Important for board exam

 

Q1. Repulsion is the sure test for electrification. Explain

Attraction can exist between a charged body and uncharged body as well as between bodies having opposite charges. However, repulsion will only take place between bodies having similar charges. Hence, repulsion is the sure test for electrification.

Q2. what are the differences between electrostatic forces and gravitational forces ?

• Gravitational forces are always attractive but electrostatics forces may be attractive or repulsive.
• gravitational forces are independent of nature of medium but electrostatics forces are depends on medium.
• Electrostatics forces are large as compared to the gravitational forces.
• Electrostatics forces operate over small distances. However gravitational forces operate over large distances.

Q3. what are the properties of charge?

1. Charge is a scalar quantity. They can be added  algebraically.
2. Charge can be transferred from one body to another.
3. Charges cannot exist without mass, through mass can exist without net charge.
4. Charge can neither be created nor destroyed, so that the total charge of an isolated system is always conserved.
5. The charge on body does not change with its speed, so it is independent of the frame of reference. 
6.  Charge is quantized i.e charge on a body is integral multiple of basic charge (Charge on 1 electron)

                                Q = ± ne, Where  n = 1,2,3,………

                                                e = 1.6 x 10^-19 C      

Q4. what do you mean by conservation of electric charge?

The law of conservation of electric charge states that for an isolated system, the total charge always remains constant. charges can neither be created nor be destroyed.

Q5. what do you mean by quantization of charge?

Quantization of charge means, charge on a body is integral multiple of basic charge (Charge on 1 electron)

                             i.e   Q = ± ne, Where  n = 1,2,3,………

                                                e = 1.6 x 10^-19 C      

Q6. what are the limitation of Coulomb's Law?

• It holds for point charge only.
• It holds for stationary charge only

Q7. Define relative permittivity or Dielectric Constant.

Dielectric constant of the medium is the ratio of absolute permittivity of the medium to the electrical permittivity of the free space. 

                            ε_r or K = ε/ε₀ 

Q8. what are the properties of electric field lines.

1. Electric field lines comes out of positive charge and go into the negative charge.

2. Tangent to the field lines at any point gives the direction of the field at that point.

3. No two electric field lines of force can intersect each other. This is because at the point of intersection, we can draw two tangent. This would mean two direction of electric field intensity at the same point, which is not possible.

4. Fields line are always normal to conducting surface.

5. Field lines do not exist inside a conductor.

6. The electric field lines never form closed loop.

7. If the lines of force are equidistant and parallel straight lines, the field is uniform and if either , lines of force are not equidistant or straight line or both, the field will be non uniform.

8. The density of field lines is proportional to the strength of electric field.  

Q9. No two electric field lines can intersect each other. why?

In case the the two field lines intersect each other at a point, then two tangent can drawn at that point. This would mean two directions of electric field at that point which is not possible.    

Q10. what is an electric dipole ?

A system of two equal and opposite point charges separated by a small distance is called an electric dipole.

Q11. what is electric dipole moment ?

Dipole moment is a measure of the strength of electric dipole. Dipole moment is equal to the product of the magnitude of either charge and the distance between them.

it is a vector quantity.

Unit - Coulomb-meter (C-m)

Dimension - [ITL]

Q12. Can two equipotential surface intersect each other ?

No, two equipotential surface can not intersect each other. If two equipotential surface intersect each other, it means that electric field at that point of intersection has two directions which is not possible.

Q13. what is Gaussian Surface ?

It is a hypothetical close surface drawn in the electric filed to find the surface of field intensity so that Gauss's law can be applied.

Q14. what is electron volt (eV) ?

It is the energy acquired by an electron when accelerated through a potential difference of 1 volt.

                             1 eV = 1.6 X 10 ^-19 J

Q15. what is an equipotential surface ?

Any surface over which electric potential is the same at every point is called an equipotential surface.

Q16. what is electric flux ?

The electric flux through a given area in an electric field represents the total number of electric lines o force crossing the area.

                            Electric flux 

it is a scalar quantity.

Unit - Nm²/C

Dimension -[ ML³T^-3A^-1 ]                                   

Q17. State gauss's law in electrostatics.

Gauss's law state that the total electric flux passing through a closed surface is equal to 1/ε₀ times the net charge enclosed by the closed surface.

                                            φ = 1/ε₀ q_net

Q18. State superposition principle for electric field intensity.

According to superposition principle, the electric field intensity at a point due to a system of charges is the vector sum of the electric fields at the point due to individual charges.

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