Math for the trades 4

Math for the trades 4

Equations and formulas

Equations and formulas

In order to use Ohm’s law to check the voltage of a motor or determine where to place holes for an exhaust pipe, you’ll learn how to solve problems using equations with one unknown quantity.

OHM'S LAW

If you decide to become an electrician, you will definitely need to master Ohm's Law—an equation used to study electrical circuits, and figure out voltage, current, and resistance.

The basic equation is E = I X R. That translates to Voltage = Current x Resistance. 

Electricians use Ohm's Law to determine the current of a circuit, voltage drop, power loss, and conductor resistance.

120V supplies a lamp that has a resistance of 192 ohms.

What’s the current flow in the circuit?

In this example, you know voltage and you know resistance, but you don't know current.

You apply Ohm's Law like this:

I = E/R (Current = 120V/192 ohms).

Your answer is I = 0.625A.

The triangle helps you figure out what operations to use.

Multiple Choice

If the battery produced 12.6 Volts and what would be the current flow be for a 6 Ohm resistor

• 2.1 Amps

• 2.4 Amps

• 1.71 Amps

• 15 Amps

Multiple Choice

What resistance is needed to cause a 20A current flow because of a 100V battery?

• 0.2Ώ

• 2000Ώ

• 120Ώ

• 5Ώ

Multiple Choice

What resistance is needed to cause a 50A current flow because of a 500V battery?

• 10Ώ

• 5Ώ

• 2500Ώ

• 550Ώ

Multiple Choice

What voltage is needed to cause a 2A current flow through a 10Ω resistor?

• 5V

• 0.2V

• 20V

• 200V

Multiple Choice

How do you calculate voltage?

• Current X Resistance

• Resistance ÷ Current

• Current ÷ Resistance

• Measure it with a ruler

Multiple Choice

If the Voltage stays the same and Resistance is increased, Current will

• Increase

• Decrease

• Stay the same

• X

Multiple Choice

If the Voltage is increased and the resistance stays the same, Current will

• Increase

• Decrease

• Stay the same

• X

Multiple Choice

Voltage divided by Current

(V / I)

• Current

• Power

• Resistance

• Watts

Multiple Choice

Voltage divided by Resistance

(V / R)

• Current

• Power

• Ohms

• Watts

Multiple Choice

Current times Resistance equals

(I X R)

• Power

• Voltage

• Amperage

• Ohm

Multiple Choice

What is the Voltage of a circuit that has a resistance of 5 Ω and a current of 2 A?

• 25 V

• 10 V

• 2.5 V

• 0.4 V

Multiple Choice

What is resistance measured in?

• Ω (Ohms)

• V (Volts)

• A (Amps)

• W (Watts)

Multiple Choice

What is current measured in?

• Ω (Ohms)

• V (Volts)

• A (Amps)

• W (Watts)

