Ohm’s Law Coursework Example

Lab Report: Ohm’s Law
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Institution Affiliation

Introduction
Ohm’s law is a fundamental principle in electrical engineering as it relates the voltage applied to the ends of a resistor and the current that flows through the resistor. The law dictates that the electric potential difference across an ideal conductor relates directly to the current that flows through the conductor that is V∝A whereby V is the electric potential, and A is the current. Thus, the equation can be expressed as V=RA whereby R is a proportionality constant known as resistance. On the other hand, the power lost through the conductors is given by P(Watts)=I2R=V2R.
Materials that obey Ohm’s law are known as Ohmic materials while electric components made from the ohmic materials are known as resistors. In an experiment to determine ohm’s law, voltmeters and ammeters are used to measure voltage drop and current respectively while the resistors serve as the ideal conductor.
Objectives
To verify ohms
To determine the power dissipated by resistors
To connect and use variable resistors when verifying ohm’s law
To familiarize with different circuit connections as well as connect, use, and read ammeters.
To determine the behavior of the electrical voltage and corresponding current for a simple resistor and a standard tungsten-filament light bulb
Materials
1 each power supply
2 each digital multi-meter (DMM)
1 each small circuit experiment board
6 each electrical lead cables
1 each rheostat
Hypothesis
The potential difference across a resistor relates directly to the current that flows through it.

Exercise 1: Measuring the Current and Voltage for a Nominal 100 Ω Resistor
In this exercise, the current and the voltage through a known resistor were measured. The current through the circuit was varied using a rheostat while the voltage remained constant.
Procedure
The power supply was set at 5.0 V.
The rheostat’s maximum resistance was set by moving the slide such that the currentpassed through the entire coil.
The switch was closed by reconnecting the electrical lead to the power supply.
The rheostat was adjusted at intervals of 0.5 V and the corresponding ammeter andvoltmeter readings recorded. The procedure was repeated once to verify the readings.
Exercise 1 results
Voltage(V) Current(mA)
0.5 5
1 10
1.5 15
2 20
3 31.4
3.5 36.6
4 42.3
4.5 47.7
5 52.9

b)
V mA
0.5 0.53
1 10.6
1.5 15.9
2 21.4
2.5 26.6
3 31.9
3.5 37.4
4 42.4
4.5 47.8
5 53.1
Current through the 100 Ω resistor when resistance is maximum is given by I=VR=5V100 Ω =0.05 A
Maximum power dissipated by the 100 Ω is given by P=V×I=5V×0.05=0.25 WExercise 2: Measuring the Current and Voltage of a Light Bulb
Procedure
A similar circuit to that in exercise 1 was built, and the 100 Ω resistor was replaced with a small light bulb.
The largest current scale on the ammeter was connected to the circuit, and the power supply was set at 5 volts.
The voltage across the light bulb was then varied at intervals of 0.1 volts from 0.1 to 0.5 volts. The interval was then changed to 0.5 volts from 0.5 to 5 volts. The current through the bulb as well as the behavior of the bulb was recorded for each voltage. The behavior of the bulb was recorded as off, dim red, dim white, white, bright, and very bright.

Analysis

Exercise 2 results
V mA Brightness
0.1 22.1 The light bulb is off
0.2 35.2 0.3 41.3 0.4 45.9 0.5 51.3 1 71.8 Start having light
1.5 88.2 Growing lighter and lighter.
2 102.8 2.5 105.1 3 120 3.5 130 4 149 4.5 160 4.61 168.8
Analysis

Discussion
In exercise 1, the data points are closely scattered, and they produce the best fit line that supports ohms law, and hence the resistor exhibits ohmic behavior. A graph of the deviation points shows that the points deviate from the best fit line consistently. According to Allain (2011), the consistent deviation can be compared to the experimental errors. In the experiment, the errors are not significant and may have been caused by the apparatus used in the experiment. The gradient of the graph which equals to the change in voltage divided by the change in current equals the resistance of the material. In our experiment, the gradient of the line is equivalent to the square root of 0.9932 which approximates to 1. The equation of the line is given by y = 0.5833x – 0.1389.
In the second experiment, the graph portrays a complicated behavior as the scatter points produce a curve rather than a straight line. At low voltage, the graph produced by the bulb was curved but becomes linear as the voltage is increased. Thus the gradient of the best fit line cannot be compared to the resistance of the bulb.
Conclusion
The experiment supports the hypothesis which states that the potential difference across a resistor relates directly to the current that flows through it. Materials exhibit such properties are known as ohmic materials, and they include resistors. However, the unusual characteristics from the bulb arise as the bulb becomes hotter as it gets brighter implying that an increase in temperature increases the resistance of a conductor.

Reference
Allain Rhett (July 4, 2011). “How to find the uncertainty in the slope.” Introductory Physics Lab. Retrieved (March 7, 2018) https://www2.southeastern.edu/Academics/Faculty/rallain/plab193/page1/page35/page36/page36.html