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Numerical from Electrostatics

Three point charged lie along the x axis in a vacuum: charge 1 in the middle, with charge 2 to the left, and charge 3 to the right. The magnitude of charge 1 is +3 microcoulomb, the magnitude of charge 2 is -4 microcoulomb, and the magnitude of charge 3 is -7 microcoulomb. The distance between charges 1 and 2 is 20 cm, while the distance between charges 1 and 3 is 15 cm. Determine the magnitude and direction of the net electrostatic force on charge 1.

Asked Tammy

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

Capacitance, voltage and Potential difference

the capacity of parallel plate condenser is 5 micro Faraday. When a glass plate is placed between the plates of the conductor  its potential become 1/8th of the original value. The value of dielectric constant will be
(A)1.6
(B)5
(C)8
(D)40

 

Answer:

The charge remains same

Use Cm=KCo
and
V reduced to 1/8 means capacitance increased 8 times since Q=CV
So, the answer is evident

Why there is a 4(pi) in Coulomb’s law?

Why there is a 4π in Coulomb’s law?

Asked Rick Ghosh

Answer:

This is a consequence of geometry.

Please remember that Coulomb’s law is stated originally for point charges  at rest. By symmetry, a point charge should exert equal force on a test charge at all points equidistant from it, which constitute a spherical shell of surface area 4πr2.

This consideration itself suggests the inverse square relation ship as well as the need for 4π.

That was actually my explanation for it.

The term 4π was not there when Coulomb’s law was first stated in cgs system. The term 4π was introduced in SI on rationalization of units based on Maxwell’s equations of electromagnetism.

But I feel that  my earlier explanation is simple and convincing.

Hope you got it.

Further discussions are welcome.

Size of a soap bubble when charged

What will happen to the size of the soap bubble if the bubble is given charges ?

Asked VARSHA UDAYAKUMAR

Answer: When a soap bubble is charged, its size increases.

Under normal condictions, a soap bubble is in equilibrium un der two opposing forces – the force of surface tension which tries to compress it and the force due to excess pressure which tries to expand it.

When charged, the force of repulsion among the like charges will try to expand the soap bubble further resulting in an increase in size of the bubble.

How does a microwave oven work?

Now, microwave oven is so popular that majority of houses have one. Many use it mainly to reheat food without loss of nutrient. The advantage is that the microwave heats up the food very fast.

Some observations made on microwave oven are,

  • It does not heat up the vessels directly
  • It is not able to cook food contained inside metal vessels
  • If the turn table does not work, cooking will not be even.

 

So, it is pertinent to ask how the mechanism of heating in a microwave oven is different from other heating devices?

Here the water molecules, which are polar in nature play the magic. (A polar molecule is one in which the centre of mass of positive charges and the centre of mass of negative charges do not coincide and have a net dipole moment.) When microwaves are passed through food materials, the water molecules contained in them tends to turn and this rapid churning of water molecules develops a lot of heat. The turn-table adds to the churning and randomization developing heat more rapidly.

The food materials contained in a closed metal vessel will not be heated up by the microwave oven as they do not allow microwaves to pass through them. The metals are opaque to microwaves.

Why the food materials heated using microwave dry up and become stiff when cool?

In a microwave oven, the water molecules are heated very fats that the water is converted readily into steam. If kept open, the steam will escape and the material will become hard when cooled due to the decrease in the water content.

What are the limitations of Van de Graff generator?

What are the limitations of Van de Graff Generator?

Saikat asked

Answer:

One of the limitations of Van de Graff generator is the potential to which the dome can be raised. In normal condition, discharge takes place when the potential reaches 3 x 106 V. The potential can be increased further by  placing the entire system in a container filled with high-pressure gas.

(Are there more? Visitors are requested to post as comments)

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