In metals, the electrons in the outer most shells are loosely bound to the nucleus. Even at room temperature, these large number of electrons which are moving inside the metal in random manner and they cannot leave the surface of metal. So that metals have a large number of free electrons.

Robots are automated machines which have many mechanical parts like wheels, arms, fingers, legs etc. Therefore a strong material is needed. For a given size, steel has several times stronger.

(i) The output signal is reversed by 180^o. During the positive half cycle, Input signal (V_s) increases the forward voltage across the emitter-base.
(ii) As a resultthe base current (I_B) increases. Consequently, the collector current (I_C) increases ß times. 
(iii) This increases the voltage drop across R_c (I_C R_C) which in turn decreases the collector-emitter voltage (V_CE).
(iv) Therefore, the input signal in the positive direction produces an amplified signal in the negative direction at the output.

RADAR stands for RAdio Detection And Ranging.

(i) Near point focusing:
The eye is least strained when image is formed at near point, i.e. 25 cm. The near point is also called as least distance of distinct vision.
(ii) Normal focusing:
The eye is most relaxed when the image is formed at infinity. The focusing is called normal focusing when the image is formed at infinity.

The phenomenon of spontaneous emission of highly penetrating radiations such as α, β and ⋎ rays by an element is called radioactivity and the substances which emit these radiations are called radioactive elements.

(i) During sunrise and sunset, the light from sun travels a greater distance through the atmosphere.
(ii) Hence, the blue light which has shorter wavelength is scattered away and the less scattered red light of longer wavelength manages to reach our eye.
(iii) This is the reason for the reddish appearance of sky during sunrise and sunset.

The angle between the incident ray and deviated ray of light ray is called Angle of deviation due to reflection. d = 180 - 2i

\(\cfrac { sini }{ sinr } =\cfrac { { n }_{ 1 } }{ { n }_{ 2 } } \) (Snell's law)
The term \(\left( \cfrac { { n }_{ 2 } }{ { n }_{ 1 } } \right) \) is called relative refractive index of second medium with respect to the first medium \(n_{21}=\left( \cfrac { { n }_{ 2 } }{ { n }_{ 1 } } \right) \)
(i) Inverse rule: \(n_{21}=\frac{1}{n_{21}}(or)\cfrac { { n }_{ 1 } }{ { n }_{ 2 } }=\frac{1}{(n_2/n_1)}\)
(ii) Chain rule: \(n_{32}=n_{31} \times n_{21}(or)\frac{n_3}{n_2}=\frac{n_3}{n_1}\times\frac{n_1}{n_2}\)

Magnetic dipote moment \(\vec { p }_{ m } \) is defined as the product of its pole strength and magnetic length. It is a vector quantity denoted by \(\vec { p }_{ m } \)
\(\vec { p }_{ m } ={ q }_{ m }\vec { d } \)

Q factor is defined as the ratio of voltage across L or C to resonance to the applied voltage
Q - factor = \(\frac{Voltage \ across \ L \ or \ C \ resonance }{Applied \ voltage}\)
\(Q-factor=\frac{X_{L}}{R}=\frac{1}{R}\sqrt\frac{{L}}{C}\)

First law:
Whenever magnetic flux linked with a closed circuit changes, an emf is induced in the circuit. Which lasts in the circuit as long as the magnetic flux is changing.
Second law:
The magnitude of induced emf in a closed circuit is equal to the time rate of change of magnetic flux linked with the circuit.

The energy crossing per unit area per unit time and perpendicular to the direction of propagation of the electromagnetic wave is called the intensity.
Intensity, I = [u] c or \(I=\frac { total\ electromagnetic\ energy(U) }{ Surface\ area(A)\times time(t) } \)
\(=\frac { Power(P) }{ Surfacearea(A) } \) 

The number of electric field lines crossing a given area kept normal to the electric field lines is called electric flux.

It there are more than two charges, the total force acting on a given charge is equal to the vector sum of forces exerted on it by all the other charges.
Consider a system of n charges namely q₁, q₂, q₃ ...q_n. The force on q₁ exerted by the charge q₂ is \(\overrightarrow{F_{12}}=k \frac{q_{1} q_{2}}{r_{21}^{2}} \hat{r}_{21}\) .
The force on q₁ exerted by the charge q₃ is \(\overrightarrow{F_{13}}=k \frac{q_{1} q_{3}}{r_{31}^{2}} \hat{r}_{31}\)
By continuing this, the total force acting on the charge q₁ due to all other charges is given by
\( \vec{F}_{1}^{\text { tot }}=\overrightarrow{F_{12}}+\overrightarrow{F_{13}}+\overrightarrow{F_{14}}+\ldots+\vec{F}_{1 n} \)
\(\vec{F}_{1} ^{\text { tot }}=k\left\{\frac{q_{1} q_{2}}{r_{21}^{2}} \hat{r}_{21}+\frac{q_{1} q_{3}}{r_{31}^{2}} \hat{r}_{31}+\frac{q_{1} q_{4}}{r_{41}^{2}} \hat{r}_{41}+\ldots+\frac{q_{1} q_{n}}{r_{n 1}^{2}} \hat{r}_{n 1}\right\}\) 

The internal resistance of a cell is the resistance offered to the flow of current (by the electrolyte) inside the cell.

Macroscopic form of Ohm's law is V = IR
Where V - Potential difference
I - current 
R - resistance of a conductor.

(i) The electron in an atom moves around nucleus in circular orbits under the influence of Coulomb electrostatic force of attraction. This Coulomb force gives necessary centripetal force for the electron to undergo circular motion.
(ii) Electrons in an atom revolve around the nucleus only in certain discrete orbits called stationary orbits where it does not radiate electromagnetic energy. Only those discrete orbits allowed are stable orbits.
(iii) The angular momentum of the electron in these stationary orbits are quantized (ie) L = \(\frac{nh}{2\pi}\) This is known as Bohr quantization condition.
(iv) The energy of the orbits are not continuous but only discrete. This is called quantization of energy.
(v) An electron can jump from one orbit to another orbit by absorbing or emitting a photon whose energy is equal to the difference in energy between the two orbital levels.