68 Voltage and Current in Simple Circuits (Voltage Sensor, Current Sensor) E&M: Voltage and current Equipment List DataStudio file: 68 Simple Circuits.ds Qty Items Part Numbers 1 PASCO interface (for two sensors) (see note) 1 Voltage Sensor( see note) CI-6503 1 Current Sensor (see note) CI-6556 1 AC/DC Electronics Lab EM-8656 2 D cell 1.5 volt Note: You will not use the PASCO interface, the voltage sensor or the current sensor for this lab; instead you will use the ammeter to measure current and voltmeter to measure voltages. Please remember that the current you are dealing with are the order of 1-2 A, so be sure to select the proper range to measure the current with the ammeter or else you will damage the device. Introduction The purpose of this activity is to explore what happens to the voltage and the current in a simple circuit composed of batteries and light bulbs arranged in series and then arranged in parallel. Use a voltage sensor, a current sensor, and the DataStudio software to measure the voltage across parts of the series and parallel circuits and a current sensor to measure the current through the circuits. Background Voltage is the ratio of electric potential energy to charge. One volt is one joule of energy per one coulomb of charge. Current is the volume of electric charge, or the number of charges per second moving past a point in an electric circuit. The unit for current is the ampere and one ampere is one coulomb of charge per second. In a simple circuit of a battery connected to a light bulb, the battery is a voltage source, and the light bulb is a load. Light bulbs in a series circuit are connected end-to-end like links in a chain bracelet. Imagine a circuit with one light bulb in it. What would happen to the brightness of the light bulb if a second light bulb were added in series to the first light bulb? What would happen to the voltage across each individual bulb as more and more bulbs are added in series to the circuit? What would happen to the current through the circuit as more and more bulbs are added in series to the circuit? Light bulbs in a parallel circuit are connected side-by-side like rung in a stepladder. Again imagine a circuit with one light in it. What would happen to the brightness of the light bulb if a second light bulb were added in parallel to the first light bulb? What would happen to the voltage across each individual bulb as more bulbs are added in parallel to the circuit? What would happen to the current through the circuit as more and more bulbs are added in parallel to the circuit? PASCO 2004 68-1 of 7
68 Voltage and Current Physics Experiment Manual 012-09286 Prediction 1. If one bulb in a series circuit is removed, what happens to the rest of the bulbs? 2. If one bulb in a parallel circuit of many bulbs is removed, what happens to the rest of the bulbs? SAFETY REMINDER Follow directions for using the equipment. Setup 1. Set up the PASCO interface and computer and start DataStudio. Connect the Voltage Sensor and the Current Sensor into the interface. 2. Open the DataStudio file: 68 Simple Circuits.ds The file opens with Digits displays of voltage and current. The voltage Digits display will show the voltage across whatever part of the circuit you select. The current Digits display will show the current through the circuit. 3. Insert two D cell batteries into the AC/DC Electronics Laboratory board. 4. Use wire leads to build up a circuit with the two D cells, the pushbutton switch, the Current Sensor, and bulb A as shown. 5. Clip the leads of the Voltage Sensor to the positive and negative terminals of the battery holders as shown. Note: The diagram is not to scale and doesn t show the connections to the PASCO interface. Bulb A Pushbutton switch 68-2 of 7 2004 PASCO
012-09286 Physics Experiment Manual 68 Voltage and Current Procedure 1 voltage and current for bulbs in series Note: Data recording is easier if one person runs the computer and records data, a second person presses the pushbutton switch, and a third person handles the Voltage Sensor leads. One Bulb 1. Begin measuring data. Select Monitor from the Experiment menu in DataStudio. 2. Press and hold the pushbutton switch. Observe bulb A and the Digits displays of Voltage and Current. 3. Record the values of voltage across the voltage source (D cells) and current through the circuit in the Lab Report section. 4. Move the Voltage Sensor leads to the spring clips on either side of bulb A and record the voltage across the light bulb. 5. Release the pushbutton switch. Two Bulbs in Series 6. Change the circuit to add bulb B in series. Move the wire lead from the negative terminal of the battery holder to the spring clip below bulb B. Add a wire lead from the spring clip below bulb A to the spring clip above bulb B as shown. 7. Press and hold the pushbutton switch. 8. Record the values of voltage across the voltage source (D cells) and current through the circuit with two bulbs in series. 9. Move the Voltage Sensor leads to the spring clips on either side of bulb A and record the voltage across bulb A as before. 10. Move the Voltage Sensor leads to the spring clips on either side of bulb B and record the voltage across bulb B. 11. Move the sensor leads so one is on the clip above bulb A and the other is on the clip below bulb B and record the voltage across both bulbs. 12. Release the pushbutton switch. Add a Move a across 2 bulbs. PASCO 2004 68-3 of 7
