Ohm\'s Law Practical PDF

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Prelim Physics - Ohm's Law Prac...

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Anson Tong 11PHYS_2 – Mr Barr

Ohm’s Law Practical Outcomes: Content: 





Investigate the quantitatively the current-voltage relationships in ohmic and non-ohmic resistors to explore the usefulness and limitations of Ohm’s Law using: W V= o q V o R= I Investigate quantitatively and analyse the rate of conversion of electrical energy in components of electric circuits, including the production of heat and light, by applying P=VI and E=Pt and variations that involve Ohm’s Law Investigate quantitatively the application of the law of conservation of energy to the heating effects of electric currents, including the application of P=VI and variations of this involving Ohm’s Law

Working Scientifically:   

Develops and evaluates questions and hypotheses for scientific investigation Analyses and evaluates primary and secondary data and information Explains and quantitatively analyses electric fields, circuitry and magnetism

Aim: How does the voltage and current change in a circuit with a resistor?

Risk Assessment: Risk Electric Shock

Rating Low

Hot electrical leads

Low

Tripping hazard

Low

Equipment:   

Electrical Leads x 6 Transformer x 1 Ammeters x 2

Minimisation Use only 8-10 volts on transformer Turn off transformer after use and wait for electrical leads to cool down Make sure that electrical lead on transformer is wrapped tightly after use

Anson Tong 11PHYS_2 – Mr Barr Voltmeter x 1 Resistor set x 1

 

Procedure: 1.) Setup the equipment in the diagram 2.) Plug the transformer into the wall socket 3.) Connect the negative DC terminal of the transformer to the negative terminal of the ammeter 4.) Connect the positive of the ammeter to the negative of the resistor set 5.) Connect the positive terminal of the resistor set to the negative ammeter 6.) Connect the positive terminal of ammeter back to the positive of transformer 7.) Go back to the resistor set and connect the voltmeter to the negative terminal of resistance set 8.) Connect positive terminal of resistor set to the voltmeter’s positive terminal 9.) Switch on the transformer to 2 volts and ensure that the resistor set is on 50 Ohms 10.) Record results one each transformer setting 11.) Change the resistance on the resistor set to 100 Ohms than 200 and repeat

Diagram:

Table of Results: Resistor

50 Ω 100 Ω

A1 V A2 A1

2 0.04 2.37 0.04 0.02

4 0.08 4.21 0.08 0.04

Transformer Settings 6 8 10 0.12 0.16 0.20 6.28 8.23 10.61 0.12 0.16 0.20 0.06 0.08 0.10

12 0.25 12.85 0.25 0.13

R=

V I

Avg = 53.7201 Ω Avg =

Anson Tong 11PHYS_2 – Mr Barr V A2 A1 V A2

200 Ω

2.39 0.02 0.01 2.44 0.01

4.24 0.04 0.02 4.33 0.02

6.31 0.06 0.03 6.43 0.03

8.44 0.08 0.04 8.50 0.04

10.75 0.10 0.05 10.85 0.05

13.09 0.12 0.06 13.15 0.06

106.940 1Ω Avg = 220.305 6Ω

Where A1 – First Ammeter, A2 – Second Ammeter and V – Voltmeter

Analysis: 1.)

Find the resistance of the resistor set 50 Ω, 100 Ω and V 200 Ω. Fill out the column and calculate the average I resistance in Ohms (Ω) in your results table. 2.) Draw a graph of V vs I . Find the gradient of the graph for the 50 Ω, 100 Ω and 200 Ω resistors. Compare the V gradient with the column in your results table. I Comment on:

V vs I 14 12

Voltage (V)

10 8 50 Ω

6 4 2 0

0

0.05

0.1

0.15

0.2

0.25

0.3

Current (I)

a.)

What does the gradient represent in a graph of V vs I . Find the gradient for each resistor. The gradient in the graph represents resistance as V/I is equal to R.  Gradient of the 50 Ω resistor is 49.9047 Ω  Gradient of the 100 Ω resistor is 85.6 Ω  Gradient of the 200 Ω resistor is 214.2 Ω Rise where rise first and last Run voltage value and run is first and last current value.