Multiple Choice

What size resistor would produce a 3 Amp current flow with a 12 Volt battery

• 1 Ohm

• 3 Ohms

• 4 Ohms

• 12 Ohms

Multiple Choice

10/100 of 1000

• 100

• 10

• 1000

• 10000

Multiple Choice

1/3 of 9

• 9

• 1

• 19

• 3

Multiple Choice

4/5 of 60

• 12

• 24

• 48

• 58

Multiple Choice

7/9 of 27

• 21

• 27

• 20

• 22

Multiple Choice

3/11 of 55

• 5

• 10

• 55

• 15

Multiple Choice

1/7 of 49

• 7

• 14

• 21

• 28

Multiple Choice

1/6 of 54

• 18

• 9

• 27

• 36

Multiple Choice

3/4 of 100

• 25

• 50

• 100

• 75

Multiple Choice

3/7 of 63

• 9

• 27

• 18

• 24

Multiple Choice

1/3 of 30

• 20

• 30

• 40

• 10

Multiple Choice

8/9 of 72

• 8

• 64

• 24

• 40

Multiple Choice

1/3 of 30

• 20

• 30

• 40

• 10

Multiple Choice

1/12 of 144

• 12

• 144

• 1

• 24

Multiple Choice

3/8 of 48

• 6

• 12

• 18

• 30

Multiple Choice

2/3 of 24

• 8

• 16

• 24

• 42

Multiple Choice

4/8 of 50

• 25

• 100

• 50

• 2

Multiple Choice

1/9 of 81

• 27

• 72

• 9

• 108

Multiple Choice

3/8 of 56

• 21

• 7

• 41

• 156

Multiple Choice

1/8 of 64

• 12

• 15

• 16

• 8

Multiple Choice

3/5 of 25

• 5

• 10

• 15

• 30

Multiple Choice

1/5 of 60

• 12

• 3

• 89

• 24

Multiple Choice

What part of the circle is green?

• 2 out of 
• 2/3
• 1/3

Multiple Choice

What part of the circle is green?

• 1/3
• 2/3
• 3/1

Multiple Choice

What part of the circle is green?

• 1/2
• 2/1
• 1/4

Multiple Choice

What part of the circle is green?

• 1/3
• 3/1
• 1/4

Multiple Choice

Moby sliced an apple into 2 equal parts. He ate 1 slice. What fraction of the apple did he eat?

• 1/2
• 1/3
• 1/4

Multiple Choice

What is another way to write one-third?

• 1/2
• 1/3
• 3/1

Multiple Choice

If a pizza is divided into quarters, how many equal slices are there?

• 2
• 4
• 3

Multiple Choice

What fraction shows one out of four equal parts?

• 4/1
• 4/4
• 1/4

Multiple Choice

 $15\ \times\ \frac{2}{5}$  Answer in simplest form

• 6

• 30

•  $\frac{30}{5}$  

•  $\frac{1}{2}$  

Multiple Choice

 $16\ \times\ \frac{3}{8}\ \$   Answer in simplest form

•  $\frac{48}{8}$  
  

•  $\frac{16}{8}$  

• 3

• 6

Multiple Choice

Solve:

 $17=\frac{c}{-5}$  

• 85 = c

• -85 = c

• 3.4 = c

• -3.4 = c

Multiple Choice

Solve:

 $\frac{a}{-9}=12$  

• a = -1.3

• a = 1.3

• a = 108

• a = -108

Multiple Choice

How do you solve?

 $3x\equiv12$  

•  $+3\ on\ both\ sides$  

•  $-3\ on\ both\ sides$  

•  $\div3\ on\ both\ sides$  

Multiple Choice

How do you solve?

 $x-3=4$  

•  $-3\ on\ both\ sides$  

•  $+3\ on\ both\ sides$  

•  $\times3\ on\ both\ sides$  

•  $\div3\ on\ both\ sides$  

Multiple Choice

How do you solve?

 $x+5=10$  

•  $-5\ on\ both\ sides$  

•  $+5\ on\ both\ sides$  

•  $\div5\ on\ both\ sides$  

•  $\times5\ on\ both\ sides$  

Multiple Choice

Solve the equation:
20.5 = x + 4

• 16.5
• 16.05
• 24.5
• 24.05

Multiple Choice

 $\frac{x}{5}=20$  

• 100

• 120

• 4

• 5

Multiple Choice

Solve the equation:

2p = 16

• p = 32

• p = 12

• p = 18

• p = 8

Multiple Choice

S + 4 = 24

• S = 28

• S = 6

• S = 18

• S = 20

Multiple Choice

r + 20 = 27

• r = 7
• r = 47
• r = 13
• r = 20

Multiple Choice

Solve for x:

• x = 20
• x = 7
• x = 10
• x = 3

Multiple Choice

Solve:

 $\frac{3}{5}h\ =27$  

• h = 27

• h = 135

• h = 45

• h = 16.2

Multiple Choice

Solve the equation:

4p = 16

• p = 12

• p = -12

• p = -4

• p = 4

Multiple Choice

Solve the equation:

4p = 16

• p = 12

• p = -12

• p = -4

• p = 4

Poll

This material was helpful.

• Yes and I understood it.

• Yes and I would like more practice.

• No, I knew all of this material and got 100% on all of the questions without using a calculator.