms).