unit three ohm s law
Download
Skip this Video
Download Presentation
Unit Three: Ohm’s Law

Loading in 2 Seconds...

play fullscreen
1 / 44

Unit Three: Ohm’s Law - PowerPoint PPT Presentation


  • 324 Views
  • Uploaded on

ET115 DC Electronics. Unit Three: Ohm’s Law. John Elberfeld [email protected] WWW.J-Elberfeld.com. 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)

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

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


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
schedule
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
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
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
Reading Assignment
  • Read and study
  • Chapter 3: Ohm’s Law Pages 71-80
lab assignment
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
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
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
graph of data
Graph of Data

V

Voltage

x

x

x

x

x

I – Current in Amps

reasoning
V = I RReasoning
  • Ohms Law: V = I R
  • High voltage produces high current for a given resistance
  • Low voltage produces low current for a given resistance
  • For a given voltage, a high resistance produces a low current
  • For a given voltage, a low resistance produces a high current
electronic circuit
Electronic Circuit
  • A battery with the voltage V pushes a current I through a resistor R

V = I R

ohm s law
V = I ROhm’s Law
  • This is the BIG IDEA for the day (year)!
  • V = I R
  • What if we divide both sides by R?
  • V = I R R R
  • But R/R = 1, so we don’t need to write it down:
  • I = V I = V / R R
ohm s law14
V = I ROhm’s Law
  • V = I R
  • What if we divide both sides by I?
  • V = I R I I
  • But I / I = 1, so we don’t need to write it down:
  • R = V R = V / I I
ohm s law15
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
Practice
  • V = I R
  • What voltage (V) is needed to push a current of 2 Amperes (I) through a resistance of 18 Ohms (R) ?
practice17
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
examples
? V

1.2k Ω

575 μA

Examples
  • Ohms Law: V = I R k = 103μ = 10-6
  • How much voltage must be connected across a 1.2 k Ω resistor to cause 575 μA of current to flow?
  • V = I R
examples19
19Examples

Ohms Law: V = I R k = 103μ = 10-6

How much voltage must be connected across a 1.2 k Ω resistor to cause 575 μA of current to flow?

V = I R

V = 575 μA 1.2 k Ω

V = .69V = 690 x 10-3V = 690 mV

? V

1.2k Ω

575 μA

examples20
10 V

25 Ω

103=k10-3 = m10-6 = μ

Examples
  • Ohms Law: V = I R
  • How much current flow through a 25 Ω resistor with 10 V across it?
  • V = I R I = V / R
examples21
21Examples

Ohms Law: V = I R

How much current flow through a 25 Ω resistor with 10 V across it?

V = I R I = V / R

10 V = I 25 Ω

I = 10 V / 25 Ω

I = .4 A or 400 x 10-3A = 400 mA

10 V

25 Ω

103=k10-3 = m10-6 = μ

examples22
35 V

250 mA

103=k10-3 = m10-6 = μ

Examples
  • Ohms Law: V = I R
  • If a certain resistor allows 250 mA to flow when 35 V are across it, what is the resistance?
  • V = I R R = V / I
examples23
35 V

250 mA

103=k10-3 = m10-6 = μ

Examples
  • Ohms Law: V = I R
  • If a certain resistor allows 250 mA to flow when 35 V are across it, what is the resistance?
  • V = I R R = V / I
  • 35 V = 250 mA R
  • R = 35 V / 250 ma
  • R = 140 Ω
examples24
4.5 mV

3.3k Ω

103=k10-3 = m10-6 = μ

Examples
  • Ohms Law: V = I R
  • How much current flow through a 3.3k Ω resistor with 4.5 mV across it?
  • V = I R I = V / R
examples25
4.5 mV

3.3k Ω

103=k10-3 = m10-6 = μ

Examples
  • Ohms Law: V = I R
  • How much current flow through a 3.3k Ω resistor with 4.5 mV across it?
  • V = I R I = V / R
  • 4.5 mV = I 3.3k Ω
  • I = 4.5 mV / 3.3k Ω
  • I = 1.36 μ A
practice29
Practice
  • V = I R
  • What current (I) flows through a resistance of 8 ohms when the resistor is connect to a 24 volt battery?
practice30
V = I RPractice
  • What current (I) flows through a resistance of 8 ohms when the resistor is connect to a 24 volt battery?
  • V = I R I = V / R
  • 24 V = I x 8 Ω I = 24 V / 8 Ω
  • I = 24 V / 8 Ω I = 3 A
  • I = 3 A
practice32
V = I RPractice
  • What size resistor allows 2 amperes of current through it when it is connected to a 10 Volt power supply?
practice33
V = I RPractice
  • What size resistor allows 2 amperes of current through it when it is connected to a 10 Volt power supply?
  • V = I R R = V / I
  • 10 V = 2 A x R R = 10 V / 2 A
  • R = 10 V / 2 A R = 5 Ω
  • R = 5 Ω
lab 5 ohm s law
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
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 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
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
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
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 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
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
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
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

ad