# Electrostatics_21

## Gaussian surface – definition, examples, properties

In this post, we will cover the definition of Gaussian surface and its examples. We will also study the properties of the Gaussian surface.

## Capacitors and their usage

Capacitors and their usage is the topic of this post. The capacitor is a component that has the ability or “capacity” to store energy in the form of an electrical charge producing a potential difference across its plates. In other words, Capacitors are components of electrical circuits that temporarily store electric charge. Capacitors are simple […]

## Capacitors and dielectric – Question & Answer

In this post, we have presented fundamental and conceptual questions and answers based on parallel plate capacitors and dielectrics between the plates. This Capacitor and dielectric Question set will certainly help to build the concepts. Capacitor and dielectric Question & Answer 1 ) A parallel plate capacitor is charged by a battery which is then […]

## Charging and Discharging of a Capacitor

A capacitor is charged by connecting it to a battery or to a constant-voltage power supply to create a circuit. Charge flows to the capacitor from the battery or power supply until the potential difference across the capacitor is the same as the supplied voltage. If the capacitor is disconnected, it retains its charge and […]

## Conducting sphere – Questions (multiple choice MCQ)

1) A hollow, conducting sphere is initially uncharged. A positive charge, +q1, is placed inside the sphere, as shown in the figure. Then, a second positive charge, +q2, is placed near the sphere but outside it. Which of the following statements describes the net electric force on each charge? Answer Options: a) There is a […]

## The electrostatic field inside any isolated conductor is always zero

The electrostatic field inside any isolated conductor is always zero. In a cavity in a conductor, the net charge and the electric field are always zero. Let’s see how we can say that. Note that, these are important consequences of Gauss’s Law. The electrostatic field inside any isolated conductor is always zero Let’s suppose a […]

## Energy Stored in Capacitors – numerical worksheet

In this post, we have presented a collection of numerical problems on Energy Stored in Capacitors in the form of a numerical worksheet. This is good for grade 11 and grade 12 students. Energy Stored in Capacitors – worksheet | numerical problems Q1: A large capacitor has plates with areas of 1.5 m2 that are […]

## Parallel-Plate Capacitors – numerical worksheet

In this post, we have presented a collection of numerical problems on Parallel-plate capacitors in the form of a numerical worksheet. This is good for grade 11 and grade 12 students. Parallel-Plate Capacitors – worksheet | numerical problems Q1 ) A synthetic sweater becomes statically charged by friction. The sweater and the skin beneath it […]

## Polarization of a Dielectric between parallel plates of a capacitor

In this post, we will see how Polarization of a Dielectric between parallel plates of a capacitor happens with the help of an external electric field. The potential difference V0 between the plates of a capacitor is reduced to V0/K when a dielectric is introduced. K is the dielectric constant. The potential difference is reduced […]

## Numerical problem on dielectric strength of capacitor

In this post, we will solve a numerical problem on the dielectric strength and dielectric constant of capacitor, maximum electric field, maximum potential difference, maximum charge, etc. Numerical problem on dielectric strength & dielectric constant – solved Question: A parallel-plate capacitor has plates of dimensions 2.0 cm by 3.0 cm separated by a 1.0-mm thickness […]

## Electrolytic Capacitors

An electrolytic capacitor is often used to store large amounts of charge at relatively low voltages. Structure of electrolytic capacitors | dielectric formation This device, shown in Figure 1, consists of a metallic foil in contact with an electrolyte. Electrolyte is a solution that conducts electricity by virtue of the motion of ions contained in […]

## Dielectric strength

Dielectric strength of a dielectric is the maximum electric field that the dielectric can withstand with its insulating properties intact. In other words, the dielectric strength equals the maximum electric field that can exist in a dielectric without electrical breakdown. If the magnitude of the electric field in the dielectric exceeds the dielectric strength, then […]

## Series Combination of capacitors

Series Combination of capacitors Two capacitors connected as shown in Figure 1a and the equivalent circuit diagram in Figure 1b are known as a series combination of capacitors. The left plate of capacitor 1 and the right plate of capacitor 2 are connected to the terminals of a battery. The other two plates are connected […]

