PHY 102 RS Electricityand Magnetism Exercises PDF

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Terri Golden PHY-102: Electricity and Magnetism Exercises Complete the following exercises. 1. Why are good conductors of heat also good conductors of electricity? Answer: Both heat and electricity need number of free electrons for travelling from one end of a metal to another. This is the reason why good conductors of heat are also good conductors of electricity. Charge and heat is transferred because of the presence of these free charge particles.

2. What is the difference between a good conductor and a good insulator? Answer: There are no free electrons in insulators, for good insulators electrons are closely bind together because of strong molecular forces. While in good conductors there are large number of free electrons or charge carriers.

3. Which of the following are conductors? (Select all that apply) A. Wood B. Copper C. Gold D. Plastic E. Distilled water Answer: Copper, Gold 4. Which of the following are insulators? (Select all that apply) A. Wood B. Copper C. Gold D. Plastic E. Distilled water Answer: Wood, Plastic, Distilled water. 5. A nail contains trillions of electrons. Given that electrons repel from each other; why do they not then fly out of the nail? © 2014. Grand Canyon University. All Rights Reserved.

Answer: Yes, a nail contains trillions of electrons that repel each other, but in meantime there is also a nucleus for every atom containing protons that have opposite charge of electron. So, protons attract electrons more strongly than the repulsion force between the electrons. Free electrons are bind together because of force attraction between them and the nucleus at the center of the atom. 6. How do the number of electrons flowing into a light bulb compare to the number of electrons flowing out of it? Answer: To have the net current or effect equal to zero the number of flowing electrons in one direction equals to the number electrons in the opposite direction. The free electrons leave the positive charges behind which are repelled by the negative terminal of the battery producing a non-conventional current in opposite direction. 7. A light bulb connected to a 9-V battery has a current of 1.5 A flowing. a. Find the resistance of the light bulb (in ohms) b. Find the power drawn by the light bulb (in W) A. Answer: V = I*R R = V/I R = 9/1.5 R = 6 ohm B. Answer: P = V*I P = 9*1.5 P = 13.5 W

8. Consider three identical light bulbs connected as shown in the circuit below.

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a. Which light bulb(s) will be brightest? Explain. b. What will happen to B and C if light bulb A is removed? Explain. c. What will happen to A and B if light bulb C is removed? Explain. A. Answer: Bulb A will be the brightest among all of the three. Because in parallel voltage is same while it divides in series. So, the voltage across A will be equal to the combined voltage across B and C. B. Answer: Removing A will not have any effect on B and C. C. Answer: A and B would become dimmer, but after some both will maintain the same brightness again. The reason is having greater resistance will reduce the current keeping the voltage constant. 9. Rank the following from smallest current to largest current. A. A 1200W microwave connected to 110V outlet. B. A 1500W water heater connected to 220V outlet. C. A 100W light bulb connected to 110V outlet. D. A 2000W oven connected to a 220V outlet. E. A 40W Light bulb connected to a 12V battery. Answer: 1. A 100W light bulb connected to 110V outlet. 2. 3. 4. 5.

A 40W Light bulb connected to a 12V battery. A 1500W water heater connected to 220V outlet. A 2000W oven connected to a 220V outlet. A 1200W microwave connected to 110V outlet. © 2014. Grand Canyon University. All Rights Reserved.

10. Your friend says an appliance uses energy. How would you correct his statement? Answer: Energy cannot be created or destroyed, energy is conserved and converted from on form to another. Same is the case for appliances, appliances do not consume energy they actually transform it from one form to another. Energy is usually converted into heat energy. 11. Describe the differences and similarities between an electromotor and a generator. Answer: The similarity is both use electricity but the direction is opposite. The difference between electromotor and generator is electromotor convert electrical energy into mechanical. While generator converts mechanical energy into electrical energy. 12. Your friend with great excitement tells you about his newest idea to solve the energy crisis: He wants to use an electromotor to drive a generator and then use part of the electric power generated to power the electromotor while using the rest to power his home. What would you tell him? Answer: This is totally impossible, because energy cannot be created from nowhere or destroyed. We can only transform it from one form of energy to another form. 13. Why is a paper clip attracted to a magnet, while is pencil is not? Answer: A paper clip is a metal with free electrons so in the presence of another magnet the metal itself becomes a magnet and attracted by the other. While, pencil is not a metal with and contains no free electrons. 14. A loop of wire embedded in the road at an intersection can be used to trigger a traffic signal. This is an application of magnetic induction. Explain. Answer: The changed flux in the loop produces or induces a current in the loop. This is how a loop wire embedded in the road at an intersection can be used to trigger a traffic signal. The remaining questions are multiple-choice questions:

15. Two like charges: A. Attract each other B. Repel each other C. Must be neutrons D. Neutralize each other Answer: Repel each other. © 2014. Grand Canyon University. All Rights Reserved.

16. When a plastic rod is rubbed with fur, the rod will become negatively charged. Which of the following best explains how this happens? A. Electrons are transferred from the plastic rod to the fur. B. Electrons are transferred from the fur to the plastic rod. C. Negative charges are created on the plastic rod. D. Positive charges are removed from the plastic rod. Answer: Electrons are transferred from the fur to the plastic rod. 17. What is characteristic of a good insulator? A. Electrons are usually not moving at all. B. Electrons are free to move around. C. Electrons are semi-free to move around. D. Electrons are tightly bound to the nuclei. Answer: Electrons are tightly bound to the nuclei. 18. In a solid conductor such as a metal, what is the cause of an electric current? A. A flow of positive and negative charges. B. A flow of positive charges only. C. A flow of negative charges only. D. A flow of protons. E. A flow of neutrons. Answer: A flow of negative charges only. 19. How does the resistance of a 100W light bulb compare to the resistance of a 60W light bulb? A. The 100W light bulb has a higher resistance than the 60W light bulb. B. The 100W light bulb has a lower resistance than the 60W light bulb. C. The 100W light bulb has the same resistance as the 60W light bulb. D. Not enough information to tell. Answer: The 100W light bulb has a lower resistance than the 60W light bulb. 20. Consider the five circuits in the diagram below.

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In which of the circuits will the light bulb light up? Answer: B. 21. What causes an electric field? A. A moving change only. B. A stationary charge only. C. Any charge, moving or stationary. D. A stationary magnet. Answer: Any charge, moving or stationary. 22. What causes a magnetic field? A. A moving change only. B. A stationary charge only. C. Any charge, moving or stationary. Answer: A moving charge only. 23. What does a step-up transformer do? A. It steps up the energy. B. It steps up the power. C. It steps up the voltage. D. It steps up the current. Answer: It steps up the voltage. 24. Which of the following is true for a generator? A. It transforms thermal energy to electrical energy. B. It transforms mechanical energy into electrical energy. C. It transforms electrical energy into mechanical energy. D. It transforms solar energy into electrical energy. Answer: It transforms mechanical energy into electrical energy. 25. Which of the following is true for an electromotor? © 2014. Grand Canyon University. All Rights Reserved.

A. B. C. D.

It transforms thermal energy to electrical energy. It transforms mechanical energy into electrical energy. It transforms electrical energy into mechanical energy. It transforms electrical energy into potential energy.

Answer: It transforms electrical energy into mechanical energy.

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