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4. a) Explain the meaning of the statement ‘electric charge of a body is quantized’.

(b) Why can one ignore quantization of electric charge when dealing with macroscopic i.e., large scale charges?

Soultion; a) Quantization of charge states that, the total charge of a body is the integral multiple of the elementary charge particle (e = 1.6 x 10-19 C)

i.e, Q = ne

b)At large scale, or for macroscopic level, system has a lot of elementary charges, so it is no more useful to calculate the total charge of that system. That’s why when we talk about the total charge on macroscopic level, we ignore quantization of charge.

5. When a glass rod is rubbed with a silk cloth, charges appear on both. A similar phenomenon is observed with many other pairs of bodies. Explain how this observation is consistent with the law of conservation of charge.

Solution; When two bodies against each other, some charge is developed on both bodies. The charges developed on the bodies are equal and opposite in nature. So, the net charge on both of the bodies is 0 and the cause behind this, an equal amount of charge repels it. When we rub a glass rod with a silk cloth, charge with opposite magnitude is generated on those bodies. This phenomenon is the simple proof of the conservation of charge.

7. a)  An electrostatic field line is a continuous curve. That is, a field line cannot have sudden breaks. Why not? (b) Explain why two field lines never cross each other at any point?

Solution; a) When a charge is paced in an electrostatic field then it experiences a continuous force. So, an electrostatic field line is a continuous curve. Since any charge can’t jump from one point to the other, it moves continuously throughout the field. So, the field line cannot have a sudden break.

b) Since tangent of the electric field lines, gives the direction of electric field. But if electric field lines intersects each other then at the point of intersection there are two different tangent would formed, or can say at same point there are two different direction of electric field, and we know it is not possible. Hence, two field lines never cross each other at any point.

14. Given figure shows tracks of three charged particles in a uniform electrostatic field. Give the signs of the three charges. Which particle has the highest charge to mass ratio?

Solution; According to fig., particle 1 & 2 are moving towards the positive charge, and from, law of charge, unlike charges attract each other, while like charges repel each other so 1 & 2 must have negative charge. And similarly for 3, it is positive charge. Now, since 3 deviate more so it has highest charge to mass ratio.

Short Questions

Q. A charge 1 is placed just outside the spherical surface. What is the electric flux through the surface?

Answer; Since there are no charge enclosed by surface, So flux through the surface is zero.

Q. Name the two dielectric whose molecules have (i) non-zero & (ii) zero, dipole moment.

Answer; (i) Water is an example of dielectric whose non-zero dipole moment. (ii) silicon is an example of dielectric which has zero dipole moment

Q. What is electrostatic shielding?

Answer; Since inside a hollow charged conductor there are no electric field present. Or can say no electric line of force can enter inside the charged conductor. That kind of hollow charged conductor acts as electrostatic shielding.

Q. What are the applications of electrostatic shielding?

Answer; Being inside your car during thundering you can safe. radio signal cannot penetrate through a metal enclosure, etc.

Q.State the law of conservation of charge.

Answer; Law of conservation of charge states that, in an isolated system the total charge of a system is always conserved. It means, charge can never be created nor be destroyed. It can only be transferred from one body to another.

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