Applied Physics Unit 2 - Electrostatics PDF

**Unit 2** **Electrostatics** [**Electric charge** ] It is the [physical property](https://en.wikipedia.org/wiki/Physical_property) of [matter](https://en.wikipedia.org/wiki/Matter) that causes it to experience a [force](https://en.wikipedia.org/wiki/Force) when placed in an [electromagnetic fiel...

**Unit 2** **Electrostatics** [**Electric charge** ] It is the [physical property](https://en.wikipedia.org/wiki/Physical_property) of [matter](https://en.wikipedia.org/wiki/Matter) that causes it to experience a [force](https://en.wikipedia.org/wiki/Force) when placed in an [electromagnetic field](https://en.wikipedia.org/wiki/Electromagnetic_field). Electric charge can be *positive* or *negative*. **Positive charges** are associated with protons, which are subatomic particles residing in the nucleus of an atom. They are represented by the symbol "+". **Negative charges** are linked to electrons, which orbit the atomic nucleus and are denoted by the symbol "-".  When an object carries a negative charge, it possesses an excess of electrons compared to protons. Conversely, a positive charge indicates an excess of protons relative to electrons. **[Electric field]** An **electric field** is defined as the region surrounding an electrically charged object. Within this field, any other charged objects will experience an electromagnetic force. The formula of the electric field is given as, *E *= *F */*Q* Where, E is the electric field.\ F is the force.\ Q is the charge. The direction of the field is taken as the direction of the force which is exerted on the positive charge. The electric field is radially outwards from the positive charge and radially towards the negative point charge. **[Electric potential]** The **electric potential**  is defined as the amount of [work](https://en.wikipedia.org/wiki/Work_(physics)) energy needed per unit of [electric charge](https://en.wikipedia.org/wiki/Electric_charge) to move this charge from a reference point to the specific point in an electric field. ------------- ------ **SI Unit** Volt ------------- ------ **[Electrical potential difference]**  **[Equipotential lines]** An equipotential line is *a line along which the electric potential is constant*. An equipotential surface is a three-dimensional version of equipotential lines. Equipotential lines are always perpendicular to electric field lines. Equipotential Lines [Electric Potential Due to a Point Charge] ------------------------------------------------------ The electric potential at a point in an electric field is the amount of work done moving a unit positive charge from infinity to that point along any path when the electrostatic forces are applied. Suppose that a positive charge is placed at a point. The charge placed at that point will exert a force due to the presence of an electric field.  The electric potential at any point at a distance r from the positive charge +q is shown as:  Where r is the [position vector](https://byjus.com/physics/position-and-displacement-vectors/) of the positive charge and q is the source charge. As the unit of electric potential is volt, 1 Volt (V) = 1 joule coulomb^-1^(JC^-1^) When work is done in moving a charge of 1 coulomb from infinity to a particular point due to an electric field against the electrostatic force, then it is said to be 1 volt of the electrostatic potential at a point. **[Columbs law]** According to **Coulomb's law**, the force of attraction or repulsion between two charged bodies is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. It acts along the line joining the two charges considered to be point charges. **Application of Coulomb's Law** - To calculate the distance and force between the two charges - The electric field can be calculated using Coulomb's law E = F/ Q~T~ \[N/C\] Where, E = Strength of the electric field F = Electrostatic force Q~T ~= Test charge in Coulombs - To calculate the force on one point due to the presence of several points (Theorem of superposition). **[Capacitance]** *Capacitance* is the capability of a material object or device to store electric charge. The unit of capacitance is the Farad (F) and a 1F capacitor charged to 1V will hold one Coulomb of charge. **[Capacitor]** A capacitor is a device, which increases the capacitance of a conductor. It usually consists of two conductors; one is charged and the other is earthed. The space between the plates is filled with some insulating material called dielectric. The capacitance of a capacitor depends on \(i) area of overlap between two plates \(ii) distance between the plates \(iii) nature of dielectric medium. **[Principle]** When it is negatively charged, there is a rise in negative potential, and its capacitance is very small. When a second similar conductor B is brought very nearer to the first, positive charges are induced in B by electric induction. This positive charge decreases the negative potential on A. Hence, for the same charge Q, the potential V has fallen. Since C = Q/V, The capacitance of the first conductor increases.  Capacitors are used \(i) to store electric charges, \(ii) to measure potential difference and small currents, \(iii) to reduce voltage fluctuations, generating oscillations, for providing time delay in various electric circuits, and \(iv) to obtain required electric field. - **Capacitors are connected in parallel**, the total capacitance in the circuit is equal to the sum of the individual capacitance. If three capacitances, C1, C2 and C3 are connected in parallel, then the total capacitance C is given by the relation: **C = C1 + C2 + C3** - **Capacitances are connected in series**, then the total capacitance is given by the relation: **1/C = (1/C1) + (1/C2) + (1/C3)** **[Dielectrics ]** A dielectric is an insulating material in which all electrons are tightly bound to the nucleus of the atom. There are no free electron to carry current, e.g ebonite mica and oil. The electrons are not free to move under the influence of an external field. **[Capacitor charging and discharging ]** Consider a capacitor connected to a battery of potential V~0~ and the resistance R through a switch S. when the switch is on electrons flow to the capacitor initially and the charge is built up. The charge develops a potential across the capacitor. At one stage the potential across the capacitor is equal to the potential of the battery, at which the electron flow is stopped. This means that the force offered by the battery on the electron is equal to the force given by the capacitor but opposite in nature. Now the capacitor is said to be fully charged. Alternatively, The discharging of a capacitor is *the process through which stored charge within the capacitor is released*.