* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Relationship Between Current, Voltage, and Resistance
Survey
Document related concepts
Flexible electronics wikipedia , lookup
Regenerative circuit wikipedia , lookup
Crystal radio wikipedia , lookup
Telecommunications engineering wikipedia , lookup
Galvanometer wikipedia , lookup
Lumped element model wikipedia , lookup
Index of electronics articles wikipedia , lookup
Current source wikipedia , lookup
Current mirror wikipedia , lookup
Electrical ballast wikipedia , lookup
Surface-mount technology wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
RLC circuit wikipedia , lookup
Transcript
Relationship Between Current, Voltage, And Resistance In A Circuit Topic Ohm’s Law Introduction Ohm’s Law states that the current flowing through a conductor is proportional to the potential difference between its ends (provided the temperature of the conductor remains constant). In this experiment, you will illustrate Ohm’s Law by measuring how the potential difference (in volts) measured across a conductor varies when the current (measured in amps) in the circuit changes. You will change the current in the circuit by changing the resistance of the circuit. This can be done either by connecting a rheostat in the circuit and varying its setting, or by connecting resistors of different values in the circuit. Time required 30 minutes Materials 3 × 1.5 volt D batteries in holders knife switch (single pole, single throw type) 5 ohm resistor (0.25 watts) rheostat (a variable resistor) 9 clip leads small piece of aluminum foil (about 5 cm square) ammeter voltmeter calculator The appearance of the components may vary among suppliers (see Appendix A for website addresses of possible suppliers). Diagram 1 below shows the symbols used in the circuit diagram given in this experiment to show the arrangement of the components. 1 positive pole negative pole cell variable resistor switch resistor A V ammeter voltmeter Symbols used in circuit diagram © Diagram Visual Information Ltd. Published by Facts On File, Inc. All electronic storage, reproduction, or transmittal is copyright protected by the publisher. Safety note Do not use an electrical outlet. Procedure 1. Secure the resistor (the “conductor”) between two clip leads. If necessary, tear off a piece of aluminum foil and wrap it around the wire end of the resistor to make a more secure connection. 2. Arrange the equipment as shown in diagram 2 below. Close the switch. Record the readings on the voltmeter and ammeter in the data table below in the row labeled “reading 1.” 3. Open the switch. Move the slider on the rheostat to vary its resistance. Close the switch. Record the readings on the voltmeter and ammeter in the data table in the row labeled “reading 2.” 4. Repeat step 3 three more times to give readings 3 – 5 in the data table. 5. For each set of readings, divide the value obtained for V by the value obtained for I. Record the result in the right-hand column of the data table. 2A ammeter 2B + – total 4.5V clip leads ~5 ohm resistor clip lead A V voltmeter R switch rheostat Circuit used to illustrate Ohm’s Law: wiring diagram (A) and circuit diagram (B) © Diagram Visual Information Ltd. Published by Facts On File, Inc. All electronic storage, reproduction, or transmittal is copyright protected by the publisher. DATA Reading TABLE Voltmeter reading (volts) Ammeter reading (amps) V I V I 1 2 3 4 5 Analysis 1. What can you say about the ratio V/I calculated in the data table above? Want to know more? Click here to view our findings. © Diagram Visual Information Ltd. Published by Facts On File, Inc. All electronic storage, reproduction, or transmittal is copyright protected by the publisher. 10.33 • OUR FINDINGS PHYSICS EXPERIMENTS ON FILETM The total resistance of conductors connected in parallel (R) is given by: 1= 1 1 1 + + R R1 R2 R3 Resistors are used in this experiment rather than light bulbs because the wire in a light bulb heats up when it is lit. This increases its resistance. 7.07 Relationship Between Current, Voltage, and Resistance In A Circuit 1. The ratio of the potential difference measured across the conductor to the current in the circuit is the same for each reading. This illustrates Ohm’s Law, which states that, at constant temperature, the potential difference (V, measured in volts) across a conductor divided by the current through it (I, measured in amps) is constant and is equal to the resistance of the conductor (measured in ohms). This is usually written as: R=V I Therefore, the resistance of the conductor is given in the right-hand column of the data table. 7.08 Hot Wires Part A: Electric heating of wire 1. The wire glowed a brighter red at higher voltages. At higher voltages, a larger current passed through the wire. This caused the wire to increase in temperature and emit a brighter color. A light bulb uses the heating effect of electricity. If you look at a light bulb, the filament at the center is the part that glows with a bright white light when the bulb is lit. The filament is a very fine coil of wire. This wire is far thinner than the wire used in the experiment, and it reaches very high temperatures when electricity passes through it. The wavelength of radiation emitted from a hot object depends on its temperature (see Experiment 5.03: Dark And Dull Or Bright And Shiny?). The light emitted by the bulb is composed of much shorter wavelengths than the red light emitted by the heated wire in Part A; the wire making up the filament of the bulb is much hotter than the wire in this experiment. Part B: Using a fuse 1. The fuse consists of a very fine length of wire inside a transparent tube with metal connectors at each end. 2. The wire in the tube quickly became red and then separated into two pieces. The wire became dark again. It becomes dark as it cools down. © Diagram Visual Information Ltd. Published by Facts On File, Inc. All electronic storage, reproduction, or transmittal is copyright protected by the publisher.