Chapter 9 Review

1. List and describe each of the 3 ways in which objects become electrically charged. 1) Charging by Friction 2) Charging by Contact 3) Induction

2. What is the law of electric charges? Opposite charges will attract each other and like charges will repel.

3. Which particles in the atom move when electric charge is transferred from one atom to another? Electrons

4. With the aid of a diagram, demonstrate why a balloon will stick to a wall. Label charges before and after friction.

5. Explain the purpose of the electrostatic series. Describe a practical example to illustrate your answer. The electrostatic series is used to show how tightly an object holds onto it’s electrons. We can tell which objects like to become positive, and which will become negative. For example, rub a balloon in your hair. The balloon will become negative and your hair would become positive. (Hair is higher on the electrostatic series then rubber).

6. You would like to create the strongest negative charge possible on a plastic bag. Which would you rub it with: a wool sock or a cotton cloth? Explain. You would rub it with a wool sock because wool is further from plastic on the electrostatic series.

7. Why do bounce sheets work so effectively at reducing static buildup? The molecules of the softener transfer to the fabrics and make the different materials appear more like one another. When the materials are alike, they do not create charge buildup when they rub against each other.

8. What happens when a negatively charged object touches an electroscope? Draw a diagram.

9. If a positively charged object is brought near part A of a neutral electroscope, will the electrons move to the top of the electroscope, or the bottom? Explain.

10. Define insulator and conductor and give an example of each. Insulator- a substance in which electrons cannot move freely from atom to atom Examples: wood, rubber, glass, air Conductor- a substance in which electrons can move freely from atom to atom. Examples: copper, gold, iron, mercury

11. Explain why an electric charge quickly builds up on the surface of furniture when it is being polished, but not on water taps. Wooden furniture is an insulator. When it is rubbed, the charges build up and then do not move. Water taps are made of metal, a conductor. The charges move from the water taps, to the pipes, and into the ground.

12. Why do we cover some conductors with insulators – 2 reasons. 1) To protect us from electric shocks 2) To prevent wires from crossing

13) Electrons will not transfer freely through insulators. Give three examples of insulators from the electrostatic series. 1) rubber 2) plastic 3) glass

14. Why is static electricity not a problem in summer? In summer, the air is more humid. Water molecules in the air tend to pick up charges and transfer them more easily. Therefore, charges do not build up as much.

15. List the three ways to discharge an object. 1) Grounding 2) Discharge at a point 3) By water

16. Define discharging. How does a static wick on an airplane help to discharge electrons? Discharging- to neutralize or remove all electric charges A static wick ends in a point. Electrons will easily repel each other off of pointed objects.

17. How does induction work? When a neutral object comes close to a charged object, the charged object causes the charges in the neutral object to shift position slightly. The neutral object then has an opposite charge induced on the surface closest to the charged object.

18. The bottom of a thundercloud has what charge? Negative

18. How does a lightning rod protect a building? (2 ways) 1) They help prevent lightning from striking. They are positively charged and push positive ions up into thunderclouds, neutralizing them. 2) If lightning strikes, they direct the charge through the conductor, to the ground.

19. Why does lightning strike tall objects? The electric charges flow in a series of steps to find the easiest path to the ground. The tallest objects shorten the path to the ground, especially if they are made of metal conductors.

20. Why is lightning sometimes jagged and not a straight line? The jagged path is caused by the electric charges moving along the path of least resistance in the air.