IMPORTANT TERMS . DEFINITION AND FORMULAE
1. Electric and magnetic force determines the properties of atoms . molecules and bulk matter
2 From simple experiments on frictional electricity ; one can inter that there are two types of charge in nature and that the like charge repel and unlike charge attract . By correction , the charge on a glass rod rubbed with silk is positive that one a plastic rod rubbed with fur is then negative .
3. Conductors allow large scale movement of electric charge through them . insulators do not in metals , the mobile charges are electrons ; in electrolytes both positive and negative ions are mobile .
4. Electric charge has three basic properties : quantisation , additivity and conservation . Quantisation of electric charge means that total charge ( q ) of a body is always an integral multiple of a basic quantum of charge ( e ) Le .. q = # e , where n = 0 , -1,2,3 , .. . Proton and electron have charges + e , -e , respectively . For macroscopic charges for which n is a very large number , quantisation of charge can be igonred . Additivity of electric charge means that the total charge of system is the algebraic sum ( i.e. , the sum taking into account proper signs ) of all individual charge in the system . Conservation of electric charge means that the total charge of an isolated system remains uncharged with time . This means that when bodies are charged through friction , there is a transfer of electric charge from one body to another , but no creation or destuction of charge .
5. Coulomb's Law : The mutual electrostatic force between two point charges q , and q , is proportional to the product qq , and inversely proportional to the square of the distance r , separating them Mathematically : King ) , F - force on 4 , due to ₁ - 2 1 where r , is a unit vector in the direction from q ; to q , and k = is the constant of proportionality . In S1 units , the unit of charge is coulomb . The experimental value of the constante , is = 8.854 x 10 - ¹2 C²Nm²² The approximate value of k is k- 9 x 10 " N m²C²
6. The ratio of electric force and gravitational force between a proton and an electron is
7. Superposition Principle : The principle is based on the property that the forces with which two charges attract on repel each other are not affected by the presence of a third ( or more ) additional charge ( s ) . For an assembly of charges q₁ . 92.4 the force on any charge , say qis the vector sum of the force on q , due to q ,, the force on q , due toq , and so on . For each pair , the force is given by the Coulomb's law for two charges stated earlier . = 2.4 x 10 "39
8. The electric field E at a point due to a charge configuration is the force on a small positive test charge q placed at the point divided by the magnitude of the charge . Electric field due to a point charge q has a magnitude 1q | / 4ne , r , it is radially outwards from qif qis positive and radially inwards irq is negative . Like Coulomb force , electric field also satisfies superposition principle.
9. An electric field line is a curve drawn in such a way that the tangent at each point on the curve gives the direction of electric field at that point . The relative closeness of field lines indicates the relative strength of electric field at different points . They crowd near each other in regions of strong electric field and are apart where the electric field is weak . In regions of constant electric field lines are parallel straight lines .
10 Some of the important properties of field lines are :
( a ) Field lines are continuous curves without any breaks . ( b ) Two field lines cannot cross each other , ( c ) Electrostatic field lines start at positive charges and end at negative charges they cannot form closed loops
1. Define the term electric dipole moment . Is it a scalar or a vector quantity ? Ans . The magnitude of dipole momast is equal to the product of either charge and the distance between the charge . It is a vector quantity
2. Define the term electric flux . Write its SI units . Ans . Electric flux through an area is the product of magritude of area and the component of electric field vector normal to it .
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