# CLASS 12  PHYSICS-- Chapter 1: ELECTROSTATICS

This is a discussion on CLASS 12  PHYSICS-- Chapter 1: ELECTROSTATICS within the 12th forums, part of the Classes category; CLASS 12  PHYSICS Chapter 1: ELECTROSTATICS Short answer question: Q1. An electrified rod attracts pieces of paper. After a ...

1. ## CLASS 12  PHYSICS-- Chapter 1: ELECTROSTATICS

CLASS 12  PHYSICS

Chapter 1: ELECTROSTATICS

Q1. An electrified rod attracts pieces of paper. After a while these pieces fly away. Why?

Ans. When electrified rod is brought close to the pieces of paper, by induction an opposite charge appear on pieces of paper due to which these pieces of paper attracted towards the rod. But when these pieces of paper touches the charged rod, charge of rod transfer to the pieces of paper due to which there will be the force of repulsion between rod and pieces of paper, hence the pieces of paper fly away from the rod.

Q2. Is it possible for electrostatic field lines to intersect?? Explain.

Ans. The electrostatic field lines never cross each other, because the electric intensity at point in electric field has one direction, which is along the tangent to electric field lines. If the electrostatic field lines cross each other; then the electric intensity would have more than one direction, which is physically not possible.

Q3. An uncharged conducting spherical shell is placed in the field of a positive charge q. what will be net flux through the shell?

Ans. As the uncharged conducting spherical shell contains no charge, by Gausses law, the flux through the shell is zero. But due to external positive charge becomes negatively charge and other becomes positively charged. At the negative charged face the electric field lines entering the shell, so the electric flux lines are leaving the shell so the electric flux is positive. As the number of lines of force entering the shell being equal to number of lines of force leaving the shell, therefore the total flux due to external charge is also zero.

Q4. What is the difference between the electric potential and electric potential energy at any point of an electric field?

Ans. The electric potential energy of a charge in an electric field is the work done by an external agent to move this charge against the electric field from low potential to the point in the electric field. But the potential energy per unit charge at a point in electric field is called electric potential.

Q5. The electric potential is constant throughout a given region of space. Is the electric field zero or non-zero in this region? Explain
Ans. As the electric potential in the given region of space is throughout constant, therefore the potential difference in this region of space is zero when the potential difference ∆v is zero, then the electric field E must be zero.

Q7. Do electrons move up or fall down a potential gradient?

Ans. The potential gradient the electric field intensity E at point in electric field, which is directed from high potential to low potential. An electrons being a negative charge particle, therefore will tend to move from low potential to high potential, hence will move up the electric field.

Q8. Describe the force or forces on a positive point charge when placed between parallel plates,

(a) With similar and equal:
When the point positive charge is placed between parallel plates with similar and equal charges, then the net force on this point positive charge is zero. The force of repulsion on this point positive charge due to these plates is equal in magnitude but opposite in direction cancel each other, so the net force on point charge is zero and hence this point charge will remains at rest.
(b) With opposite and equal charges:
When this positive point charge be placed between parallel plates having an equal but opposite charges then there exists a force of repulsion due to positive charge plate and force of attraction due to negative charge plate. These two forces on the point charge are directed from positive to negative plate, hence support each other due to which there will be net force on this point positive charge which will move it from positive plate to negative plate.

Q9. Describe the charging of a capacitor by a battery, assuming that positive charges are transferred.

Ans. Consider a parallel plate capacitor which is connected to a battery such that positive terminal of the battery is connected to the plate A and negative terminal to the plate B. if we assume that a positive charges are to be transfer. This positive charges are to be transfer. This positive charge from the positive terminal of the battery is transferred to the plate A due to which plate A charges positively. This positive charge on plate A will attract the free electron of the plate B due to which there will appear a negative charge on the plate B. the positive charge from plate B will move to negative terminal of the battery. Thus the same positive charge, which moves from the positive terminal of the battery through the capacitor, reaches back to the negative terminal of the battery.

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3. ## Re: CLASS 12  PHYSICS-- Chapter 1: ELECTROSTATICS

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