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Let's be clear about this. The slope DOES NOT give you the resistance. The resistance is defined to be V/I, not dV/dI, although these two things happen to be the same for an ohmic resistor.
Reference: https://www.physicsforums.com/threads/which-is-the-resistance-1-slope-or-v-i-in-i-v-graph.73312/
Introduction
In a conductor of electricity, the electric current flow through it is directly proportional to the potential difference applied across it. The ratio of potential difference (p.d.) V to current I is called the resistance R and this relationship, known as Ohm's law is shown in the PhET simulation below.
Ohm's Law Experimentation
Ohm's Law Experimentation
If the ratio of p.d. to current is constant over a wide range of p.d.s, then the material is said to be an "ohmic" material. If the ratio is not constant then the material is said to be a "non-ohmic" material.
In this experiment you will investigate ohmic and non-ohmic behaviour by measuring how current varies with p.d. across a resistor and a light bulb filament.
Apparatus
power supply, potentiometer, 3-resistors (red, green, blue), lamp, voltage probe, current probe, LabQuest, connecting leads
The potentiometer (sometimes known as a rheostat) is a type of variable resistor that can be used to set the potential difference of the power supply to any value between 0 and its maximum value. The circuit symbol for the potentiometer is shown below along with a photograph to help identify which sockets to connect in the circuit.
Or using the PhET simulation, set up the circuit as shown in the gif below. Adjusting the resistance of the resistor / light bulb you will accomplish the same as the potentiometer. Please experiment with the various settings prior to data collection.
Part A - Constant Resistor (red, green, blue and bulb)
Classroom Setup:
Using the setup as shown in class,
Select one of the colored resistors, adjust the voltage on the Power Supply (limit of 0 - 5V). Repeat this 4-5x to obtain a variety of data points.
Measure the current through the resistor from the ammeter and the p.d. across it from the voltmeter.
Repeat with the other two colors of resistors and the bulb.
Use an appropriate format (graph your data) to show the relationship between the potential difference and the current for each specific resistor.
The complete data can be found HERE.
Ratio v. Gradient:
Ratio v. Gradient:
There is a significant emphasis on the nature of the relationship between the Voltage and Current in an Ohmic resistor. The function relating the voltage and current in a simple circuit is a discrete function. The physical nature of the relationship indicates that 'Ohm's Law' only holds true for a small range of values on specific resistors, therefore it is non-predictive in nature, unless specified as Ohmic.
The slope DOES NOT give you the resistance. The resistance is defined to be V/I, not dV/dI, although these two things happen to be the same for an ohmic resistor.
Reference: https://www.physicsforums.com/threads/which-is-the-resistance-1-slope-or-v-i-in-i-v-graph.73312/
Part B - Constant Voltage
Set up the circuit using the dial potentiometer (as shown in the pic)
Set the voltage on the Power Supply (do not change this value.
Using the multimeter, measure the resistance of the potentiometer.
Using the EVENTS WITH ENTRY mode on the LabQuest, record the current and resistance for 4 different voltages.
Measure the current through the lamp from the ammeter (Vernier Current Sensor) and the p.d. across it from the voltmeter (Vernier Potential Probe).
Use an appropriate format (graph of your data) to show the relationship between the potential difference and the current for a lamp.
The complete data can be found HERE.
A possible question may be to describe the significance of the coefficient of the x value (0.847, etc) and the importance of the exponent on each of the sets of data.
Using the raw data, this is a good opportunity to practice linearizing data and interpreting a linearized graph.
Two of the most famous and most commonly used equations in an introductory physics class are below, describing the relationship between force, mass and acceleration and Voltage, Current and Resistance.
However, both relationships are written in non-intuitive formats (formats that are easier to print in early textbooks). Experimentally, acceleration and current can only be measured as a result of varying the other two variables in their respective equations. Resulting in equations below:
Relationships can now be read and interpreted in the same way: the Force and Voltage can be considered driving agents. While the mass and resistance are both variables that inhibit the motion of the mass or charges.
Current at switch on
Connect the circuit shown below with a current sensor in series with a lamp, switch and battery.
With the switch open and the lamp OFF set the current sensor to zero (using the zeroing function).
Set the Data Collection Rate to 20 samples/s and Duration: to 10.0 s
Click on the Collect data button and close the switch. Observe the current -time graph.
Explain the shape of the graph.
Replace the lamp with a fixed value resistor and compare the current in the resistor at switch on with the current in the lamp at switch on.
Power Dissipation
Power Dissipation
Potential Difference Units:
Potential Difference Units:
The units for potential difference (V) (or Voltage) is shown below. Potential difference (Volt) is the amount of energy per charge (J/C).
Current Units:
Current Units:
The units for Current (I) is measured in Amperes or Amps (A). This is a measurement of the charges passing a point in a given time (C/s). It is a rate.
Power Units:
Power Units:
Power is measured in Watts or Joules per second. Show that P=IV is the electrical equation for power.
Energy Measurement (kWh)
Energy Measurement (kWh)
An electric company doesn't care how quickly you use power (unless there are brown-outs or surges in usage), they are more concerned with the amount of ENERGY you use within a given time.
Some additional Resources:
Some additional Resources:
billy_bobby_and_bo_lecture_notes_for_chapter_19-1.pdfbilly_bobby_and_bo_lecture_notes_for_chapter_19-2.pdf
Discussion Questions
Discussion Questions
A light-rail commuter train draws 630 A of 650-V DC electricity when accelerating. (a) What is its power consumption rate in kilowatts? (b) How long does it take to reach 20.0 m/s starting from rest if its loaded mass is 5.30×10^4 kg, assuming 95.0% efficiency and constant power? (c) Find its average acceleration. (d) Discuss how the acceleration you found for the light-rail train compares to what might be typical for an automobile.
2. An old lightbulb draws only 50.0 W, rather than its original 60.0 W, due to evaporative thinning of its filament. By what factor is its diameter reduced, assuming uniform thinning along its length? Neglect any effects caused by temperature differences.
3. The average television is said to be on 6 hours per day. Estimate the yearly cost of electricity to operate 100 million TVs, assuming their power consumption averages 150 W and the cost of electricity averages 12.0 cents/kW⋅h.
4. Alkaline batteries have the advantage of putting out constant voltage until very nearly the end of their life. How long will an alkaline battery rated at 1.00 A⋅h and 1.58 V keep a 1.00-W flashlight bulb burning?
5. Show that the units 1 A^2⋅Ω=1 W, as implied by the equation P=I^2R.
6. Show that the units 1 V^2/Ω=1 W, as implied by the equation P=V^2/R.
7. Verify the energy unit equivalence that 1 kW⋅h = 3.60×10^6 J.
Ohm's Law and Complex Circuits
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