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Transcript

CHAPTER 3â€”ELECTRICITY TRUE/FALSE 1. As two electrical charges move further apart, the force between them decreases proportionally to the inverse square of their separation. ANS: T DIF: Medium 2. Electron flow and conventional current are equal in magnitude, yet opposite in direction. ANS: T DIF: Medium 3. Because the human body is an infinite supply of electric charges, it is used for the reference of ground. ANS: F DIF: Medium 4. The force between two charges is inversely proportional to the product of their magnitudes and directly proportional to the square of the distances between them. ANS: F DIF: Medium 5. Objects can be electrified by induction. ANS: T DIF: Easy 6. Induction is the process of electrical fields acting on one another with contact. ANS: F DIF: Easy 7. Electrons flow from greatest potential difference to least potential difference. ANS: T DIF: Easy 8. For potential difference to exist, there must be electron flow. ANS: F DIF: Medium 9. As the length of a conductor increases, the resistance increases. ANS: T DIF: Medium 10. The total resistance of a parallel circuit is always greater than the amount of the highest resistor. ANS: F DIF: Medium MULTIPLE CHOICE 1. The resistance in a wire decreases as its diameter ____. a. increases c. remains the same b. decreases d. none of the above ANS: A DIF: Medium 2. If the total resistance in a circuit is 9 ohms and the total voltage is 3 volts, the current is ____. a. 1/27 ampere c. 3 amperes b. 1/3 ampere d. 27 amperes ANS: B DIF: Medium 3. If a DC circuit is ____. a. in series, the currents are different for each component (e.g., resistors) b. in series, the voltages are the same for each component c. in parallel, the currents are equal for all paths of the circuit d. in parallel, the voltages are equal for all paths of the circuit ANS: D DIF: Medium 4. Current is ____. a. time/charge b. charge/time ANS: B c. (charge)(time) d. charge/time2 DIF: Easy 5. Coulomb's Law of electrical forces is mathematically described as ____. a. F = q1q2/r2 c. F = q1q2/r 2 b. F = q/r d. F = q2/r ANS: A DIF: Medium 6. A current of 2 amperes and a resistance of 8 ohms require what voltage in a circuit? a. 1/16 volt c. 4 volts b. 1/4 volt d. 16 volts ANS: D DIF: Medium 7. When an electric current flows through a wire with resistance, energy is ____. a. liberated as x-rays c. liberated as light b. liberated as heat d. absorbed as heat ANS: B DIF: Medium 8. Ohm's Law is mathematically described as ____. a. C = Q/V c. R = V/I b. L = -V/It d. V = I2R ANS: C DIF: Medium 9. Electric potential is measured in ____. a. coulombs b. joules ANS: C DIF: Easy 10. Electric insulators ____. a. convert electrical energy into heat b. consist of materials like silicon ANS: C c. volts d. ohms DIF: Medium c. inhibit movement of electrical charge d. permit movement of electrical charge 11. If 20 volts of potential difference causes a current of 5 amperes, the resistance produced is ____. a. 1/100 ohm c. 4 ohms b. 1/4 ohm d. 100 ohms ANS: C DIF: Medium 12. A volt is a measure of ____. a. random drift velocity b. flow rate ANS: D c. current d. potential difference DIF: Easy 13. A charge would lose most of its energy when it passes through a ____. a. resistor c. generator b. battery d. all of the above ANS: A DIF: Medium 14. If the distance between two electrical charges is doubled, the force between them is ____. a. decreased by 1/4 c. doubled b. decreased by 1/2 d. quadrupled ANS: A DIF: Medium 15. A formulation of power in a circuit with an EMF source and a resistor with a current is ____. a. P = IV c. P = I2R b. P = IR/V d. more than one of the above ANS: D DIF: Medium 16. An ampere is ____. a. coulomb/sec b. (coulomb)(sec) ANS: A c. (volt)(ohm) d. ohm/volt DIF: Easy 17. Resistance is ____. a. the opposition to the flow of electrons b. the opposition to the generation of electromotive force c. the location of storage of electrons d. measured in amperes ANS: A DIF: Easy 18. The charge on each of two objects is doubled and they are moved twice as far apart. The force between them is ____. a. increased by a factor of 4 c. increased by a factor of 1/2 b. increased by a factor of 2 d. unchanged ANS: D DIF: Medium 19. A circuit has a current of 2 amperes and a resistance of 4 ohms. The maximum power that can be delivered is ____. a. 16 watts c. 2 watts b. 8 watts d. 1/2 watt ANS: A DIF: Medium 20. The unit of electrical power is ____. a. joule b. volt ANS: D c. ampere d. watt DIF: Easy 21. If 10 coulombs pass a point in 2 seconds, the current is ____. a. 0.20 amp c. 20 amps b. 5 amps d. 200 amps ANS: B DIF: Medium 22. The electrons in an electrical current ____. a. all have the same velocity b. flow from one end of the circuit to another c. have a net motion in the direction opposite to the conventional current flow d. none of the above ANS: C DIF: Medium 23. In a battery circuit with several resistors of different values connected in series ____. a. the voltage drop is the same across all the resistors b. the current through each resistor is different c. the power dissipated through each resistor is the same d. none of the above ANS: D DIF: Difficult 24. If a conductor is positively charged, it ____. a. has too many electrons b. is deficient in electrons ANS: B DIF: Medium 25. The mA is a unit of ____. a. EMF b. voltage ANS: C c. has more neutrons than electrons d. is deficient in protons c. current d. potential difference DIF: Easy PROBLEM 1. If a circuit has potential difference of 80 kV and a current of 400 mA, what is the resistance? ANS: 2.0 × 105 ohms DIF: Difficult 2. A 100 watt light bulb operates on 120-volt household voltage. How much current does the light bulb draw? ANS: 0.83 amp DIF: Difficult 3. How much resistance does the bulb offer? ANS: 144.6 ohms DIF: Difficult 4. What is the total resistance of a circuit with two resistances of 3 and 5 ohms in series and two resistances of 4 ohms each in parallel? ANS: 10 ohms DIF: Difficult 5. Calculate the current supplied to a circuit with two resistances of 3 and 5 ohms in series and two resistances of 4 ohms each in parallel. ANS: 2 amperes DIF: Difficult