Lab5
TA: Keslo Estil SEC#: Name:
Lab. 5 Ohm’s Law & Resistance
The fundamental relationship among the three important electrical quantities current, voltage, and resistance was discovered by Georg Simon Ohm. The relationship and the unit of electrical resistance were both named for him to commemorate this contribution to physics. One statement of Ohm’s law is that the current through a resistor is proportional to the voltage across the resistor. In this experiment you will test the correctness of this law in several different circuits using a Current & Voltage Probe System and a computer.
These electrical quantities can be difficult to understand because they cannot be observed directly. To clarify these terms, we can make the comparison between electrical circuits and water flowing in pipes. Here is a chart of the three electrical units we will study in this experiment.
» Two resistors (about 56 and 82 ). Light bulb (6.3 V) «
Preliminary Questions (1-3)
Preliminary Setup (6)
Procedure (1-8, 10)
Analysis (1-8)
Note: Show all equations, calculations and very clear screenshots for the graphs with fits to receive full credit.
Data Tables
|
56 Ω Resistor |
82 Ω Resistor |
Light Bulb |
||||
|
Voltage (V) |
Current (A) |
Voltage (V) |
Current (A) |
Voltage (V) |
Current (A) |
Resistance (Ω) |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Slope of regression line (V/A) |
Intercept (V) |
Slope of proportional fit (V/A) |
Error in proportional fit (Ω) |
|
Resistor [ ± Ω] |
|
|
|
|
|
Resistor [ ± Ω] |
|
|
|
|
|
LED |
||
|
Voltage (V) |
Current (A) |
Resistance (Ω) |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Device |
Power (W) |
|
Light Bulb |
|
|
LED |
|
28
Lab. 5 Ohm s Law & Resistance The fundamental relationship among the three important electrical quantities current, voltage, and resistance was discovered by Georg Simon Ohm. The relationship and the unit of electrical resistance were both named for him to commemorate this contribution to physics. One statement f Oh a i ha he c e h gh a e i i i a he age ac he
resistor. In this experiment you will test the correctness of this law in several different circuits using a Current & Voltage Probe System and a computer.
These electrical quantities can be difficult to understand because they cannot be observed directly. To clarify these terms, we can make the comparison between electrical circuits and water flowing in pipes. Here is a chart of the three electrical units we will study in this experiment.
Electrical Quantity Description Unit
Water Analogy
Potential Difference or Voltage
Potential energy difference/unit charge of a charge at two points in a circuit.
Volt (V) 1 V = 1 J/C
Water pressure difference between two points in a pipe
Current Rate of flow of charge through a conductor.
Ampere (A) 1 A = 1 C/s
Rate of flow of water through a pipe
Resistance A measure of how difficult it is for charged particles to flow through a conductor.
Ohm ( ) A measure of how difficult it is for water to flow through a pipe.
OBJECTIVES Determine the mathematical relationship between current, potential difference, and resistance in a simple circuit.
Compare the potential difference vs. current behavior of a resistor to that of a light bulb and light emitting diode (LED).
MATERIALS computer two resistors (about 56 and 82 ) Labquest Mini connecting wires adjustable 6-volt DC power supply light bulb (6.3 V) current probe & voltage probe LED
PRELIMINARY QUESTIONS 1. A TV news reporter once stated that a person was electrocuted "when 20,000 volts of
electricity surged through his body." What is wrong with this description? What was it that "surged" through his body?
2. Do you expect the resistance of a light bulb to remain constant as the current through it is increased and the filament goes from red-hot to white-hot? Explain why or why not.