Unit 8 Circuits Review Key

Name: Key Date: Period: Unit 8 Review - Circuits Essential Skills that will be tested 8-1: Student can identify all of the variables and their units for this unit (V, I, R, P,   E, Q) 8-2: Students know how to solve for current, voltage, or resistance using concepts of current and Ohm's Law. 8-3: Students can calculate the power (rate of energy dissipation) or energy dissipated in any resistor by using the formula P   = IV or P = E/t. 8-4: Student can draw and complete a VIR chart for a series circuit. 8-5: Student can draw and complete a VIR chart for a parallel circuit. 8-16: Student can build a series/parallel circuit and find its equivalent resistance. Questions: (this is only a partial review - use your worksheets, notes, & labs for more!) 1. Fill in the following table information. | Variable Name | Variable Symbol | SI Unit Name | Unit Symbol | SI Unit in disguise | Formula | On Reference Sheet? | |---|---|---|---|---|---|---| | Charge | Q | Coulomb | C | N/A | N/A | no | | Power | P | Watt | W | Joule per Second (J/s) | P = IV or P = E/t | yes & no | | Electric Potential Difference/Voltage | V | Volt | V | Joule per Coulomb (J/C) | V = IR or V = E/q | yes & no | | Current | I | Amp | A | Coulomb per Second (C/s) | I = Q/t or I = V/R | yes | | Resistance | R | Ohm | Ω | N/A | R = V/I or R = ρL/A | no | | Energy | E | Joule | J or kWh | N/A | E = Pt | no 2. What do you need in order for charges to move? An electric potential difference 3. What is produced when charges are moving? A current 4. What two requirements must be met in order for something to be considered a circuit? 1) closed   loop 2) conducting materials 5. Which of the following are true of an electric circuit? Circle all that apply. a. Electrons are the mobile charge carriers in an electric circuit. b. The path of charge flow from the   + to the - terminal of the circuit can consist of nonconductive materials.   c. Charge is supplied with energy in the internal circuit (battery) and the energy is transformed into other forms in the external circuit. d. Charge is consumed as it moves through the energy-transforming devices of the external circuit. For instance, the amount of charge entering a light bulb in a second is less than that which exits the light bulb in a second.   e. A battery is used to power a flashlight circuit. When the battery no longer works, it is because it has run out of charge.   f. The location on an electric circuit where the charge possesses the greatest amount of electric potential energy is the + terminal of the battery.   6. Which of the following are true about electric potential or electric potential difference? Circle all that apply. a. Electric potential can be expressed in units of volts. b. Electric potential can also be expressed   in units of joules. c. The electric potential of a charge at a given location provides a measure of the rate at which charge flows past that point. d. Work must be done on a charge to move it against (i.e., in the opposite direction of) an electric field. e. As a charge moves in the same direction as an electric field, it gains electric potential. f. The electric potential difference between two points is simply the difference in potential energy possessed by charge between those two points. g. If a unit of charge has a high electric potential at any given location, then that charge possesses a large amount of electric potential energy at that location. h. The + terminal of a battery is a location with a higher electric potential than the - terminal of a battery. i. Charge flowing through a battery will experience a gain in electric potential. j. A 6-Volt battery would provide 12 Joules of energy to 2 Coulombs of charge as it is moved from the - to the + terminal.   7. Which of the following are true about electric current? Circle all that apply. a. Electric current is measured in units of Amperes. b. Electric current is defined as the number of Coulombs of charge which move past a point on a circuit   per unit of time. c. Electric current provides a measure of how fast charge moves between two points on a circuit. d. Electric current is equal to the number of Coulombs of charge which move between two points on a circuit. e. The electric current in a circuit will increase as the electric potential impressed across a circuit is increased. f. Suppose a miniature light bulb is connected to a battery in a circuit. A light bulb with a greater resistance will have a greater current.   g. Wider conducting wires are capable of carrying larger currents. 8. Which of the following statements are true about an electric resistance? List all that apply. a. The resistance of an electric   circuit is a measure of the overall amount of hindrance to the flow of charge through the circuit. b. A large resistance value indicates that the charge is encountering a relatively large amount of difficulty in moving through the circuit. c. The unit of resistance is the Ampere. d. A 5-ohm resistor would allow a current of 0.5 Amperes when 2.5 Volts is impressed across it. e. A 10-ohm resistor would allow a current of 2 Amperes when 5 Volts is impressed across it. f. The resistance of a conducting wire will increase as the length of the wire is increased. g. The resistance of a conducting wire will increase as the cross-sectional area of the wire is increased. h. Increasing the resistance of an electric circuit will cause the current in the circuit to increase. i. A threefold increase in the resistance of an electric circuit will result in a threefold decrease in the electric current. j. A miniature light bulb with a specific resistance is connected to a 1.5-Volt battery to form a circuit. If it were connected to a 6-Volt battery instead, its resistance would increase by a factor of   4. 