Slideshow on Radiation detectors given to GET 2012 batch.

GET 2012 batch can download the pdf file and can make any queries on subject in the comments box below.

How does a Light Emitting diode (LED) work?


Light Emitting Diode (LED) is always operated in forward bias mode.


Direct band semiconductors are used for LEDs.

Before applying voltage




After applying voltage



At sufficient voltage, electrons gain sufficient voltage so that they combine with holes to give light which has color that depends on energy gap of chosen semiconductor.

The wavelength of emitted light depends on energy gap and is expressed as 1.24 / Eg; where Eg is energy gap.


Equivalent circuit of a capacitor

The equivalent circuit of an actual capacitor shown below indicates that there are other characteristics besides capacitance to be considered.

i) Inductance (L) of the leads and plates
ii) Resistance (R1) of dielectric (leakage resistance)
iii) Resistance (R2) of leads and plates (effective series resistance)
iv) C is measured capacitance





Is there energy associated with intrinsic inertia, the rest mass?

We could have the object at rest to annihilate with an "anti-object", producing radiation possessing energy.
So, yes, there is energy associated with the rest mass.

while creating an atom, various particles like electrons, protons, neutrons are to be brought in together. Every bit of energy that goes into creating the object would be accompanied by an increase in inertia.

According to relation E = ΜC^2

The following figure sketches this symbolically. Starting from zero for both the object's energy and its inertia and adding up increments, we emerge with E=MC^2.



The attribute energy is always accompanied by attribute inertia.

In 1905, Einstein summarized his theoretical discovery with the sentence,

" The mass [i.e inertia] of a body is a measure of its energy content."

Energy , in all forms has property of inertia, the reluctance to undergo a change in velocity. The more energy that went into forming a body, the more inertia the body has.