After a plastic comb is used for straightening dry hair (or rubbed on wool) it becomes electrically charged. The charge creates an electric field which then induces charge separation in nearby paper bits thus leading to a net electrostatic attractive force between the bits and the comb.
Try the following
- Rub your feet on a carpet and touch a doorknob. What happens?
- On a cold dry morning, have you ever felt that while removing a pullover, the hair on your hands stand up?
- Take a plastic comb and comb your hair quickly. (Your hair has to be dry). Take a few pieces of paper and hold the comb close to the papers. The papers will tend to get attached to the comb.
- Instead of a comb, try the same experiment using a glass rod. Rub the rod on a silk cloth, which will then get lifted towards the rod.
The main basis of electricity and magnetism is the electric charge. The charges tend to move so as to achieve an electrically neutral situation. Nature likes to be electrically neutral. A charge creates a region of influence that we call electric field. Charge, the electric field around it, and motion of charge, make up the entire branch of electricity and magnetism. To understand the basic concepts of electric charge, electric field and electric force, we will discuss very simple situations where the charges are stationary or when they move, they do not disturb the electrical field.
Experiences of electric charges in our everyday lives:
One of the best examples of observing effects of electric charges is lightning. It is one of nature’s spectacular offerings. Moisture bearing clouds are initially electrically neutral. But as the masses of clouds increase in size, they start rubbing against each other. Friction makes electrons jump, so that between two clouds there will be a charge imbalance - one cloud is positively charged and the second cloud is negatively charged.
When a positively charged cloud collides with a negatively charged cloud, charge neutralization occurs and sparks are produced. These sparks are seen as lightning. Sometimes the charge imbalance can occur between a cloud and the earth; lightning is seen when the charges are exchanged between the cloud and the earth.
What is making the paper stick to the comb or the glass rod? An easy interpretation of these observations is that some objects when rubbed acquire a property that we intuitively know to be charge. The paper piece also gets a charge imbalance due to presence of charged comb or rod.