9. Which of the following statements are true about electric power and electric potential energy? List all that apply. a. Power is the amount of energy used by an electrical appliance. b. Power is the rate at which energy is used by an electric circuit. c. A kilowatt-hour is a unit of electric power. d. A Joule/second is a unit of power. e. A 60-Watt light bulb would consume 30 Joules of electrical energy in 2 seconds. f. A 120-Watt light bulb would consume 1200 Joules of electrical energy in 6 seconds. g. A charge moving through an electric circuit would gain electric potential energy in the   battery and lose electric potential energy in the external circuit. h. Charge has the greatest amount of electric potential energy at the + terminal of the battery. i. If a 60-Watt light bulb is placed in a 120-Volt circuit, then the current in the light bulb is 2 Amps. j. Consider two light bulbs with different power ratings   plugged into the same power supply (separately, not in series). A 60-Watt light bulb has a greater resistance than a 100-Watt light bulb.   10. Which of the following statements are true about a series circuit? List all that apply. a. Series circuits are characterized by the fact that there is a single pathway by which charge can travel from the + terminal to the - terminal. b. During any single loop of charge around a series circuit, the charge will pass through each resistor in the circuit. c. The overall resistance of a circuit increases as more and more resistors are placed in series in the circuit. d. The total current in a circuit increases as more and more resistors are placed in series in the circuit. e. Suppose that three identical resistors with a resistance of 3-ohms are placed in series with a 12-Volt battery. The current in the circuit is 4 Amps. f. Suppose that three identical resistors with a resistance of 3-ohms are placed in series with a 12-Volt battery. The electric potential difference across each resistor is 12 Volts. g. Suppose that two identical resistors are placed in series with a 12-Volt battery. The current in the circuit is 6 Amps. The resistance of each resistor is 4 ohms.   11. Which of the following statements are true about a parallel circuit? List all that apply. a. Parallel circuits are characterized by the fact that there are multiple pathways by which charge can travel from the + terminal to the - terminal. b. During any single loop of charge around a parallel circuit, the charge will pass through each resistor in the circuit. c. The overall resistance of a circuit increases as more and more resistors are placed in parallel in the circuit. d. The total current in a circuit increases as more and more resistors are placed in parallel in the circuit. e. Suppose that three identical resistors with a resistance of 3-ohms are placed in parallel with a 12-Volt battery. The current in the circuit is 1 Amp. f. Suppose that three identical resistors with a resistance of 3-ohms are placed in parallel with a 12-Volt battery. The electric potential difference across each resistor is 12 Volts.   12. The potential energy possessed per unit of charge at any given location is referred to as the electric **potential**. 13. A 12-Volt battery would supply: * 2 Coulombs of charge with 12 Joules of energy * 12 Coulombs of charge with 1 Joule of energy * 0.5 Coulombs of charge with 24 Joules of energy * 24 Coulombs of charge with 0.5 Joules of energy 14. One Ampere is the amount of current that exists when one **Coulomb** flows by a certain point in a conductor in one **second**. 15. If 6 Coulombs of charge flow past point 'A' in a circuit in 4 seconds, then ____ Coulombs of charge flow past point 'A' in 8 seconds.   12 16. What are the 3 roles of a battery in a circuit? 1) provide energy 2) provide a potential difference 3) pump charge from - to + terminal 17. Draw in the direction of conventional current. Explain why you illustrated the current in this direction below. [Image of a circuit with a battery and a light bulb] Conventional current is the direction of a + charge around the circuit. 18. The current through the battery is: * greater than that through the light bulb * less than that through the light bulb * the same as that through the light bulb 19. Where are the charges most energized? at the + terminal 20. Where do the charges that flow through the wires in your home originate? in the wires/devices in your home 21. When a battery is "recharged", what is actually happening in the battery? chemical reactions The electric circuit shown at the right consists of a battery and three identical light bulbs. Use this diagram to answer the next two questions. 23. Which of the following are true of the current in this circuit?   * The current through point X will be greater than that through point Z. * The current through point Z will be greater than that through point Y. * The current will be the same through points X, Y, and Z. * The current through point X will be greater than that through point Y. * The current through point Y will be greater than that through point X.   24. Which of the following are true of the voltages in this circuit?   * The electric potential difference between X and Y is more than that between Y and Z. * The electric potential difference between   X and W is more than that between Y and W. * The electric potential difference between X and Y is the same as that between Y and Z. * The electric potential difference between X and   W is the same as that between Y and W. * The electric potential difference between Y and W is more than that between X and Y.   25. A high voltage battery can: * do a lot of work on each charge it encounters. * push a lot of charge through a circuit. * do a lot of work over the course of its lifetime. * last a long time. 26. When a light bulb has burned out, what has happened? filament has broken, opening the circuit. 27. The resistance of a charge-carrying conducting wire will increase as the: Choose all that apply. * length of the wire is increased * cross-sectional area of the wire is increased * temperature of the wire is increased * voltage impressed across the ends of the wire is increased * wire is placed closer and closer to the terminal of the circuit