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Q.2. Sunil and his parents were travelling to their village in their car. On the way his mother noticed some grey coloured panels installed on the roof of a low building. She enquired from Sunil what those panels were and Sunil told his mother that those were solar panels.
(a) What were the values displayed by Sunil and his mother? State one value for each.
(b) In what way would the use of solar panels prove to be very useful?
(c) Name the semiconductor device used in solar panels. Briefly explain with the help of a diagram, how this device works.

$$\begin{gathered} a. sunil mother is curious to know new things and good observer. \\ sunil have good knowledge of renewable sources of energy. \\ b. they can be used for generation of electrcity. \\ its clean energy \\ at high scale we can used to use heavy appliance. \\ can be used for street light. \\ c. pn junction diode is used in solar panels . they are special diode having photo sen\sin g pwer. \\ Photocells are devices that transfer light energy directly into electrical energy. They produce DC - direct current - electricity. This is electricity in which the current moves in the same direction all the time. Photocells have no moving parts, and can work in remote locations. \end{gathered}$$
Well, it works due to the photo-electric effect : the conversion of an EM-wave (light) into an electric current. It is this phenomenon that Einstein explained in terms of quantized energy It also suggested for the first time that EM-waves could be seen as a stream of particles called photons. Einstein did not invent the name photons and i must say that this effect did NOT prove the particle-behaviour of waves, it just suggests it. This is a common misconception. The incident light knocks lose conduction electrons from the target electrode. This electron will have enough energy to move to the surface of the electrode and it will then be 'ejected from' that electrode, yielding an electric current. The conduction electrons are bound to the constituting atoms of the electrode with less energy, so it is easier to knock them lose. These electrons are the valence (ie the outer electrons) electrons of the constituting atoms. When you put many atoms together, their wavefunctions (more specifically, their orbitals) will overlap and this yields a 'continuous' region over the atom-lattice, that can be occupied by these electrons. they are not localized to one atom but they can move 'freely' over the entire atomic-lattice. 
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