Table of contents | |
What is an Electric Charge? | |
Properties of Electric Charge | |
Conductors and Insulators | |
Concept-Based Questions | |
Frequently Asked Questions |
All of us have the experience of seeing a spark or hearing a crackle when we take off our synthetic clothes or sweaters, particularly in dry weather. Have you ever tried to find any explanation for this phenomenon? It can be attributed to electric charges.
In this EduRev document, we will delve into the concepts of Electric Charges and Fields, specifically focusing on their definition, formula, properties, unit, and more, as covered in Class 12 Physics.
Electric charge is a fundamental property of matter that determines how it interacts with other charged matter and electric fields. This property is carried by subatomic particles, with protons carrying a positive charge, electrons a negative charge, and neutral particles having no charge.
Two kinds of electric charges are there:
Positive Charge: When an object has a positive charge it means that it has more protons than electrons.
Negative Charge: When an object has a negative charge it means that it has more electrons than protons.
When there is an identical number of positive and negative charges, the negative and positive charges would cancel out each other and the object would become neutral.
The electric charge is measured using a coulomb.
“One coulomb is the quantity of charge transferred in one second.”
Mathematically, the definition of a coulomb is represented as:
Q = I.t
In the equation, Q is the electric charge, I is the electric current and t is the time.
A charge is a derived physical quantity. The charge is measured in coulomb in the S.I. unit.
In practice we use:
Note:
- Charge of a single electron = -1.602 × 10-19 C
- Charge of a single proton = + 1.602 × 10-19 C
- Charge of a single neutron = 0 C
No, electric charge is a scalar quantity.
Notice that we only considered the numerical values and their signs (positive or negative) when adding. There was no need to consider any direction associated with the charges. This illustrates that charge is a scalar quantity: it only has magnitude (how much charge) and sign (positive or negative), but no direction.
2. Electric Charge is a scalar quantity: It follows scalar laws of operations, i.e. it adds algebraically and represents the excess of electrons in a negatively charged atom or a deficiency of electrons in a positively charged atom.
3. A charge is transferable: Electric charge can be transferred from one body to another, but there is a restriction to the charge transfer. Only electrons are transferred from one body to another because protons are tightly bound to the nucleus of every atom. Hence, the body which loses electrons in the transfer becomes positively charged, and the body which receives electrons becomes negatively charged.
- A neutral body has a number of electrons = number of protons
- A positively charged body has a number of electrons < number of protons
- A negatively charged body has a number of electrons > number of protons.
4. Charge is always conserved: In an isolated system, the total charge (sum of positive and negative) remains constant whatever charge transfer takes place in the system internally. It is called the principle of charge conservation.Conservation of Charge5. Charge is quantized: Charge on anybody always exists in integral multiples of a fundamental unit of electric charge. This unit is equal to the magnitude of the charge on one electron (1e = 1.6 × 10-19 C). So charge on anybody Q = ± ne, where n is an integer and e is the charge on a single electron. This was proved by Millikan's oil drop experiment.
6. Charge is always associated with mass: Yes! Electrons, Protons and Neutrons also have masses.
Their value is determined, experimentally, to be following:
Mass of an electron = 9.109 × 10-31 Kg = 5.49 × 10-4 amu
Mass of a proton = 1.6726 × 10-27 Kg = 1.007 amu
Mass of a neutron = 1.6749 × 10-27 Kg = 1.008 amu
7. Charge is relativistically invariant: This means that charge is independent of the frame of reference, i.e., the charge on a body does not change whatever be its speed. This property is worth mentioning as in contrast to charge, the mass of a body depends on its speed and increases with an increase in speed. You will be exposed to this property later when you will learn The Special Theory of Relativity.
8. A charge at rest produces an only an electric field around itself: A charge at rest creates a region of influence called an Electric Field around itself in space.Electric Field Lines
Charged Comb attracting small pieces of paper
Static electricity refers to an imbalance between the electric charges in a body, specifically the imbalance between the negative and the positive charges on a body.
Any object can be broadly classified in either of the following two categories on the basis of their electrical properties:
(i) Conductors
(ii) Insulators
(i) Conductors: The materials or substances which allow electricity to flow through them are called Conductors. Conductors are able to conduct electricity because they allow electrons to flow inside them very easily.
The general property of conductor is to allow the transition of heat or light from one source to another. Metals, humans, earth and animal bodies fall in the category of conductors. This category generally comprises of metals but may sometimes contain non-metals too.
Example: Carbon in the form of graphite. Conductors have free electrons on its surface which allows current to pass through, that’s why conductors are able to conduct electricity.
Applications of Conductors
Fig: Use of conductors in lightning a bulb
Conductors are quite useful in many ways and used in many real life applications like:
Fig: Insulators
(ii) Insulators: The materials or substances which resist or don’t allow the current to flow through them are called Insulators. Insulators are mostly solid in nature and are used in a variety of systems. Insulators don’t allow the flow of heat as well.
The property which makes insulators different from conductors is its resistivity. Wood, cloth, glass, mica, and quartz are some good examples of insulators. Insulators are also called Protectors as they give protection against heat, sound and of course passage of electricity.
Insulators don’t have any electrons in its and that’s why insulators don’t conduct electricity.
Examples:
Fig: An insulator is used to protect wire opening
Being resistive to flow of electron, insulators are used worldwide in a number of ways.
Some are as follows:
Q.1. Why have we defined only two types of charges? Why not three or more?
Ans. Only two kinds of electric charges exist because any unknown charge that is found experimentally to be attracted to a positive charge is also repelled by a negative charge. No one has ever observed a charged object that is repelled by both a positive and a negative charge.
Q.2. What happens
(a) When two like charges are brought together?
(b) When two, unlike charges, are brought together?
Ans. (a) When two like charges are brought together, they repel each other with an electrostatic force.
(b) When two, unlike charges, are brought together, they attract each other with an electrostatic force.
Q.3. What does neutral in electric charge mean?
Ans. Neutral does not refer to any third type of charge. It is the absence of any excess or deficiency of electrons in a body, i.e. the number of electrons = number of protons.
Q.4. Does the mass of the body get affected while charging?
Ans. Yes, the mass of the body gets affected because electrons have a definite mass, so the mass of the body slightly increases when it gains electrons while the mass decreases when it loses electrons.
Q.5. Two identical metallic spheres of exactly equal masses are taken. One is given a positive charge q coulombs and the other an equal negative charge. Are their masses after charging equal?
Ans. No, A body is positively charged due to the deficit of electrons while the negative charge is due to a surplus of electrons. Hence, the mass of the negatively charged sphere will be slightly more than that of the positively charged sphere.
Q.6. During a nuclear reaction, what happens to electric charge?
Ans. In the event of a nuclear reaction, the electric charge is conserved considering an isolated system. This is true for any nuclear or chemical reaction. In a nuclear reaction, the parent nuclei undergo a transformation into daughter nuclei, but the total algebraic charge remains constant.
Q.7. Explain the statement: ‘For a body, an electric charge is quantized.
Ans. Considering a particular body, ‘electric charge is quantized’ refers to the number of electrons which can be transferred from that body to another. It should be noted that charges don’t get transported in fractions. Therefore, the overall charge on a body is simply an integral multiple of charge on an electron.
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1. What is the definition of electric charge? |
2. What are the types of electric charges? |
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