Electric Forces - Electric Charge

Question 1

electric charge

Answer 1

• In earlier units, we learned about different types of forces, like gravity, friction, and normal force. In this unit, we learn about a different kind of force, caused by electric charges.
• Electric charge is a property that objects can have, like mass. There are two different types of charge, positive (+) and negative (-). Electric charges exert forces on other electric charges: positive and negative charges attract each other, while charges of similar sign repel each other.
• Electric charges originate within the atoms of matter. Atoms are constructed of three basic “sub-atomic” particles: protons, neutrons, and electrons. Protons have a positive electric charge; electrons have the same amount of charge as a proton, but it is negative; and neutrons have no charge. The protons and neutrons are located in a bundle at the center of the atom, called the “nucleus.” The nucleus therefore has all the positive charge in the atom. Around it fly a number of tiny electrons with negative charge. In normal atoms, there are an equal number of positive protons and negative electrons, which makes the total charge on an atom zero. However, it is not too difficult to knock off one or two of the electrons. Those electrons can be transferred to another object, giving that object an overall negative charge. The atom that lost the electrons now has more protons than electrons, leaving it with an overall positive charge.
• So, though objects are usually uncharged, it is possible to “charge them up” by transferring electrons from one object to another. The object that gains electrons becomes negatively charged; the object that lost electrons becomes positively charge. You may notice this in the winter when your socks rub across the carpet; you rub some electrons off the carpet and become negatively charged, so when you touch a doorknob, you shock yourself.
• The symbol for electric charge is “q”. The unit for charge in the metric system is the Coulomb, C. The amount of charge on a proton or electron is much, much less than a Coulomb. We call the charge on a proton “e”.
• e = 1.60*10-19 C.
• Protons have a charge of +e. Electrons have a charge of –e.