Physics

Electromagnetism: Ohm's Law

Central Concept : Stationary and moving charged particles result in the phenomena known as electricity and magnetism

Lesson Plan

 

State Standards:

Learning Standard: Introductory Physics, High School

5.2 Develop qualitative and quantitative understandings of current, voltage, resistance, and the connections among them (Ohm's law).

Essential Question:

How do you know that the relationship between voltage, current and resistance is determined by Ohm's law?

Lesson Question:

What determines the amount of current that flows in an electric circuit?

Introduction:

The electric tools and appliances you use daily transfer electric energy to another form of energy. The electric circuit they belong to obeys Ohm's law. In this lesson you will be measuring the current in an electric circuit and the voltage (potential difference) across resistors (light bulbs) placed in series. After you discover the relationship between current, voltage and resistance you will be able to explain Ohm's law and solve problems involving electric circuits. Subsequent lessons will apply this investigation to resistors in parallel.

Task:

Your goal is to collect data on current, voltage and resistance in an electric circuit. You will create a graph of voltage verses current from the data and determine the slope line of best fit. An online excel spreadsheet will be used to compile the measurements of the whole class and will also aid in creating graphs. Data will also be obtained at home or in class using a PhET electric circuit simulation which will be added to existing measurements.

Lesson Experiences:

You will be grouped together in 2-3 students per group.
Begin your investigation by doing the Ohm's Law Activity 1.

Ohm's Law Activity 1

You will be creating a simple circuit using a battery connected to a light bulb and knife switch.

You will use an ammeter and voltmeter to measure the current in the circuit and potential difference (voltage drop) across the battery and light bulb. Readings will be recorded and analyzed.
The number of batteries and light bulbs will be varied and data recorded.

Procedure:


Sample Data Table

Leonard Martino Period 3 Date:

Voltage drop
across(V)

Current Flowing
before (A)

Current Flowing
after (A)

1 Battery

Light bulb #1

Light bulb #2

2 Batteries

Light bulb #1

Light bulb #2

Place your data in the spreadsheet. ( Activity 1 Worksheet link)


After you obtain your results, discuss these misconceptions:

  1. Voltage is measured as the potential difference across two points in a circuit.
  2. Charge moves through a circuit.

Web 2.0 : homework: PhET electric circuit simulation

Your Objective: Construct a series circuit and measure the voltage drop across each resistor and the current before and after each resistor in the circuit.

Instructions:

  1. Click on the DC circuit simulation below.
  2. Construct a series circuit using 1 battery and 2 light bulbs.
  3. Measure the voltage across the battery using the voltmeter and record the result.
  4. Measure the voltage across each light bulb using the voltmeter and record the result.
  5. Measure the current in the wire before and after each light bulb using the non-contact ammeter or the ammeter that you connect directly into the circuit and record the result.
  6. Join 2 batteries in series to the circuit and repeat steps 2-5 above.
  7. Place your collected data in the spreadsheet using the link below.
  8. Answer the two questions below by clicking on the link.

PhET Electric Circuit Simulation


Sample Data Table

Leonard Martino Period 3 Date:

Voltage drop
across(V)

Current Flowing
before (A)

Current Flowing
after (A)

1 Battery

Light bulb #1

Light bulb #2

2 Batteries

Light bulb #1

Light bulb #2

Place your data in the spreadsheet . (Activity 1 Worksheet link)

  1. State two things that you observed about the voltage across the battery and the voltage drop across each light bulb in the two circuits.
  2. State two things you know about the current flowing in a series circuit.

Click on the link to place your answers to the questions above.

Ohm's Law Activity 2


This activity may be started in class or outside of school.

Your Objective(s): Be able to:

Instructions:

Using the PhET electric circuit simulation, you will attach a battery, ammeter,light bulb and switch in series and connect a voltmeter across the light bulb.

Example diagram:

PhET Ohms Law Simulation

Sample Data Table

Leonard Martino Period 3 Date:

Voltage drop
across(V)

Current Flowing
before (A)

Current Flowing
after (A)

1 Battery

Light bulb #1

Light bulb #2

2 Batteries

Light bulb #1

Light bulb #2

You may place your data in the spreadsheet located online or on your own spreadsheet ( Activity 2 Worksheet link).