68 Voltage and Current Physics Experiment Manual 012-09286 Three Bulbs in Series 13. Change the circuit to add bulb C in series. Move the wire lead from the negative terminal of the battery holder to the spring clip below bulb C. Add a wire lead from the spring clip below bulb B to the spring clip above bulb C as shown. 14. Press and hold the pushbutton switch. 15. Record the values of voltage across the voltage source (D cells) and current through the circuit with three bulbs in series. Add a Move a 16. Move the Voltage Sensor leads to the spring clips on either side of bulb A and record the voltage across bulb A as before. Move the leads and measure the voltage across bulb B. Move the leads and measure the voltage across bulb C. 17. Next, move the sensor leads so one is on the spring clip above bulb A and the other is on the spring clip below bulb C and record the voltage across three bulbs. 18. Finally, unscrew any one of the three bulbs and record what happens to the other two bulbs. Screw the bulb back into its socket. 19. Release the pushbutton switch. across 3 bulbs. 68-4 of 7 2004 PASCO
012-09286 Physics Experiment Manual 68 Voltage and Current Procedure 2 voltage and current for bulbs in parallel Two Bulbs in Parallel 1. Return the AC/DC Electronics Laboratory board to the way it was at the beginning of Procedure 1. The measurements of voltage and current for one bulb in parallel are the same as the measurements for one bulb in series. 2. Change the circuit to add bulb B in parallel to bulb A. Add a wire lead from the spring clip above bulb A to the spring clip above bulb B as shown. Add a second wire lead from the spring clip below bulb A to the spring clip below bulb B. 3. Press and hold the pushbutton switch. 4. Record the values of voltage across the voltage source (D cells) and current through the circuit with two bulbs in parallel. 5. Move the Voltage Sensor leads to the spring clips on either side of bulb B and record the voltage across bulb B as before. 6. Release the pushbutton switch. Three Bulbs in Parallel 7. Change the circuit to add bulb C in parallel to the other bulbs. Add a wire lead from the spring clip above bulb B to the spring clip above bulb C. Add a second wire lead from the spring clip below bulb B to the spring clip below bulb C. 8. Press and hold the pushbutton switch. 9. Record the values of voltage across the voltage source (D cells) and current through the circuit with three bulbs in parallel. 10. Move the Voltage Sensor leads to the spring clips on either side of bulb B and record the voltage across bulb B as before. Move the leads to the spring clips on either side of bulb C and record the voltage across bulb C. 11. Finally, unscrew any one of the three bulbs and record what happens to the other two bulbs. Screw the bulb back into its socket. 12. Release the pushbutton switch. Click Stop in DataStudio. Add a across B. across C. PASCO 2004 68-5 of 7
68 Voltage and Current Physics Experiment Manual 012-09286 Lab Report: Voltage and Current in Simple Circuits Prediction 1. If one bulb in a series circuit of many bulbs is removed, what happens to the rest of the bulbs? 2. If one bulb in a parallel circuit of many bulbs is removed, what happens to the rest of the bulbs? Data Procedure 1: Voltage and Current for Bulbs in Series Item One Bulb Voltage across voltage source Value V Current through circuit: A Procedure 2: Voltage and Current for Voltage across bulb A V Bulbs in Parallel Two Bulbs in Series Two Bulbs in Parallel Item Value Item Value Voltage across voltage source V Voltage across voltage source V Current through circuit: A Current through circuit: A Voltage across bulb A V Voltage across bulb A V Voltage across bulb B V Voltage across bulb B V Voltage across A and B V Voltage across A and B V Three Bulbs in Series Three Bulbs in Parallel Item Value Item Value Voltage across voltage source V Voltage across voltage source V Current through circuit: A Current through circuit: A Voltage across bulb A V Voltage across bulb A V Voltage across bulb B V Voltage across bulb B V Voltage across bulb C V Voltage across bulb C V Voltage across A to C V Voltage across A to C V What happens in the series circuit of three bulbs if one bulb is removed? What happens in the parallel circuit of three bulbs if one bulb is removed? 68-6 of 7 2004 PASCO
012-09999 Physics Experiment Manual 68 Voltage and Current Analysis Questions 1. What happens to the voltage across the voltage source change as more light bulbs are added in a series circuit? 2. How did your calculated (theoretical) value for current through the resistors in series compare to the actual (measured) value for current? 3. What happens to the current through a series circuit change as more light bulbs are added in series? 4. How did your calculated (theoretical) value for current through the resistors compare to the actual (measured) value for current? 5. What happens to the voltage across the voltage source change as more light bulbs are added in a parallel circuit? 6. What happens to the voltages across the light bulbs in a parallel circuit change as more light bulbs are added to the circuit? 7. What happens to the current through a parallel circuit change as more light bulbs are added in parallel? 8. What happens to the brightness of each bulb in a parallel circuit as more bulbs are added? PASCO 2004 68-7 of 7