## Thursday, March 23, 2017

### Electric force and Coulomb's Inverse square law Video Lesson

Electric force of attraction or repulsion exists between every two charges and it follows Coulomb's inverse square law. According to the law, the force between two charges is directly proportional to the product of charges and is inversely proportional to the square of the distance of separation.

Gravitational and electric forces are fundamental in nature. Gravitational force is due to mass of the particle and it exits between every two masses where as electric force exits between the the particles or bodies having only excess charges. Both of them obeys inverse square law but gravitational force is independent of medium but electric force depends on the medium between charges.

Gravitational force is the weakest of fundamental forces but electric force is much stronger than that. Gravitational force is further always attractive force but electric force is either attractive or repulsive. Further classification is explained in the video lesson below.

Coulomb's inverse square law

To identify the relation between the force and charges different experiments were conducted and we got to a conclusion that the electric force between the charges is directly proportional to the product of charges and is inversely proportional to the square of the distance of the separation.  The force also depends on the medium between the charges and its impact is studied basing on the permitivity of the medium. The ratio of permitivity of the medium to the permitivity of the free space is called dielectric constant or relative permitivity. Its value for the vacuum is one and for any non conducting medium it is greater than one. It is explained as shown in the video lesson below.

Effect of the medium on force between the charges

As we have explained earlier, we can understand that the force between the charges gets reduced when the medium is placed instead of the vacuum. It is further explained in the video lesson below. We can find out the effective distance in the presence of medium as shown below.

Impact of force between two charges when third charge is placed

Electric force between the charges is not effected even if we keep a new charge in between them. What makes a difference is, more forces are acting on each  charge and hence resultant force on each charge is more. But the force between two charges is not affected because of the third charge. To find the resultant charge, we can use vector laws of addition. It is explained in the video lesson below.

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