## Parallel Combination of capacitors

Parallel Combination of capacitors Two capacitors connected as shown in Figure 1a are known as a parallel combination of capacitors. Figure 1b shows a circuit diagram for this combination of capacitors. The left plates of the capacitors are connected by a conducting wire to the positive terminal of the battery and are therefore both at […]

## Energy density in charged parallel plate capacitor

In this post, we will derive the equation of the Energy density in charged parallel plate capacitor. Energy stored in parallel plate capacitor U = (1/2) C V2 where, C is the capacitance of the capacitor and V is the potential difference between the two parallel plates of the above said capacitor. We know, that […]

## Energy stored in combination of Capacitors

Energy stored in combination of Capacitors equals the sum of the energies stored in individual capacitors. Let’s see how we can show this mathematically using equations. To find out the Energy stored in combination of Capacitors, we need to find out the equivalent capacitance (Ceq) and use this value in the equation of stored energy. […]

## Defibrillator

Defibrillator – application of Capacitors in the medical field One gadget in which capacitors play a significant role is the defibrillator. A defibrillator has a large capacitor and when it is fully charged it can store a Maximum of 360 Joule of energy in its electric field. The defibrillator is quite fast to deliver all […]

## Voltage – Work done in separating charges

In this post, we discuss the concept of voltage (or Potential Difference) in terms of work done in separating charges. Moving charges give rise to electricity. For charges to move, there must be some force to be applied on these charges, and this force can be caused by other positive or negative charges. Consider the […]

## Capacitance of parallel plate capacitor – formula derivation

At a point between two plates of the parallel plate capacitor, the Electric field generated by the combined effect of the 2 plates of the capacitor can be expressed as: E = σ /2 ε0 + σ /2 ε0 = σ / ε0 [ note that the electric field produced by a plane sheet of […]

## Bending Water stream by charged rubber rod – how?

When a charged rubber rod is brought close to a thin stream of water, the water is attracted toward the rod and the stream is bent. Water molecules have a permanent separation of charge or regions of different charges. Such molecules are called polar molecules. Charged rod brought close to a small stream of water […]

## Touch screens: resistive & capacitive – working principle

Touch screens are quite common these days. In this post, we will discuss the physics behind the working principles of different touch screens. Specifically speaking, we will cover here the working principles of Resistive Touch Screens and Capacitive Touch Screens. Resistive Touch Screens One of the most common touch screens we experience is found at […]

## How charged rubber comb attracts pieces of paper?

When a negatively charged rubber comb is brought near small pieces of paper, the charges in the paper molecules are acted on by electric forces – positive charges are attracted, negative charges repelled – and the result is an effective separation of charge. The molecules are then said to be polarized: they possess definite regions […]

## Law of charges & Coulomb’s law – difference

In this post, we will talk about the difference between the law of charges & Coulomb’s law. An electric force exists between any two charged particles. On observation, it is found that the mutual forces on the particles may be either attractive or repulsive, depending on the types of charges (+ or -). In fact, […]

## Capacitor & Capacitance – formulas

A bunch of important formulas related to Capacitance & capacitors are listed below. capacitance of a conductor & capacitance of a spherical conductor – formulas capacitance of parallel plate capacitors with or without dielectric slab, Potential energy – formulas equivalent capacitors, redistribution of charge – formulas

## Principle of a capacitor – step by step

Principle of a capacitor The principle of a capacitor is based on two physical events. These are as follows: 1 ) The capacitance of a conductor increases by a small amount when another uncharged conductor is placed near it.2 ) The capacitance of a conductor increases greatly when an earth-connected conductor is placed near it. […]

## Capacitance of a Spherical Conductor (with formula derivation)

In this post, we will discuss and derive the formula of the Capacitance of a Spherical Conductor. derivation of the Capacitance of a Spherical Conductor Suppose an isolated spherical conductor of radius a metre is placed in a vacuum (or air). Suppose a charge of +Q coulomb is given to the sphere. The charge spreads […]

## Electric field due to two infinite plane parallel sheets of charge

Consider two infinite plane parallel sheets of charge A and B, having surface charge densities equal to σ1 and σ2 respectively. (see the figures 1 to 4 in the following sections). Note that, In a sheet of charge, the same charge shows up on its two sides. On the other hand, since a plane & […]

