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## PowerPoint Slideshow about 'Unit Three: Ohm’s Law' - Jimmy

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Schedule

Unit Topic Chpt Labs

- Quantities, Units, Safety 1 2 (13)
- Voltage, Current, Resistance 2 3 + 16
- Ohm’s Law 3 5 (35)
- Energy and Power 3 6 (41)
- Series Circuits Exam I 4 7 (49)
- Parallel Circuits 5 9 (65)
- Series-Parallel Circuits 6 10 (75)
- Thevenin’s, Power Exam 2 6 19 (133)
- Superposition Theorem 6 11 (81)
- Magnetism & Magnetic Devices 7 Lab Final
- Course Review and Final Exam

Unit 3 Objectives - I

- Describe the relationship among voltage, current, and resistance.
- Given two of the three variables in Ohm’s Law, solve for the remaining quantity.
- Solve Ohm’s Law problems using metric prefixes.
- Construct basic DC circuits on a protoboard.

Unit 3 Objectives – II

- Use a digital multimeter (DMM) to measure a predetermined low voltage on a power supply.
- Measure resistances and voltages in a DC circuit using a DMM.
- Explain the Multisim workbench and show how to construct a basic circuit.
- Test circuits by connecting simulated instruments in Multisim

Reading Assignment

- Read and study
- Chapter 3: Ohm’s Law Pages 71-80

Lab Assignment

- Lab Experiment 5:
- Ohm’s Law Pages 35-38
- Complete all measurements, graphs, and questions and turn in your lab before leaving the room

Written Assignments

- Answer all questions on the homework handout
- Be prepared for a quiz on questions similar to those on the homework.
- If there are any calculations, you must show ALL your work for credit:
- Write down the formula
- Show numbers in the formula
- Circle answer with the proper units

Ohms Law

- MEMORIZE: V = I R
- Ohm’s Law
- If you increase the voltage, you increase the current proportionally
- 3 times the voltage gives you three times the current
- Resistance (ohms) is the proportionality constant and depends on the atomic structure of the material conducting the current

Ohm’s Law

- Memorize: V = I R
- Use algebra to find:
- I = V / R
- R = V / I
- If you can, learn all three variations, but you can get by if you memorize:

V = I R

Practice

- V = I R
- What voltage (V) is needed to push a current of 2 Amperes (I) through a resistance of 18 Ohms (R) ?

Practice

- V = I R
- What voltage (V) is needed to push a current of 2 Amperes (I) through a resistance of 18 Ohms (R) ?
- V = I R
- V = 2 A x 18 Ω
- V = 36 V

Practice

- V = I R
- What current (I) flows through a resistance of 8 ohms when the resistor is connect to a 24 volt battery?

Lab 5 - Ohm’s Law

- Ohm’s Law describes the relationship among voltage, current, and resistance – it does not control it!
- In lab, you will prove to yourself that Ohm’s Law applies to circuits
- Use the special handout to organize your information

Select and Measure Resistors

- Your resistors can off by +/- 5% from the marked value
- You must measure as accurately as possible the real resistance used in your experiment

Use TWO meters

- Use TWO DMMs in your experiment
- Record as many digits as possible for both voltage and current
- You must BREAK the circuit to measure current

A

V

Plot Your Points

- Your lab handout says to plot I along the x axis and V along the y axis
- The slope is Δy / Δx = ΔV/ ΔI
- Based on Ohm’s Law, R = V / I, just like the slope

Lab 4 – Voltage Measurement

1. Select the correct voltage mode (ac or dc).

2. Select range higher than expected voltage.

3. Connect the meter across the points. Red, positive (+), Black, common (–)

Next Steps

- 4. Reduce the range setting until the reading fails
- 5. Increase the range setting one step and record all the numbers, with the proper units, shown on the meter
- 34.67 mV, for example

Voltage Notation

- Voltage is always the difference between TWO points.
- Measure VBC by attaching the RED lead to B and the BLACK lead to C

A

B

V

D

C

Voltage

- If only one letter is given, attach the RED lead to that letter, and the BLACK lead to the reference point or ground.
- If D is your reference point, VB is:

A

B

D

C

V

Voltage Differences

- If D is your reference point, then
- VB is really VBD
- VC is really VCD
- Electrically, then
- VBC = VBD - VCD
- Voltage is the difference between two points
- Choosing a different reference point does NOT change the real voltage

Unit 3 Summary

1. Ohm’s Law

2. Solving for voltage, current, or resistance in a one-load circuit

3. Ohm’s Law using metric prefixes

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