What are the differences between Plane angle and solid angle?

1. System of Units:

(i) CGS, MKS and SI units are metric systems of units whereas FPS is a British system of units.

(ii) The quantities which cannot be expressed in terms of any other physical quantities are called fundamental quantities. Length, mass, time, current, temperature, amount of substance and luminous intensity are fundamental quantities.  

2. Temperature:

(i) Temperature is the average kinetic energy of a particles in a system and its SI unit is kelvin ($K$).

(ii) In thermometers, the melting point of ice is taken as Lower Fixed Point (LFP) and boiling point of water is taken as Upper Fixed Point (UFP). 

(iii) The general formula for conversion of scales of temperature is given as, $\frac{\mathrm{C}-0}{100}=\frac{\mathrm{F}-32}{180}=\frac{\mathrm{K}-273}{100}$

3. Current:

The rate of flow of electric charge is termed as electric current and its SI unit is ampere ($\mathrm{A}$).

4.  Amount of Substance:

(i) The amount of substance is a measure of the number of entities (atoms/ molecules/ ions/ electrons/protons) present in a substance. Its SI unit is mol. 

(ii) The mol is defined as the amount of substance, which contains $6.023\times {10}^{23}$ (Avogadro Number) entities.

5. Luminous Intensity:

The amount of light emitted by a light source in a particular direction per unit time is known as Luminous intensity. Its SI unit is candela ($\mathrm{Cd}$).

6. Plane and Solid Angles:

(i) The angle between the intersection of two straight lines or intersection of two planes is known as plane angle. Its SI unit is radian ($rad$).

(ii) The angle formed by three or more planes intersecting at a common point is known as solid angle. Its SI unit is steradian ($sr$).

(iii) One steradian is defined as the solid angle at the centre of a sphere subtended by a portion whose surface area is equal to square of the radius of the sphere. 

7. Clocks and Its Working Mechanism:

(i) Quartz clock uses electronic oscillations controlled by a quartz crystal.

(ii) Atomic clock uses periodic vibrations occurring within the atom.

8. Accuracy in Measurements:

(i) Accuracy is the closeness of a measured value to the actual value.

(ii) Precision is the closeness of two or more measurement to each other.