Electrostatic Potential and Capacitance Notes Class 12 CBSE Physics Chapter 2 (Free PDF Download)

Section-A (1 Mark Questions)

1. A 500 µC charge is at the centre of a square of side 10 cm. Find the work done in     moving a charge of 10 µC between two diagonally opposite points on the square.

Ans. The work done in moving a charge of 10 µC between two diagonally opposite points on the square will be zero because these two points will be at equipotential.

2. What is the electrostatic potential due to an electric dipole at an equatorial point?

Ans. Electric potential at any point in the equatorial plane of the dipole is Zero.

3. What is the work done in moving a test charge q through a distance of 1 cm along the equatorial axis of an electric dipole?

Ans. Since potential for equatorial axis
        V = 0
        ∴W = qV = 0

4. Define the term ‘potential energy’ of charge ‘q’ at a distance V in an external electric field.

Ans. It is defined as the amount of work done in bringing the charge from infinity to its position in the system in the electric field of another charge without acceleration.
V = Er.

5. What happens to the capacitance of a capacitor when a dielectric slab is placed between its plates?

Ans. The introduction of dielectric in a capacitor will reduce the effective charge on plate and therefore will increase the capacitance.

Section-B (2 Marks Questions)

6. Why does the electric field inside a dielectric decrease when it is placed in an external electric field?

Ans. The electric field that is present inside a dielectric decreases when it is placed in an external electric field because of polarisation as it creates an internal electric field which is opposite to the external electric field inside a dielectric due to which the net electric field gets reduced.

7. The electric potential V at any point in space is given $V=20x^{3}$  volt, where x is in meter. Calculate the electric intensity at point P=(1,0,2)

Ans. We know that the following relation exists between electric field (E) and potential (V)

         E=\dfrac{-dV}{dx}

Here

$V=20x^{3}volts$

So,

$E=\dfrac{d(20x^{3})}{dx}$

Or

$E=60x^{2}$

Here 

x=1

Thus, 

$E=60\cdot (1)^{2}=60N/C$

8. With the help of an example, show that farad is a very large unit of capacitance.

Ans. Assuming that we want a capacitance of 1 farad with a distance of 1 cm in between both plates, the area of both the plates will be nearly $12\times 10^{-8}$ square metres. As such dimensions are not possible, we conclude that the Farad is a very large unit of capacitance

9. The potential at a point A is –500V and that at another point B is +500V. What is the work done by an external agent to take 2 units (S.I.) of negative charge from B to A.

Ans. Here we will use the formula:

$dW=Q\cdot dV$ where W = work done; Q = charge (SI unit = coulomb); dV = potential difference

Integrating the above equation we get,

$\Rightarrow W-O=Q(V_{f}-V_{i})$ ;

$\Rightarrow W=2\cdot (V_{A}-V_{B})$ ;

$\Rightarrow W=2\cdot (-500-500)$ ;

$\Rightarrow W=-2000J=kJ$ ;

10. A Can two equipotential surfaces intersect each other? Give reasons. Two charges –q and +q are located at points $A=(0,0,-a)$ and $B=(0,0,+a)$ respectively. How much work is done in moving a test charge from point $P=(7,0,0)$ to $Q=(-3,0,0)$ ? (zero)

Ans(i) No

Reason: At the point of intersection, there will be two different directions of electric field, which is not possible.

 (ii) Work done in moving the test charge atom P to Q is zero.

Reason: Test charge is moved along the equatorial line of an electric dipole. As potential at every point on equatorial line is zero, so work done,

$W=q_{0}(V_{Q}-V_{P})=q_{0}(0-0)=0$

PDF Summary - Class 12 Physics Electrostatic Potential and Capacitance Notes (Chapter 2)

Electrostatics 

The section of CBSE Class 12 Physics electrostatic potential and capacitance notes mainly deals with the in-depth analysis of electromagnetic phenomena when they are not performing any movements. Additionally, it is divided into ten further sub-topics to study the companion processes of reaching the state. These are -  

1. Electric charge 

In this section of Physics ch 2 Class 12 notes, you get to learn about the basic features of electric charge and its expression in Physics. Along with its basics, the sections help to understand the full potential of charge. Different aspects of Charge included in Class 12 Physics Chapter 2 notes are -

• Definition 

• Type: Positive and Negative Charge

• Unit and dimensional formula

• Point Charge 

• Properties of Charge 

• Comparison of Charge and Mass 

• Methods of Charging

• Electroscope 

2. Coulomb's Law 

Force is created when charges of opposite signs attract each other, and they repulse if the signs are the same. Coulomb's law tries to define this phenomenon through a mathematical formula, explicitly mentioned in Physics Class 12 notes Chapter 2. Moreover, there is key information about the variation of the constant k and its effect on a medium. Coulomb's law's vector form and the principle of superimposition are also explained in ch 2 Physics Class 12 notes.

