Electronics

A question from semiconductors

Draw the circuit diagram used to study the characteristics of an NPN transistor in common emitter configuration.Give the shape of these characteristics & use them to define the
(i)input resistance &
(ii)the current amplification factor of the
given transistor.

Asked Vikas

Transformers

A hypothetical ideal transformer considered as a circuit element, consisting of N P turns in the primary winding, and N S in the secondary. Electrical power supplied to the primary circuit is delivered to the load in secondary circuit by means of mutual induction. The time-varying magnetic flux in the core generates an electromagnetic force over each of the windings. The voltage and current relationships are shown below. (Photo credit: Wikipedia)

Please explain what is transformer and tell what is the reason behind the working of transformer that it reduces potenial when current is high and increases potential when current is low?

Explain widely and deeply with concepts.

Answer:

Transformer is a device based on mutual inductance and is used to change the voltage of alternating (or varying) current. There are two types of transformers – stepup and stepdown.

A step-up transformer increases the voltage as the step-down transformer decreases the ac voltage.

When a transformer changes the alternating voltage, it is not adding any power, it only transforms the voltage.

As power is the product of voltage and current, as voltage increases, the current decreases. (and vice versa)

The following links will help you understand transformers in great detail.

• http://www.physlink.com/education/askexperts/ae427.cfm
• http://en.wikipedia.org/wiki/Transformer
• http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/transf.html
• http://www.nuffieldfoundation.org/practical-physics/explaining-how-transformer-works

HOW DOES A REMOTE (CONTROLLER) WORK

Explain me how infrared are detected by televison sets which are sent by remote and how does the channel change?

Asked Rahul

A remote is an electronic device which sends infra red signals whenever you press a buton on the remote controller. Each button press is translated into a sequence of 0s and 1s and accordingly the IR signal is produced.

You might have noticed the LED at the front end of the remote. The IR light cannot be seen through naked eye, but it can be seen through a mobile camera because the camera is sensitive to IR light too.
The infrared sensor of your TV receives the signal and decodes it into digital signal and sends it to the microprocessor. Appropriate actions (changing the channel, increasing the volume etc) are triggered by the microprocessor. For each operation there is a separate didital code (produced by different buttons on the remote)

Solution to HC Verma Problem

“Referring to HC Verma Part 2, chapter 29, Electric field and potential, Q 69
I think that Force is inversely proportional to square of the distance between the charged particles, so acceleration is not constant and hence
v*v  =  u*u  + 2*a*s   is not valid in this case.
How is proceed with this question ?” Satyam asked