Electrical Circuits

Colegio Panamericano 2016-17 – 2nd Semester

Name: ___________________________________

Physics 12 – Electric circuits

Date: __________________

__________________________________________________________________________________________________ Learning Objectives: 1. Determine the effective resistance of a number of resistors connected in series and in parallel. 2. Write and apply equations involving voltage, current, and resistance for a circuit containing resistors connected in series and in parallel. QUESTIONS Q1. In a simple battery-and-bulb circuit, is the electric current that enters the bulb on the side nearer to the positive terminal of the battery larger than the current that leaves the bulb on the opposite side? Explain. Q2. Are electric current and electric charge the same thing? Explain. Q3. If we decrease the potential difference across a resistance in a circuit, will the current flowing through that resistance increase, remain the same, or decrease? Explain.

Q9. When current passes through a series combination of resistors, does the current get smaller as it goes through each successive resistor in the combination? Explain. Q10. In the circuit shown, the circle with a V in it represents a voltmeter. Which of the following statements is correct? Explain. a. The voltmeter is in the correct position for measuring the voltage difference across R. b. No current will flow through the meter, so it will have no effect. c. The meter will draw a large current.

Q4. A dead battery will still indicate a voltage when a good voltmeter is connected across the terminals. Can the battery still be used to light a light bulb? Explain. Q5. Two resistors are connected in series with a battery as shown in the diagram. R1 is less than R2.

a. Which of the two resistors, if either, has the greater current flowing through it? Explain. b. Which of the two resistors, if either, has the greatest voltage difference across it? Explain. Q6. In the circuit shown below, R1, R2, and R3 are three resistors of different values. R3 is greater than R2, and R2 is greater than R1. ɛ is the electromotive force of the battery whose internal resistance is negligible. Which of the three resistors has the greatest current flowing through it? Explain.

Q11. In the circuit shown, the circle with an A in it represents an ammeter. Which of these statements is correct? Comment on each. a. The meter is in the correct position for measuring the current through R. b. No current will flow through the meter, so it will have no effect. c. The meter will draw a significant current from the battery.

Q12. Is electric energy the same as electric power? Explain. Q13. If the current through a certain resistance is doubled, does the power dissipated in that resistor also double? Explain. Q14. Does the power being delivered by a battery depend on the resistance of the circuit connected to the battery? Explain.

EXERCISES E1. A charge of 30 C passes at a steady rate through a resistor in a time of 5 s. What is the current through the resistor? E2. A current of 2.5 A flows through a battery for 1 min. How much charge passes through the battery in that time? Q7. In the circuit shown in question 14, which of the three resistors, if any, has the largest voltage difference across it? Explain. *Q8. If we disconnect R2 from the rest of the circuit shown in the diagram for question 14, will the current through R3 increase, decrease, or remain the same? Explain.

E3. A 24-Ω resistor in a circuit has a voltage difference of 6 V across its leads. What is the current through this resistor? E4. A current of 1.5 A is flowing through a resistance of 18 Ω. What is the voltage difference across this resistance? E5. A current of 0.6 A flows through a resistor with a voltage difference of 120 V across it. What is the resistance of this resistor?

E6. Three resistors are connected to a 6-V battery as shown. The internal resistance of the battery is negligible. a. What is the current through the 15- Ω resistance? b. Does this same current flow through the 25- Ω resistance? c. What is the voltage difference across the 20- Ω resistance?

E7. Three identical resistances, each 24 Ω are connected in parallel with one another as shown. The combination is connected to a 12-V battery whose internal resistance is negligible. a. What is the equivalent resistance of this parallel combination? b. What is the total current through the combination? c. How much current flows through each resistor in the combination?

E8. A 9-V battery in a simple circuit produces a current of1.5 A through the circuit. How much power is being delivered by the battery? E9. A 30- Ω resistor has a voltage difference of 3 V across its leads. a. What is the current through the resistor? b. What is the power being dissipated in this resistor? E10. A toaster draws a current of 7 A when it is connected to a 110-V ac line. a. What is the power consumption of this toaster? b. What is the resistance of the heating element in the toaster?

SYNTHESIS PROBLEM SP1. In the circuit shown, the internal resistance of the battery can be considered negligible. a. What is the equivalent resistance of the two-resistor parallel combination? b. What is the total current flowing through the battery? c. What is the current flowing through the 6-Ω resistor? d. What is the power dissipated in the 8-Ω resistor? e. Is the current flowing through the 8-Ω resistor greater or less than that flowing through the 6-Ω resistor? Explain.