Continue the investigation at home by using the PhET electric circuit simulation and add that data to the spreadsheet.

Note: The slope of the line is the total resistance . Ohm's law V = RI or V/I = R where R is the resistance which is constant (constant slope)

Discuss your results with the group in the next class. What have you discovered? How does this relate to Ohm's Law?

Conclusion:

Now that you have completed this lesson you are able to create a simple circuit and connect an ammeter and voltmeter properly in order to measure current and voltage. By collecting data on current and voltage drops at various places in the circuit, you have
developed a qualitative and quantitative understanding of current, voltage, resistance, and their relationship to each other. Using a spreadsheet to organize your data and graphing that data allowed you to see the relationship between current,voltage and resistance and verify Ohm's Law.

Assessments:

You will be assessed on the completion of both investigations and producing a data table and graph which includes a line of best fit and calculated slope. A brief explanation (one paragraph) on the relationship between voltage, current and resistance is also required.

Other assessments will include:

When we have finished the section on series circuits you will take an online quiz to better enable you to assess your own understanding of electric circuits. You may take the quiz as often as you need to so that you will become confident in your knowledge of this section of the text. Click on the link below and choose any of the quizzes labeled "series circuit."

ZOHO online quiz series circuit quiz

To help you review the entire chapter using Quizlet flashcards click here.

Resources:

Assessment Rubric for Activity 1 and Activity 2

You will be able to....

Strong

Good

Adequate

Inadequate

Weighting

Arrange a simple circuit using a battery,
light bulb, switch, voltmeter and ammeter correctly

circuit is correct and meters
properly attached. Set up is
well organized and neat

circuit is correct but
contains minor
error

circuit correct
but contains a
few minor errors

circuit not properly set up

Create a simple circuit using computer simulation
program

circuit is correct and meters
properly attached. Set up is
well organized and neat

circuit is correct but
contains minor
error

circuit correct
but contains a
few minor errors

circuit not properly set up

Measure the voltage at various points in a circuit
as well as current

All voltage is measured
correctly
All current is measured
correctly

Minor error in
voltage and/or current measurements

Few minor errors in
voltage and/or current measurements

Major errors in
voltage and/or
current measurements

Organize data collected using Excel spreadsheet

data is well organized and easily
read

data is organized but
contains minor errors

data organized but
contains some errors
or is not easily read

Excel not used

Create a Mass verses Volume graph of data using
Excel or graph paper

Graph is correct and
with title, axises labeled and line of best fit shown.
Slope of line is calculated.

Graph is correct with
few errors

Graph is correct but
contains a major error

graph is not correct
or is missing

Describe quantitatively the relationship between
voltage, current and resistance.

Description is excellent

Description is good
but may contain some
error

Description is adequate but is clearly stated

Description is not
clear or is incorrect

Explain Ohm's law and solve problems involving
current, potential difference
and resistance.

Explanation and all problems are correct

Explanation is correct
but problems have minor errors

Explanation and/or
problems have few errors

Explanations and/or
problems have major errors

 

Resources:

Eisenkraft, Arthur. Active physics A Project-Based Inquiry Approach . 3rd ed. New York: Herff Jones Company, 2010.
Zitzewitz, Paul. Physics Principles and Problems .Ohio: Glenco/McGraw Hill Companies.2009.

Resources:
http://phet.colorado.edu/
http://www.zoho.com/creator/
http://quizlet.com/math-and-science/
http://www.youtube.com/watch?v=tUCtCYty-ns&feature=youtube

anmeter, voltmeter or multimeter, 2 D -size batteries with holders, 2 miniature light bulbs with holders, connecting wires, knife switch

ZOHO online quiz

Quizlet flashcards

Worksheets:

Series circuit data worksheet

voltage/current activity1 worksheet

series/circuit data activity2 worksheet

Worksheets also available on Google Docs.

 

Image credits:

"Circuit" by Mamun2a, from Wikimedia Commons

"Multimeter" by Neo139, from Wikimedia Commons

"Bombeta de llum" from Wikimedia Commons.