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3. Electric Field 

As stated in Class 12 Physics Chapter 2 notes, every positively or negatively charged particle has their respective electric fields. It feels a force at the time of interaction which might be attraction or repulsion. As it arises from electric charge, it is crucial to know about its different parts like -

• Electric field intensity 

• Relation between electric force and electric field 

• Super imposition of electric field 

• Point charge 

• Continuous charge distributions 

• Properties of Electric Field Lines 

• Motion of Charged Particles in an Electric field 

Learning more about the electric field from electric potential and capacitance notes Class 12 helps a student to get a grasp of upcoming chapters. 

4. Electric Potential Energy 

When energy helps a charge to move from an electric field, it is known as the Electric Potential Energy. This section of electrostatic chapter Class 12 notes requires a student to study the Electron volt (eV), and the potential energy that an n number of charges can hold. 

5. Electric Potential

This section of Class 12 Physics Chapter 2 notes focuses on in-depth learning of Electric Potential or Voltage. Basically, it defines the potential movement of energy. 

6. Relation between Electric Field and Potential 

Apart from knowing more about the relationship between the two values, Physics Class 12 Chapter 2 notes also discuss equipotential surfaces. 

7. Electric Dipole 

Essentially, 'Dipoles' are two opposite points of charge represented with q and –q, with their distance between each other being 2a. Electric Dipoles are crucial in your study of Physics Class 12 Chapter 2 notes to learn more about electric fields and their potential.

Additionally, Class 12 Physics Chapter 2 notes focus on the influence of electric dipoles on a uniform electric field mainly through Force and Torque, Work, and Potential Energy. 

In the last part of Electrostatics, further focus is on using the formulas to their fullest potential. It includes subsections of Electric Field, Electric Potential Energy, Electric Potential, and Electric Dipole. In the notes for electrostatic potential and capacitance, you will find proper solutions accompanied by clear and crisp diagrams for better understanding. 

8. Gauss's Law

Apart from just discussing the Gauss's Law, in Physics Class 12 ch 2 notes there is a thorough explanation of its properties and applications. The Gauss' Law states that net electric flux passing through a hypothetical closed surface is equal to the net electric charge present within the same closed surface. Being a broad part of the whole chapter, you may need to spend a little more time on it. Moving forward, it starts discussing the properties of conductors in relation to Gauss's Law. The Class 12 Physics notes Chapter 2 perfectly defines the journey to Gauss' Law from Coulomb's Law. 

Here is the Gauss's Law present in the Class 12 Physics ch 2 notes, 

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9. Capacitors 

There is a dedicated section about Capacitors in the Class 12 Physics Chapter 2 notes elucidating its functions and importance as storage of potential electric energy. After explaining the structure of a capacitor, it points out the different types, parallel plate, spherical and cylindrical. The section of Chapter 2 notes of Physics Class 12 is further divided into subheads like: 

• Properties of an ideal battery

• Grouping of capacitors 

• Simple circuits (Series and Parallel) 

• Dielectric 

• Van de Graaff generator

• Combination of drops 

• Charge distribution method 

• Wheatstone Bridge-based circuit 

• Extended Wheatstone Bridge 

• Infinite network of capacitors

• Redistribution of charge between two capacitors 

Vedantu prepares the Class 12 Physics Chapter 2 notes with help from subject matter experts. In the PDF, you get a comprehensive idea of the topic along with potential answers to the most asked questions. Furthermore, the detailed explanation on each section and subsections are written in a simple language allows a student to ace their exams with wholesome knowledge.

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Important Questions

1. A charge of 4 × 10–8C is uniformly distributed on the surface of a spherical conductor, having a radius of 15 cm. Determine the electric field just outside this sphere at a point that is 15 cm from the centre of this sphere.

2. Determine the capacitance given that the distance between the two plates has been reduced by half and the parallel plate capacitor holds a capacitance of 20 pF (where 1pF = 10-12 F) having air between the two plates.

3. What will be the total capacitance of a combination where three capacitors, each having a capacitance of 20 pF, are connected in series.

4. A square having a side of 10 cm has a 500 µC charge at its centre. Determine the work done to move a charge of 10 µC between two points that are diagonally opposite each other on the square. 

5. At an equatorial point, what will be the electrostatic potential because of an electric dipole? 

6. Calculate the work done to move a test charge, q, through a length of 1 cm along the equatorial axis of an electric dipole?

Polarisation

A capacitor has its plates enclosed in a medium that can be filled by insulating substances. A net dipole moment is then induced by an electric field in the dielectric. This event causes the field in an opposite direction. 

Equipotential Surface

An equipotential surface is a type of surface where the potential always has a constant value. If considered as a point charge, the concentric spheres that are centred at a particular area of this charge are basically equipotential surfaces.

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