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# Tag Archives: electron

## A question from photoelectric effect

If light of wavelength lambda is incident on metal surface, the ejected fastest electron has speed v. If the wavelength is changed to 3/4(lambda), the speed of the fastest emitted electron will be?

## Why is the force on a wire NOT carrying current is zero when kept in a magnetic field?

Explain zero force acting on a wire  which is not carrying current,on being placed inside a magnetic field.

A charge at rest will not experience any force in a magnetic field, but a moving charge will experience  a force unless it is moving parallel to the field.

In a conductor, the electrons are in rapid and random motion, but the conductor will not experience a force until a current is passing through it. (Even though the electrons are not at rest). This is because, in the absence of a current, the motion of electrons is random and there is no net drift of electrons in any direction. Thus the forces cancel out.

When a current is passed through the wire, there is a net drift and hence a net force is experienced by the current carrying conductor in a magnetic field.

Further, I want to mention that the force is experienced between the existing field and the field produced by the moving charges/ current.

## Flow of electrons and direction of current

We say current flow opposite to electron flow but what is current?

Electric current is defined as the rate of flow of charges, ie; the amount of charges flowing in 1 sec.

The direction of current was conventionally defined as the direction of flow of positive charges.
In a metallic conductor, the negatively charged particles (electrons) are moving and therefore the direction of current is taken as opposite to the direction of flow of electrons.
Hope the concept is clear.

## 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.

## 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

## Electron behaviour

Why an electron in level N when it gain energy it go to a higher energy level , why not going to a lower energy level , considering that word “higher” and “lower” refers to no of energy level but the energy of the energy level decrease as we go away from nucleus so an excited electron that gain an additional energy transfer to a higher energy level in no but lower in energy so why the electron doesn’t from its level to a lower energy level in no but higher in energy so the new energy level can bear the energy of the excited electron ?
The question is not very clear. If you can explain it further, it will be better to discuss here.

Regards,

## How atoms are formed? – Neeraj Asks

Neeraj asks: ”We have read that atoms can neither been created nor been destroyed!
I want to know from where atoms came in existence,if they can not been created,also atom contain electron and proton which are negatively and positively charged,i want to know from where these charge came?”