Tiêu đề 01.Electric charge and fields-f.pdf ✅

Physics Smart Booklet 1 1.ELECTRIC CHARGES AND FIELDS Physics Smart Booklet Theory + NCERT MCQs + Topic Wise Practice MCQs + NEET PYQs Content Writer 7905239992
Physics Smart Booklet 2
Physics Smart Booklet 3 Electric Charges and Fields Charge and its properties • Charge, like mass is a basic property of matter. • Charges are of two types − the one on proton, by convention is named positive and the other an electron, by convention is named negative. A neutron has no net charge and is electrically neutral. Fundamental properties of charges (a) Charge is conserved − quantity the net of charge in an isolated system remains constant. (b) Charge is quantized − the charge on any particle is an integral multiple of a fundamental unit of charge e, namely the charge on an electron or proton. Q ne =  : n = 1, 2, 3 ... where 19 e 1.6 10 C − =  . Protons and neutrons are made up of quarks with fractional values of e. However, quarks do not occur in free state. (c) Charge is invariant − unlike mass, length and time, charge on a body is independent of its state of motion (reference frames). (d) Charge is a scalar and is additive. (e) Like charges repel and unlike charges attract. Auxillary properties of electric charge (i) An electric charge in motion produces a magnetic field in addition to the electric field. (ii) An accelerated charge radiates energy in the form of electromagnetic waves. Methods of charging a body Bodies can be charged by • Friction (E.g. rubbing of glass with wool etc.) The two bodies acquire opposite kind of charge, due to one body losing electrons to other body. • Conduction (E.g. bringing an uncharged body in contact with a charged body) During conduction, the body getting charged acquires part of the charge from the source (charging body). • Induction (E.g. bringing a uncharged body near a charged body) During induction, the body getting charged acquires opposite kind of charge on its surface close to the charging body. The net charge on the charged body is still zero. However, by earthing, the charged body can be made to retain one type of charge. The charge on the source body remains intact. This method is applicable to only conductors. • irradiating a conducting body by suitable electromagnetic radiation • heating a body to a high temperature • by applying a large electric field • In all the above methods the body regains electrical neutrality over a period of time. • Whether a body is charged or not and if charged, the type and extent of charge can be detected by a device called electroscope. The amount of charge on a body can be measured by a device called electrometer. Coulomb’s law: The force (F) of attraction or repulsion between two point charges is directly proportional to the product of the charges (Q1 and Q2) and inversely proportional to the square of the distance (r) between them. 1 2 2 Q Q F r   1 2 2 0 1 Q Q F 4 r =  where 9 2 2 0 1 9 10 Nm C 4 − =   0 is called the permittivity of free space and 0 = 8.854  10−12 C 2 N −1 m −2