Physics notes are a crucial tool for boosting your NEET 2022 preparations. While covering any chapter, students are advised to write down notes to compile all the lengthy topics in a short form. These notes help students during the final revision before the exam and during the practice sessions. Moreover, students can easily do a quick revision of all the learnt topics by referring to the notes throughout the preparation. Regular revisions of NEET 2023 Important Chapters are highly recommended to boost the memory power and be exam ready at any stage of preparation.
As the NEET UG 2023 exam date is getting closer, aspirants must cover multiple chapters every day to revise NEET 2023 Syllabus efficiently. This article provides important notes for the Physics chapter Electric Charges and Fields.
What is Electric Charge?
Electric charge is the amount of electrons or energy that transfers from one body to another through different modes like induction, conduction, or other specific methods. Two types of electrical charges are present in most bodies, i.e., positive charge and negative chargers. However, bodies without any charge are considered neutrally charged.
Universally charge is denoted by ‘q’, and its unit is termed Coulomb. In Mathematical terms, electric charge is defined as the total charge carried in a single electron multiplied by a total number of electrons. It is symbolically represented as:
Here Q represents a charge, n represents the number of electrons, and e represents the charge on one electron.
Electric charges have two fundamental natures:
- Same charges repel each other.
- Opposite charges attract each other.
The nature of charges is determined by the force acting on them and how that force coordinates the flow of the charge. The charge in both electrons and protons is equal. The only difference lies in the sign of denoting them. Electron is denoted with a – or negative sign, and a proton is denoted with a + or positive sign.
Understanding the Properties of electric charge
Electric charge is a scalar quantity
This means that we can add or subtract electrical charges mathematically.
Electrical charge is connected with mass
This property denotes that a charge can never exist without mass. However, a mass can be present in the absence of an electrical charge. This phenomenon can be understood with the help of the following example:
- A particle, say, a photon or neutron that has zero mass, does not have any electrical charge.
- A beam of ray deflected by an electric or magnetic field will carry a charge, and the particles in the ray will carry a mass. On the other hand, if the same beam is not deflected by either a magnetic or electric field, it will not carry any charge. However, it may consist of particles with mass.
The electrical charge is transferable
Electrical charge quickly transfers from one body to another when kept in contact with each other. If an uncharged body is kept in contact with a charged body, the uncharged body will quickly get charged by the transfer of electrons.
Electrical charge is quantised
This property of electric charge denotes that any charge is quantised if the physical quantity has discrete values.
Electrical charge is invariant
This property explains that an electrical charge is independent of any frame of reference. The charge of a mass does not change with the speed of the mass. However, the charge density is dependable on the speed, and it increases with the increase in speed.
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Electrical charge is conserved
According to this property, the total charge in an isolated system does not change with time. Therefore, it is said that a charge can neither be destroyed nor created. This property holds its value in every type of reaction like nuclear, chemical, or decay. Moreover, it has not witnessed any exception to date.
Charge produces energy at acceleration
According to electromagnetic theory, a charged particle produces only an electric field at rest. However, when the charged particle is accelerated, it produces heat in the electromagnetic waves and electric and magnetic fields.
Methods of Charging a body
There are three methods of charging a body:
Charging by friction
In this method, two bodies are rubbed together to generate energy. During energy generation, one body gets positively charged, and the other is negatively charged. An example of this charging method is rubbing a nylon scale on hair. During this process, the scale gets positively charged, and the human hair gets negatively charged. Another example can be rubbing wool against ebonite. In this process, wool gets positively charged while the ebonite gets negatively charged.
Charging by conduction
In this process, the charge is transferred between two conductors. When two conductors (one charged and another uncharged) are brought in contact with each other, they both get equally charged by the repulsion of charge between them.
Charging by induction
In this process, when an uncharged body is brought near a charged body, the charged body attracts the opposite charge and repels an equal amount of charged particles to the uncharged body. Due to this process, the uncharged body gets equally charged with the previously charged body.
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What is Meant by Coulomb’s Law?
According to Coulomb’s Law, the force of repulsion or attraction between two charged points is directly proportional to the product of the given two charges and inversely proportional to the square of the distance between these two charges.
Coulomb’s law can be understood by the following equation:
Suppose q1 and q2 are two charges, F is the force between them, and r is the distance between the charges; then, according to Coulomb’s law
F q1 q2
From the above-mentioned equations, it can be said that F q1 q2r2 or F= K q1 q2r2 , here K is proportionality constant.
Electrical Field and its Physical Significance
An electric field is the mathematical representation of the magnitude and direction of the total electrical force experienced by one unit of electric charge. It is measured and represented by a volt per metre or Newton per Coulomb. An example of an electrical field is- the electric field of a given isolated positive unit, which consists of field lines that radiate away from the charge and diminish in strength with the inverse square of the distance.
The following points elaborate on the physical significance of the electric field:
- The electric field gives the direction and magnitude of the electrical force.
- Electric field assists in knowing the electric force that is experienced by a single positive charge when it is placed at a given point in a system that has multiple charges.
- The electric field intensity concept is crucial for time-varying electromagnetic properties.
What are Electrical Field Lines and their Properties?
Electrical field lines are imaginary lines that are drawn through a region. These lines are constructed so that their tangents at a given point are in the direction of the electric field at that point.
The following points elaborate on the properties of electric field lines:
- The total number of field lines that either originate or terminate on a charge is directly proportional to the intensity of the charge.
- Electric field lines arise from a positive charge and end at a negative charge.
- The total number of field lines that pass through the perpendicular unit area corresponds to the magnitude of the electric field.
- Two or more electrical field lines never meet or intersect each other.
- Electrical field lines never form a loop.
- A tangent to a particular field line at any given point provides the direction of the electric field line at that specific point.
- Uniform electric field lines are parallel, straight and appropriately placed to each other.
- Electric field lines flow from higher to lower potential.
- Electrical field lines never exist inside a conductor.
GAUSS’s Law and its Critical Points
GAUSS’s law relates an electric field to the total flux through a closed surface to the total charge enclosed by that surface. According to this law, the total flux linked with the closed surface is 1/0, the charge captured by the closed surface.
Crucial points of the GAUSS’s Law are:
- GAUSS’s Law is similar to Coulomb’s Law. By assuming GAUSS’s Law, Coulomb’s Law can be proved or vice-versa.
- This Law relates the total flux of a closed surface to the energy enclosed by the closed surface.
NEET 2023 Physics chapter Electric Charges and Fields is lengthy, and students need to dedicate sufficient time to cover all the topics thoroughly. In addition, NEET aspirants must practise all the questions and numericals given in the textbook to improve their problem-solving skills. Important notes on Electric charges and Fields are a must during revisions. By referring to these notes, aspirants can quickly revise all the crucial concepts and laws to boost their exam preparations.