Static cling generated in a clothes dryer and the attraction of straw to recently polished amber also result from rubbing. Similarly, lightning results from air movements under certain weather conditions. You can also rub a balloon on your hair, and the static electricity created can then make the balloon cling to a wall. We also have to be cautious of static electricity, especially in dry climates.
When we pump gasoline, we are warned to discharge ourselves after sliding across the seat on a metal surface before grabbing the gas nozzle.
Attendants in hospital operating rooms must wear booties with aluminum foil on the bottoms to avoid creating sparks which may ignite the oxygen being used. How do we know there are two types of electric charge? When various materials are rubbed together in controlled ways, certain combinations of materials always produce one type of charge on one material and the opposite type on the other.
Since the glass and silk have opposite charges, they attract one another like clothes that have rubbed together in a dryer. Two glass rods rubbed with silk in this manner will repel one another, since each rod has positive charge on it. Similarly, two silk cloths so rubbed will repel, since both cloths have negative charge.
Figure 2 shows how these simple materials can be used to explore the nature of the force between charges. Figure 2. A glass rod becomes positively charged when rubbed with silk, while the silk becomes negatively charged. More sophisticated questions arise. Where do these charges come from? Can you create or destroy charge? Is there a smallest unit of charge? Exactly how does the force depend on the amount of charge and the distance between charges? Such questions obviously occurred to Benjamin Franklin and other early researchers, and they interest us even today.
Franklin wrote in his letters and books that he could see the effects of electric charge but did not understand what caused the phenomenon.
Today we have the advantage of knowing that normal matter is made of atoms, and that atoms contain positive and negative charges, usually in equal amounts. Figure 3. This simplified and not to scale view of an atom is called the planetary model of the atom. Negative electrons orbit a much heavier positive nucleus, as the planets orbit the much heavier sun.
There the similarity ends, because forces in the atom are electromagnetic, whereas those in the planetary system are gravitational. Normal macroscopic amounts of matter contain immense numbers of atoms and molecules and, hence, even greater numbers of individual negative and positive charges.
Figure 3 shows a simple model of an atom with negative electrons orbiting its positive nucleus. The nucleus is positive due to the presence of positively charged protons.
Nearly all charge in nature is due to electrons and protons, which are two of the three building blocks of most matter. The third is the neutron, which is neutral, carrying no charge. Other charge-carrying particles are observed in cosmic rays and nuclear decay, and are created in particle accelerators. All but the electron and proton survive only a short time and are quite rare by comparison.
The charges of electrons and protons are identical in magnitude but opposite in sign. Furthermore, all charged objects in nature are integral multiples of this basic quantity of charge, meaning that all charges are made of combinations of a basic unit of charge. Usually, charges are formed by combinations of electrons and protons.
The magnitude of this basic charge is. The symbol q is commonly used for charge and the subscript e indicates the charge of a single electron or proton. The SI unit of charge is the coulomb C. The number of protons needed to make a charge of 1. Similarly, 6. Just as there is a smallest bit of an element an atom , there is a smallest bit of charge. Physical Quantities and Measurement. Force and Pressure. Light Energy. Heat Transfer. Objective Questions - I.
Objective Questions - II. Q20 A glass rod is rubbed with silk. Explain the charging of the glass rod and the silk on the basis of electron movement. When a glass rod is rubbed with silk, glass rod loses electrons and silk gains electrons. Glass rod becomes positively charged and silk becomes negatively charged. For example, suppose a glass rod has 10 protons and 10 electrons and silk has 7 electrons and 7 protons.
On rubbing together, the glass rod loses 2 electrons and silk gains 2 electrons. Now the glass rod has 8 electrons and 10 protons which makes it positively charged. So when the glass rod is rubbed with wool, it loses electrons as per its macroscopic properties, and gets positively charged, while the wool gains those electrons and gets negatively charged. Rubbing the glass rod with the silk makes it lose electrons, so glass rod becomes positively charged.
When a negatively charged ebonite rod is brought near the glass rod it attract each other as unlike charges attract each other. When an ebonite rod rubbed with fur it acquires negative charge and when glass rod is rubbed with silk cloth it acquires positive charge. Therefore, they will attract. The rubbed part of the balloon now has a negative charge.
Objects made of rubber, such as the balloon, are electrical insulators, meaning that they resist electric charges flowing through them. When the balloon has been rubbed enough times to gain a sufficient negative charge, it will be attracted to the wall. Begin typing your search term above and press enter to search. Press ESC to cancel. Skip to content Home Physics Why does a glass rod become positively charge when it is rubbed with a silk cloth?
Ben Davis December 1, Why does a glass rod become positively charge when it is rubbed with a silk cloth? When a glass rod is stroked with a piece of silk?
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