ohm’s law foundations of technology ohm’s law © 2013 international technology and engineering...

Foundations of Technology

Ohm’s LawOhm’s Law

© 2013 International Technology and Engineering Educators Association, STEMCenter for Teaching and Learning™ Foundations of Technology

Teacher Resource – Unit 4 Lesson 4

The BIG IdeaThe BIG Idea

Big Idea:

Troubleshooting allows users to continue to use and maintain the proper operation of a system or product.


Proposed by George Ohm, and is the relationship between Voltage, Current and Resistance.

Voltage (V) = Current (I) X Resistance (R)



-

+V

R

I

V

I R

Ohm’s Law is commonly expressed using the triangle found below where:

Voltage (V) = Current (I) X Resistance (R)

Current (I) = _Voltage (V)__ Resistance (R)

Resistance (R) = _Voltage (V)_ Current (I)



V

I R

Voltage (V) is the electrical force that moves electrons through a conductor.

Voltage is electrical pressure that pushes electrons.

VoltageVoltage


V

I R

Current (I) is the quantity or flow rate of electrons moving past a point.

Current flow is also known as amperage, or amps for short.

CurrentCurrent


V

I R

Resistance (R) is the force that reduces or stops the flow of electrons and opposes voltage.

ResistanceResistance


V

I R

Using Ohm’s Law determine the missing value for the following circuit:

Practice QuestionsPractice Questions


V

I R

-

+V

R

I

4.5

0.5 Amp

= ______Ώ

Using Ohm’s Law determine the missing value for the following circuit:



V

I R

-

+V

R

I

4.5

0.5 Amp

= ______Ώ

Resistance (R) = Voltage (V) Current (I)

R = 4.5V 0.5Amp

R = 9Ώ



V

I R

-

+V

R

I

10 Ώ

0.5 Amp

_____

I = ______ Amp



V

I R

-

+V

R

I

10 Ώ

0.5 Amp

_____

I = ______ Amp I = 0.5 Amp - Current will be the same throughout the circuit

Voltage (V) = Current (I) x Resistance (R)

V = 0.5 Amp x 10 Ώ

V = 5V

In a Series circuit, the current through two or more resistors is the same, and the circuit is connected in a series.

The total resistance of the collection is the sum of individual resistances.

Resistors in SeriesResistors in Series


The total resistance of the collection is the sum of the individual resistances.

The Equivalent Resistance of R1, R2 and R3 when connected in series is:

R = R1 + R2 + R3

Resistors in SeriesResistors in Series


Calculate the total resistance of the series circuit:



V

I R

-

+V

I

9

5 Ώ

10 Ώ

3 Ώ

Calculate the total resistance of the series circuit:



V

I R

-

+V

I

9

5 Ώ

10 Ώ

3 Ώ

R = R1 + R2 + R3

R = 3 Ώ + 10 Ώ + 5 Ώ

R = 18 Ώ

Calculate the total current of the series circuit: (current is the same throughout a series circuit)



V

I R

-

+V

I

9

5 Ώ

10 Ώ

3 Ώ

R(total) = 18 Ώ

Calculate the total current of the series circuit:(current is the same throughout a series circuit)



V

I R

-

+V

I

9

5 Ώ

10 Ώ

3 Ώ

R(total) = 18 Ώ

Current (I) = Voltage (V) Resistance (R)

I = 9V 18 Ώ

I = 0.5 Amp

Using Ohm’s Law, calculate the voltage drop for each resistor in the series circuit:



V

I R

-

+V

I

9

5 Ώ

10 Ώ

3 Ώ

0.5 Amp




V

I R

-

+V

I

9

5 Ώ

10 Ώ

3 Ώ

V = I x R

V(R1) = 0.5 Amp x 3 ΏV(R1) = 1.5 V

V(R2) = 0.5 Amp x 10 ΏV(R2) = 5 V

V(R3) = 0.5 Amp x 5 ΏV(R3) = 2.5 V

0.5 Amp




V

I R

-

+V

I

9

5 Ώ

10 Ώ

3 Ώ

R1 R2 R3 Total

1.5 5 2.5 9 V Voltage

0.5 0.5 0.5 0.5 Amp Current

3 10 5 18 Ώ Resistance

Remember Current (I) is the same across a

series circuit.

0.5 Amp

In a Parallel circuit, the voltage through two or more resistors is the same, and the circuit is connected in parallel.

The total resistance of the collection is divided among the three resistors .

Resistors in ParallelResistors in Parallel


The total resistance of the collection is divided among the three resistors.

The Equivalent Resistance of R1, R2 and R3 when connected in parallel is:

1/R = 1/R1 + 1/R2 + 1/R3

Resistors in ParallelResistors in Parallel


Calculate the total resistance of the parallel circuit:



V

I R

-

+V

14.4 Amp

10 Ώ 1 Ώ

2 ΏI

Calculate the total resistance of the parallel circuit:



V

I R

1/R = 1/R1 + 1/R2 + 1/R3

1/R = 1/(10 Ώ) + 1/(2 Ώ) + 1/(1 Ώ)

1/R = 0.1 Ώ + 0.5 Ώ + 1 Ώ

1/R = 1.6 Ώ

R = 1/(1.6 Ώ)

R = 0.625 Ώ

-

+V

14.4 Amp

10 Ώ 1 Ώ

2 ΏI

Calculate the total voltage of the parallel circuit: (voltage is the same across a parallel circuit)



V

I R

R(total) = 0.625 Ώ

-

+V

14.4 Amp

10 Ώ 1 Ώ

2 ΏI

Calculate the total voltage of the parallel circuit:



V

I R

R(total) = 0.625 Ώ

Voltage (V) = Current (I) x Resistance (R)

V = 14.4 Amp x 0.625 Ώ

V = 9V

-

+V

14.4 Amp

10 Ώ 1 Ώ

2 Ώ

Calculate the total voltage of the parallel circuit: (voltage is the same across a parallel circuit)

I

Using Ohm’s Law, calculate the current across each resistor in the parallel circuit:



V

I R

-+

V

I

9

10 Ώ 1 Ώ

2 Ώ

14.4 Amp




V

I R

-+

V

I

9

10 Ώ 1 Ώ

2 Ώ


I(R1) = 9V 10 Ώ

I(R1) = 0.9 Amp14.4 Amp




V

I R

-+

V

I

9

10 Ώ 1 Ώ

2 Ώ


I(R2) = 9V 2 Ώ

I(R2) = 4.5 Amp14.4 Amp




V

I R

-V


I(R3) = 9V 1 Ώ

I(R3) = 9 Amp2 Ώ

+

I

9

10 Ώ 1 Ώ

14.4 Amp




V

I R

R1 R2 R3 Total

9 9 9 9 V Voltage

0.9 4.5 9 14.4 Amp Current

10 2 1 0.625 Ώ Resistance

Remember Voltage (V) is the same across a

parallel circuit.2 Ώ

+

I

9

10 Ώ 1 Ώ

14.4 Amp

V

ohm’s law foundations of technology ohm’s law © 2013 international technology and engineering...

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