Electric Charge and Static Electricity (pages 34 41) Electric Charge (page 35) Key Concept: Charges that are the same repel each other. Charges that are different attract each other. Electric charge is a property of protons and electrons. Protons have a positive charge. Electrons have a negative charge. Two charges that are the same push away from each other. Two charges that are different pull toward each other. If a proton and an electron come close together, they attract each other. Attraction (pull) and repulsion (push) between electric charges is known as interaction between charges. The interaction between charges is called electricity. 1. Circle the letter of each sentence that is true about electric charge. a. Two charges that are different pull toward each other. b. Electrons have a negative charge. c. If a proton and an electron come close together, they repel each other. 2. The interaction between charges is called. 16
Electric Force (page 36) Key Concept: An electric field is a region around a charged object where the object s electric force is exerted on other charged objects. Electric force is the attraction or repulsion between electric charges. A magnetic field surrounds a charged object. An electric field is a region around a charged object in which electric force occurs. Suppose one charged object is placed in the electric field of a second charged object. The first charged object is either pushed or pulled repelled or attracted. The strength of an electric field depends on how far away the charged object is. The farther away a charged object is, the weaker the electric field is. Electricity 3. Complete the table about the force around charged objects. Force Around a Charged Object Term Electric a. Description the attraction or repulsion between electric charges Electric b. a region around a charged object in which electric force occurs 17
4. The farther away a charged object is, the the electric field is. Static Electricity (page 37) Key Concept: In static electricity, charges build up on an object, but they do not flow continuously. Most objects usually have no charge. However, objects can become charged. If an object loses electrons, it has more protons than electrons. Therefore, it has a positive charge. If an object gains electrons, it has more electrons than protons. Therefore, it has a negative charge. Static electricity is the buildup of charges on an object. Static means not moving. In static electricity, the charges do not flow or move. 5. The buildup of charges on an object is called electricity. 6. Is the following sentence true or false? If an object gains electrons, it will have a positive charge. Transferring Charge (pages 38 40) Key Concept: There are three methods by which charges can be transferred to build up static electricity: charging by friction, by conduction, and by induction. An object becomes charged when electrons move from one place to another place. 18
Charging by friction is when electrons move from one uncharged object to another object by rubbing. For example, a girl charges by friction when she rubs her socks on the carpet. Charging by conduction is when electrons move from a charged object to another object by direct contact. You can charge yourself by conduction when you touch a charged object. Charging by induction is when electrons move to one part of an object due to the electric field of another object. There is no touching in charging by induction. You can find out if an object is charged by using an instrument called an electroscope. ideas on page 18 and above. 7. Read each word in the box. In each sentence below, fill in one of the words. induction friction conduction static a. Charging by is when electrons move from a charged object to another object by direct contact. b. Charging by is when electrons move from one uncharged object to another object by rubbing. c. Charging by is when electrons move to one part of an object due to the electric field of another object. 19
8. Which method of transferring charges is shown in the picture below? Static Discharge (pages 40 41) Key Concept: When a negatively charged object and a positively charged object are brought together, electrons transfer until both objects have the same charge. Charges may build up as static electricity on an object. But the charges do not stay on that object forever. The loss of static electricity as charges move from one object to another is called static discharge. A static discharge often produces a spark. For example, there may be a tiny spark when you touch a metal doorknob. Lightning is another example of static discharge. 9. The loss of static electricity as charges move from one object to another is called. 10. Is the following sentence true or false? Thunder is an example of static discharge. 20