CLASS-12th Subjective Question
Ch-1 Electric Charge And Fields
Q.1. Define electric charge and write its S.I. unit ?
Ans:- charge is a physical fundamental quantity. S.I. unit of charge is coulomb (C).
Q.2. What is Coulomb’s law ?
Ans:- Coulomb’s law is that force between two charges is directly proportional to the product of charges and inversely proportional to the square of separation between them.
Q.3. Define electric field intensity. write its SI unit and dimensional formula.
Ans:- Electric field is the region around a charge in which other charges experiences force. S.I. unit of electric field is N/C. Dimensional formula of electric field is [MLT⁻³A⁻¹]
Q.4. What is electric field lines ?
Ans:- Electric field lines is an imaginary line tangent to which gives the direction of electric field. Two electric field lines never intersect each other.
Q.5. Write two properties of electric lines of force.
Ans:- (i) In electrostatic condition electric field lines never form closed loops.
(ii) Electric field lines are always perpendicular to the surface of conductor and equipotential surface.
Q.6. Define electric flux. Write its S.I. units ?
Ans:- Electric flux simply means number of electric field lines crossing through a surface. S.I. unit of electric flux is Nm²/C. or volt-meter.
Q.7. Define electric dipole moment (p) and write its S.I. unit ?
Ans:- Electric dipole is the combination of two charges having equal magnitude, opposite polarity and kept at very small separation. Dipole moment is a vector quantity. SI unit of electric dipole moment is C×m.
Q.8. What do you mean by conductors and insulators ?
Ans:- Conductors have large number of free electrons,called good conductor. Example- Silver,copper,human body,earth, etc. Net electric field inside conductor is always zero in electrostatic condition.
Those material having there is deficiency of free electrons is called insulators. Example- Ebonite, quartz, mica, sulpher, glass, wax, etc.
Q.9. What are limitations of Coulomb’s law ?
Ans:- Limitations of Coulomb’s law:- (i) It is applicable for point charges only. (ii) The distance between particles should not be too large.
Q.10. What do you mean by surface charge density ? Write its SI unit .
Ans:- The charge per unit area of a surface is known as surface charge density. If a charge Q be uniformly distributed in an area A of surface , the surface charge density σ is given by, σ = Q/A
The SI unit surface charge density is ”coulomb per square meter.” (Cm⁻²).