## What is the Internal Resistance of the cell ?

Ans:  The opposition offered by the electrolyte of the cell to the flow of electric current through it is called internal resistance of the cell. It is denoted by ‘ r ‘

Internal Resistance depends on

(1)  Distance between electrodes (r ∝ d)

(2)  Area of electrodes ( dipped in electrolyte) (r ∝ 1/A)

(3)  Temperature of electrolyte.

## Why does the mass of a body change when it emit or absorb photons ?

♦Scientific Reasoning : Why does the mass of a body change when it emit or absorb photons ?♦
Ans. As photon has energy hν and according to theory of relativity, energy E is equivalent to a mass (E/c²), so photon has a mass (hν/c²). So theoretically the mass of a body will decrease if it emits photons and will increase if it absorbs them. However due to small value of h =(6.6 x 10-34 Js) and large value of c( = 3 × 108 m./s) as the mass of an optical photon is too small, the change in mass of a body due to emission or absorption of photons is practically negligible as compared to the mass of the body.

## What is the Electromagnetic Waves ?

Ans: Electromagnetic waves are those waves in which there is a sinusoidal variation of electric and magnetic field vectors at right angles to each other as well as at right angles to the direction of propagation of waves. In electromagnetic waves, both the field vectors  vary with time and space and have the same frequency and same phase.

## How does Modem work ?

Ans: We know that computers operate in the digital world, but telephone lines require a different method of transmission. The modem modulates the digital signal into a sine wave. This can be broadcast over a telephone line. The signal is transmitted over the line, until it reaches the IP hub. At this point, the sine wave is demodulated into a digital signal once more, and the connection with the internet is complete. Modems can perform this work at a variety of speeds, depending on the technology and availability of access lines.

## Why the name Transistor ?

Ans: By forward biasing input junction (emitter-base junction) and reverse biasing output junction (collector-base junction), a low resistance of forward biased junction can be transformed into a high resistance of reverse biased junction.

Also by interchanging biases, a high resistance can be transformed into a low resistance. Hence the junction triode is called TRANsformer of reSISTOR, which in short becomes TRANSISTOR.