## Thursday, November 22, 2012

### Properties of Electric Lines of Force or Field Lines

1. The electric lines of force are imaginary lines.
2. A unit positive charge placed in the electric field tends to follow a path along the field line if it is free to do
so.

3. The electric lines of force emanate from a positive charge and terminate on a negative charge.

4. The tangent to an electric field line at any point gives the direction of the electric field at that point.

5. Two electric lines of force can never cross each other. If they do, then at the point of intersection, there
will be two tangents. It means there are two values of the electric field at that point, which is not possible.
Further, electric field being a vector quantity, there can be only one resultant field at the given point,
represented by one tangent at the given point for the given line of force.

6. Electric lines of force are closer (crowded) where the electric field is stronger and the lines spread
out where the electric field is weaker.

7. Electric lines of force are perpendicular to the surface of a positively or negatively charged body.

8. Electric lines of force contract lengthwise to represent attraction between two unlike charges.

9. Electric lines of force exert lateral (sideways) pressure to represent repulsion between two like charges.

10.The number of lines per unit cross – sectional area perpendicular to the field lines (i.e. density of lines of
force) is directly proportional to the magnitude of the intensity of electric field in that region.

11. Electric lines of force do not pass through a conductor. Hence, the interior of the conductor is free from
the influence of the electric field.

12. Electric lines of force can pass through an insulator.
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Some of these questions which may be asked in your Board Examination 2012-2013

Q1: what are the characteristic of charges acquired by the objects on rubbing against each other?

Q2: Who suggested first that there are two kinds of charges?

Q3: How can you show that there are two types of charges?

Q4: An ebonite rod is rubbed with the fur or wool. What type of charges do they acquire?

Q5Is mass of body affected on charging?

Q6: What is the polarity of charge?

1. thnxs its is so useful for me

2. i agree with dhana lakshmi

2. what are super conductors?

1. A superconductor is a special type of material that conducts electricity without resistance. That means that electrons (tiny particles with negative charge) can flow very easily through the material. This can be achieved only at very low temperatures. The temperature at which a material becomes superconducting varies from material to material. Not all materials are superconductors.

2. materials with zero resistance

3. suuuuuthooo

3. it is too gud
as it helps mee in undrstnd all about tht
so thanks

4. what is electric flux?

1. Hi Ashutosh,

http://dmr-physicsnotes.blogspot.in/2012/11/electric-flux.html

5. wat does the 7th property mean

6. Why r electric field lines normal to the surface while entering /leaving? Please explain point 8&9

7. thank you sir,
is dere any difference between e-field and e- field intensity

1. Electric field is the region around an electric charge upto which a electrostatic force due to it can be experienced.
electric field intensity is the strength of electric field lines.

8. Hi Misha,

Yes, e-field is the area where electric filed lines are present. e-field intensity is, how strong are the electric field lines.

Regards
DMR

9. Plz tell me more about points 8th nd 9th..... What they mean??

1. It explains attraction betwwen unlike charges and repulsion between like charges.

10. Q.6 ans. The property of charge that differentiates two kinds of charges is polarity of charge.

11. for points 8 and 9 ,

Consider that electric field is not normal to the surface.we can resolve electric field into its two rectangular components ,

(a) E perpendicular i.e. perpendicular to the surface and
(b) E parallel i.e. along the surface

As the sphere is a charged conductor so E parallel experiences some force due to the charges .
Thus, it has to move away But due to electrostatic force it does not allow E parallel to move away.
this is why Electric field is perpendicular.

12. So did u find my answers convinient which i posted yesterday.

13. What is the principle of a capacitor?
Dharmendra kumar,will you help me out with this?

14. Benjamin Franklin

15. Benjamin Franklin

16. hindi m ni h kya???

17. Yeah its too useful for the learners as well..well done..

18. Why field lines donot form closed loop??

19. Why field lines donot form closed loop??

20. What will happen to the electric lines of force if we have 2 unlike charged bars with decreasing charge density from down to top??........will they be crowded at the bottom an apart towards top...???

21. Give two properties of electric lines of force. Sketch them for an isolated positive point charge and an electric dipole.

22. What are the 4 important properties of electric field lines?