In this post, we will find out what a Faraday cage is and how this is related to lightning strikes. What is a Faraday Cage? A Faraday Cage, named after British physicist Michael Faraday, is a cage, metal grating, or metallic box that can shield electrical charge. Charges gather on the outer shell of the […]

## Van de Graaff generator – important questions

In one of the earlier posts, we discussed the working principle and the physical structure of the Van de Graaff generator. In this post, we will answer a few important Questions on the Van de Graaff generator. Here are those Questions on the Van de Graaff generator with answers. What happens if you touch the […]

## Class 12 Physics Question Bank – Electrostatics

This post presents a Physics Question Bank for class 12 covering the Electrostatics chapter. Definition type questions from the Electrostatics chapter 1) Define electric flux. 2) Define electric dipole moment ofan electric dipole. 3) Define the dielectric constant of a medium. 4) Define quantization of electric charge. 5)Define the following terms : (i) Electric field […]

## Equilibrium of electric forces on charges on one line & formulas

In this post, we will take a few cases where the Equilibrium of electric forces on charges on one line happens. In every case, there are 3 charges on one line. We will list down the specific equilibrium condition of each such case and the formula of equilibrium for that scenario. Scenario 1 (Equilibrium of […]

## Drawing the field lines due to a dipole

How to draw the field lines due to a dipole? Fig. 1 depicts the field lines due to a dipole. For a dipole, field lines start from the positive charge and terminate on the negative charge. The number of lines leaving the positive charge is equal to the number of lines terminating on the negative […]

## Electric Field due to a Plane Sheet of Charge

Electric Field due to a thin infinite Plane Sheet of Charge In this section, we will derive the equation for the Electric Field due to a thin infinite Plane Sheet of Charge. Consider a thin infinite plane sheet of charge ABCD, charged uniformly with surface charge density σ. Note that, in a thin infinite plane […]

## electrostatics – Worksheet 1 problem solution (Q4)

4) A positively charged object Q is placed as shown in the sketch. The potential difference between two points A and B is 4 x 10-4 V. (a) Calculate the change in electrical potential energy of a +2nC charge when it moves from A to B.(b) Which point, A or B, is at the higher […]

## electrostatics – Worksheet 1 problem solution (Q3)

3 ) A charge of +5nC is moved by a distance of 4 cm against a uniform electric field of magnitude 2 x 1012 NC-1 from A to B. (a) Calculate the work done in moving the charge from A to B.(b) The charge is now released and returns to A. Calculate the kinetic energy […]

## electrostatics – Worksheet 1 problem solution (Q2)

Question 2) In the picture below, X is a small negatively charged sphere with a mass of 10kg. It is suspended from the roof by an insulating rope which makes an angle of 60o with the roof. Y is a small positively charged sphere that has the same magnitude of charge as X. Y is […]

## electrostatics – Worksheet 1 problem solution (Q1)

1 ) Determine the electrostatic force and gravitational force between two electrons 1ºA apart (i.e. the forces felt inside an atom) [ here is the complete worksheet: electrostatics worksheet 1 ] Solution: Getting everything into S.I. units: The charge on an electron is 1.6×10-19C, the mass of an electron is 9.11 x 10-31kg, and 1ºA=1 […]

## Numerical problems on Electrostatics – worksheet 1

In this post, we publish a worksheet containing a bunch of numerical problems from the Electrostatics chapter of HS physics. This numerical set includes problems based on Coulomb’s force or electrostatic force, electric field, electric potential, electric potential energy, etc. Links to the solutions of the numerical problems will be found beside every problem. This […]

## Electric Field Due to a Short Dipole – formulas

In this post, we will study 2 formulas of the electric field due to a short dipole. These electric field formulas represent the following: (1) Electric Field Due to a Short Dipole at a point P on its axis & (2) Electric Field Due to a Short Dipole at a point on the equatorial line. […]

## Electric flux – definition, formula

Electric flux – definition, formula – In this post, we will define electric flux and study its equation. We will also study a few figures that come with numerical problems related to electric flux. Later, we will find the statement of Gauss’ theorem. Electric Flux – definition Definition of flux: The total number of electric […]

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