Chapter 20 Assessment 393q15

Alex Willis 8th Physical Science, 4th Hour May 10, 2011

Chapter 20 Assessment

1. A material has a net electric charge because it  C. An excess or shortage of electrons. 2. Static electricity is the study of  A. Buildup of charges. 3. A strong electric field is  A directed toward a charge 4. What is a material called that easily carries a current?  D. Conductor 5. A superconducting material  C. has no resistance at low temperatures 6. What does Ohm’s law state?  D. Voltage equals current times resistance. 7. Which melts to protect a circuit?  D. Fuse 8. What does “I” represent in the equation P=I*V?  C. Current 9. The output of a diode can be  A. Direct current 10. Three layers of semiconductor material can form  A. A transistor only 11. How does the electric force between two charged objects change if you double the distance between the objects?  The electric force decreases.

12. What determines the direction of the electric field near a charge?  The direction of the force on a positive charge 13. How can a charged object cause charges to move within an uncharged object?  The charged object can charge the uncharged object through friction, , or induction. 14. If the current in a circuit is clockwise, what is the direction of electron flow? 

Counterclockwise

15. Explain why a wire becomes warmer when charges flow through it.  The collision of electrons creates thermal energy. 16. Does voltage flow in a circuit? Explain.  No, voltage is the measurement of potential difference in an electric field. 17. Does the same current through each bulb? Explain why or why not.  Yes, There is only one battery. 18. What happens to the other bulbs if bulb A burns our? If bulb B burns out?  If bulb A burns out, nothing will happen to bulbs B or C; but if bulb B goes out, bulb C will also go out while bulb A will stay lit. 19. A battery and a light bulb are connected in a simple circuit. What is the source of electrons that flow through the wire?  The battery. 20. Explain why a light bulb does not change its brightness when another bulb is added in a parallel.  The charge in a parallel circuit has more than one route in the circuit. The circuit to the first bulb does not change.

21. What are digital and analog signals?  Digital signals encode information as a string of 1’s and 0’s. Analog signals are varying signals produced by continuously changing the strength or frequency of the signal.