Mobile communication is used to communicate with others in different locations without the use of any physical connection like wires or cables.

Sky appears blue :
when white light from the sun enters the earth's atmosphere scattering takes place.
According to Ray light's scattering
\(\text { Law, } \operatorname{S\alpha } \frac{1}{\lambda_{4}}\)

de Broglie wavelength \(\lambda=\frac{\mathrm{h}}{\mathrm{mv}}\)
Kinetic energy of electron K \(=\frac{1}{2} m v^{2} \text { (or) } v=\sqrt{\frac{2 K}{m}}\)
Now de Broglie wavelength is \(\lambda=\frac{h}{m v}=\frac{h}{m \sqrt{2 K / m}} \)
\(\lambda=\frac{h}{\sqrt{2 m K}} \)

The minimum energy needed for an electron to escape from the metal surface is called work function of that metal.
Unit: electron volt (eV).

(i) To move the hole in a given direction, the valence electrons move in the opposite direction.
(ii) Electrons flow in a N-type semiconductor is similar to electrons moving in a metallic wire.
(iii) The N- type dopant atoms will yield electrons available for conduction.

(i) α - decay :
\(_{ Z }^{ A }{ X\rightarrow }_{ Z-2 }^{ A-4 }{ Y+ }_{ 2 }^{ 4 }{ He }\) 
(ii) β^- decay :
\(_{ Z }^{ A }{ X\rightarrow }_{ Z+1 }^{ A }{ Y+ }{ e }^{ - }+\overset { - }{ v } \)
(iii) β⁺ decay :
\({ }_{\mathrm{Z}}^{\mathrm{A}} \mathrm{X} \rightarrow{ }_{\mathrm{Z}-1}^{\mathrm{A}} \mathrm{Y}+\mathrm{e}^{+}+\mathrm{v} \)
(iv) Gamma emission :
\({ }_{\mathrm{Z}}^{\mathrm{A}} \mathrm{X}^{*} \rightarrow{ }_{\mathrm{z}}^{\mathrm{A}} \mathrm{X}+\gamma \text { ray } \)

General Notation -\(_{ Z }^{ A }{ X }\)
A - Mass number of nucleus - the total number of neutrons and protons in the nucleus
Z - atomic number of nucleus - the total number of protons in the nucleus
X - chemical symbol of the element.

(i) If the scattering of light is by atoms and molecules which have size a very less than that of the wavelength λ of light a <.
(ii) The intensity of Rayleigh's scattering is inversely proportional to the fourth power of wavelength.
\(1\propto \cfrac { 1 }{ { \lambda }^{ 4 } } \)

The principle of reversibility states that light will follow exactly the same path if its direction of travel is reversed.

One ampere is defined as that constant current when it is passed through each of the two infinitely long parallel straight conductors kept side by side parallely at a distance of one meter apart in vacuum causes each conductor to experience a force of 2 x 10^-7 newton per meter length of conductor.

When an electric current passing through a coil changes with time, an emf is induced in the neighboring coil. This phenomenon is known as mutual induction.

Coulomb's law \(\overrightarrow{F_{21}}=\frac{k q_{1} q_{2}}{r^{2}} \hat{r}_{12}\)
where, q₁ - charge; q₂ - charge
r - distance between the charges
\(\hat{r}_{12}\)- the unit vector directed from charge q₁ to charge q₂
k = Proportionality constant

A superconductor is any material that can conduct electricity with no resistance. In most cases, materials such as metallic elements or compounds offer some resistance at room temperature, but offer less resistance at a temperature known as its critical temperature.

The angle of incidence at which a beam of unpolarised light falling on a transparent surface is reflected as a beam of plane polarised light is called polarising angle or Brewster's angle.
When the reflected ray in plane polarised, the angle between the reflected ray (BC) and the refracted ray (BD) is 90^o angle.
Therefore, i_P + 90° + r_p = 180°
i_P = 90 - r_p.