# Unit 9 Extra Credit

Either print this page and complete or (better yet) neatly show your answers on a separate page of paper. All answers must be expressed as complete sentences and/or all work shown to receive credit.

1. Describe the conditions which are necessary for a sustained flow of electric charge through a conducting medium.

2. Will current flow through a wire when one end is connected to a battery terminal and the other end is remaining free? Explain.

3. Carefully distinguish between an open circuit and a closed circuit.

4. Distinguish between an ampere and a volt.

5. What effect does doubling both the voltage and the current have upon the resistance of an electric circuit? Assume the circuit obeys Ohm's law.

6. Why are thick wires rather than thin wires used to carry large currents?

7. Will a lamp with a thin or a thick filament draw the most current?

8. Why do wires heat up when they carry electric current?

9. Why will too much current cause a light bulb to burn out?

10. Would the resistance of a 100-Watt bulb be greater than or less than the resistance of a 60-Watt bulb?

11. Which bulb in the preceding exercise has the thicker filament?

12. Which will do the least damage: plugging an appliance rated at 110-Volts into a 220-Volt circuit, or plugging an appliance rated at 220-Volts into a 110-Volt circuit? Explain.

13. If a current of one- or two-tenths of an ampere flows into your hand and out the other hand, you will probably be electrocuted. But if the current flows into your hand and out the elbow above the same hand, you will probably survive (though the current may be large enough to burn your flesh). Explain.

14. Why is the wingspan of birds a consideration in determining spacing between parallel wires in a power line?

15. If several light bulbs are wired in series, a single burned-out bulb will disrupt the entire circuit. However, if the light bulbs are wired in parallel, a single burned-out bulb does not disrupt the circuit. Explain the difference.

16. When a light bulb in a series circuit burns out, how is the current affected?

17. When a light bulb in a parallel circuit burns out, how is the current affected?

18. How is the current in a series circuit affected when one or more electrical devices are added? Explain why.

19. How is the current in a parallel circuit affected when one or more electrical devices are added? Explain why.

20. In some of the older low-cost sets of Christmas-tree lights, one burned-out bulb would result in the inability of all the bulbs to light. Postulate why?

21. Explain why household appliances are almost never connected in series.

22. Explain why household appliances are almost never connected in series.

23. A 60-Watt and a 100-Watt bulb are connected in parallel in a circuit. Which bulb will experience the greatest current flow?

24. A 60-Watt and a 100-Watt bulb are connected in series in a circuit. Which bulb will experience the greatest voltage drop?

25. A 60-Watt and a 100-Watt bulb are connected in parallel in a circuit. Which bulb will experience the greatest voltage drop?

26. Why will too many electrical devices operated at one time often blow a fuse?

27. Some people will substitute a copper penny for a blown safety fuse in order to restore an electric circuit. Explain why this is not a wise idea.

Resources for physics students are available through links on the GBS Physics Home Page. Such resources include the Multimedia Physics Studios (a collection of animations and movies which illustrate key physics concepts) and The Physics Classroom (an online tutorial written in an easy-to-understand language).

This page created by Suzanne Webb of Glenbrook South High School.

Comments and suggestions can be sent by e-mail to Suzanne Webb.