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What are plasmons?

A plasmon is a quantum of plasma oscillation, just like photon is a quantum of light radiation.

Plasmon is a quasiparticle resulting from the quantization of plasma oscillations.

Plasmons play a large role in the optical properties of metals. Light of frequency below the plasma frequency is reflected, because the electrons in the metal screen the electric field of the light. Light of frequency above the plasma frequency is transmitted, because the electrons cannot respond fast enough to screen it. In most metals, the plasma frequency is in the ultraviolet, making them shiny (reflective) in the visible range.

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Surface plasmons

Surface plasmons are those plasmons that are confined to surfaces and that interact strongly with light resulting in a polariton

Read more at http://en.wikipedia.org/wiki/Surface_plasmon

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An interesting question from electrostatics

Two equal negative charge -q are fixed at the point (0,a) & (0,-a) on yhe y-axis. a positive charge Q is released from rest at the point (2a,0) on the x-axis. the charge Q will execute oscillatory motion how?

Asked Kritika

More questions waiting for answers:

The following questions are waiting for an answer. You can contribute your answers by the time our team answer them.

  • When a piece of paper is held with its face perpendicular to a uniform electric field the flux through it is 25.0 N·m2/C. When the paper is turned 25.0o with respect to the field the flux through it is?
  • A cylinder rests on a horizontial rotating  disc, find at what angular velocity the axes of the disc and cylinder is R and the coefficient of friction U>D/H, where D is the diameter of the cylinder and H is its height.
  • Can static friction do non zero work on an object?if yes give example . if no give reason
  • How angular momentum is different from linear momentum?

 

Sample Value based questions for Class 12 Physics

Scientific and logical reasoning is a scientific value expected from students studying Physics. Use your expertise to answer the following question.
One way to make a compass is to stick a magnetized needle into a piece of cork and float it in a glass bowl full of water. The needle will align itself with the magnetic field of the earth. Since the north pole of the needle is attracted towards the north, will the needle float towards the northern side of the bowl? Defend your answer.

 

Mr. Kishan is a farmer who was staying happily in a hut made of hey and
leafy roof. It is easy for him to renovate his home with new leaves every
year as the good quality palm leaves he get free of cost and it is
environment friendly. Most of the village people are satisfied with the
same type of huts there.
But one day during heavy lightning, many of the huts were burnt to ashes
and people were sad and disappointed. Mr. Sekhar works in electricity
department and has good knowledge of current affairs. He soon reached
the spot along with his friends and pacified them and made arrangements
for their comfortable stay. The very next day the team could erect many
lightning conductors and few cavities of metal conductors and made
awareness to the villagers about lightning and the use of things installed
there. (a) What according to you, are the values displayed by Mr. Sekhar
and his friends to help Mr. Kishan and the village people? (2)
What is the principle behind working of a lightning conductor? Also by
applying Gauss theorem show that net electric field inside the metallic
cavity is zero. (2)

 

 

 

Misconceptions on Electric Potential

We know that the potential developed at a point by a charge is the negative of the work done to bring a unit charge at that point from infinity. But how does a conducting plate develop a potential? what is the work done?

Answer:

I can smell some misconceptions in your question. It is better to revise the question after revising the topic on Elelctric Potential thoroughly.

3D Frenzy x Electric Fields

Electric potential at a point is defined as the work done per unit charge in bringing a positive test charge from infinity to that point against the electric field and without any acceleration.

When a conducting plate is charged, it is raised to some potential. Only to bring the first point charge to the plate, the work done is zero, but afterwards, repulsion is developed between the charge brought and the charge already present on the plate and therefore work is required to be done to increase the charge on the plate.

(Please revise the portions well and review the question asked)

Electric field inside and outside the plates of a capacitor

How do you find the direction of electric field on the outer or inner surface of  2 parallel plate of a capacitor ?

Answer:

 

The direction of electric field is from the positive plate to negative plate.

The electric field outside the plates is zero as the electric field due to each plate (E=Q/2ε0A) cancel out being equal in magnitude and opposite in direction.

In between the plates the two electric fields add up as they are in same direction. (From positive plate to negative plate).

The magnitude of electric field between the plates is twice the electric field due to either; i.e; E=2 x Q/2ε0A = Q/ε0A

Gauss`s law

Nagendra chowdary asked : –

“A circular ring of radius r made of a non conducting material is placed with its axis is parallel to a uniform electric field if the ring rotated by 180 degrees Does the flux changes? A Q charge is uniformly distributed on a thin spherical shell If a point charge is brought near it what is the field at the center?Is u r answer depends on whether it is conducting or non conducting?”

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