All gradients were found using

Anson Tong 11PHYS_2 – Mr Barr b.)

Are the gradients for 50 Ω, 100 Ω and 200 Ω similar to V the column result? Should they be different? Explain I why or why not? The gradients and the v/I column is similar but not the same. With the 50 Ω resistor being the closest and the 100 Ω resistor being furthest away from the value in the v/I column. The two values should be same as they are both the resistance of that circuit. However, the gradient was calculated using rise over run of the first and last points whereas the resistance in the table was calculated by averaging out the voltage and current. If all these points were linear then the gradient and table result would be the same. c.)Which of the graphs are Ohmic? Discuss All these graphs are Ohmic as the trend lines are linear. If these lines were curved or exponential then the ammeter would be non-ohmic. Ohmic just means that the object obeys Ohm’s law which is that the electric current is proportional to the voltage and inversely proportional to resistance. 3.) Why did we use two ammeters? What comment can you make about the reading on both ammeters? Explain In this experiment, two ammeters were used to observe the flow of electrons on either side of the circuit before and after going through a resistor. It can be concluded from this practical that the current does not change within the circuit as results on both ammeters remained the same.

Conclusion: 4.22 – Explanation of Ohm’s Law. Do your results confirm or refute Ohm’s Law? Ohm’s Law describes the relationships between voltage, current and resistance. It shows that the potential difference in electrical energy across an ideal conductor is proportional to the current. The constant of proportionality is resistance (R). Ohm’s Law is most commonly seen through the equation V =IR and the other variants derived from it. Where V = potential difference between the two points in the circuit, I = current flowing through the circuit and R for the resistance within the circuit. Any material that obeys this law that voltage is proportional to current is considered ohmic or linear. In this case, as the three lines within the graph are linear it can be concluded that the resistors were ohmic thus obeying Ohm’s Law.

4.2.3 & 4.2.5 – Discuss the conversion of electrical energy that involves Ohm’s Law for each resistor

Anson Tong 11PHYS_2 – Mr Barr As P=IV and V =IR we can substitute V into the power equation and get P=I 2 R . This shows that the total power output can be described as the current squared multiplied by the resistance within the circuit. This is especially useful for electrical engineers who are tasked with the job of laying out long electrical cables from one city to another. They can use this to calculate the power and work done as well as the loss of energy.

Extension Describe the current – voltage relationships in ohmic and nonohmic resistors to explore the usefulness and limitations of Ohm’s Law. V meaning that current is proportional to R voltage and inversely proportional to resistance. If rearranged this is seen through the graph where this relationships between these three variables are observed through a linear line. For non ohmic resistors this is not the case as resistance of the resistor changes. A common example of this is a lightbulb when increases in resistance as it beginnings to heat up. This means that although the current and voltage may stay the same the resistance will differ.

Ohm’s Law states that

I=

Figure 1. This graph shows the ohmic resistor as a linear function and the non-ohmic resistor as a curve or non-linear function. Overall, this shows that for non-ohmic resistors the resistance is not a constant and can change with voltage, current and even time. This means that these resistors do not obey Ohm’s Law.

Anson Tong 11PHYS_2 – Mr Barr

References: Name of Website https://physics.stackexchange.c Does V=IR om/questions/376415/does-v-ir- apply to a nonapply-to-a-non-ohmic-conductor ohmic resistor? https://www.fluke.com/enau/learn/bestWhat is Ohm’s practices/measurementLaw? basics/electricity/what-is-ohmslaw https://www.physicsforums.com Difference /threads/difference-betweenbetween ohmic ohmic-and-non-ohmicand non ohmic resistors.861778/ resistors Web Address

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Date Accessed

Physics Stack Exchange

15/08/19

Fluke

15/08/19

Physics Forum

15/08/19...