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# Tag Archives: Voltage

## Transformers

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.

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)

## V proportional to I or I proportional to V in Ohm’s Law?

Why we used I proportional to V?
Can we write V proportional to I also?

Both are ok. If we are changing the current and observing the voltage, then it is V∝ I

If we are changing the voltage and observing the current, then

I∝ V

In general, we write

the dependent variable proportional to the independent variable

dependent variable  = the quantity measured by us

independent variable = the quantity fixed by us

## Current Carriers and conduction

1. Do the protons flow when current flow?
2. In case of semiconductor do the holes flow?

In metallic conductors, free electrons are the current carriers, i.e, it is due to the motion of the free electrons that conduction takes place in a metallic conductor. The protons do not move as they are inside the nucleus and bound by strong nuclear forces. It is the electrons of the outermost shell of the atom which are least bound to the atom, flow and cause conduction

In semiconductors the current carriers are free electrons and holes.

What are holes?

Holes are actually vacancies created when an electron is freed from a bond. It is assigned a positive charge. When a potential difference is applied across a semiconductor, the free electrons move towards the positive terminal as in the case of a metal. The bonded electrons also move towards positive terminal from vacancy to vacancy and this causes the holes  t move towards the negative terminal.

## A Numerical problem from electricity

In the given diagram,the cell and the ammeter, both have negligible resistance. the resisitors are identical. With switch K open , the ammeter reads 0.6 A. What will be the ammeter reading when the switch is closed?

When the switch is open, the effective resistance is R/2, since the two resistances R each are in parallel.

Therefore, the pd, V = I x R/2 = 0.6 x R/2 = 0.3 R

When the key is closed, the effective resistance becomes R/3

Now the reading of the ammeter, I’ = V/(R/3) = 0.3R/(R/3)=0.9A

## Work done in accelerating a proton

The mass of a proton is 1840 times that of an electron. it is accelerated to a potential difference of 1kV. find the amount of work done in process. (Ujjwal Sharma asked)

The work done = the KE acquired = eV=1.6 x 10-19 x 1000 = 1.6 x 10-16 J

## Difference between Dielectric Break Down and Corona Discharge

HOW IS CORONA DISCHARGE DIFFERENT FROM DIELECTRIC BREAKDOWN IN THE CASE OF VANDEGRAFF GENERATOR

• Corona (egrejeen.wordpress.com)

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