# Ch. 5 - Calculations

Science - Electricity
Calculations
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Slide 1: Slide
ScienceMiddelbare schoolvwoLeerjaar 2

This lesson contains 13 slides, with interactive quizzes and text slides.

Lesson duration is: 60 min

## Items in this lesson

Science - Electricity
Calculations

#### Slide 1 -Slide

You need to be able to:
• Making calculations with the formula of power:
• P = U x I

• Making calculations with the formula of resistance:
• R = U / I

• Making calculations with the formula of Electrical Energy:
• E = P x t

#### Slide 2 -Slide

Variable
Symbol
Unit
Symbol
Voltage
U
Volt
V
Current
I
Amps
A
Power
P
Watt
W
Resistance
R
Ohm
Energy consumption
E
kiloWatthour
kWh
Ω

#### Slide 3 -Slide

Julia measures a current of 0.8 A at a voltage of 12 V in a random circuit.
Calculate the resistance in this circuit.

P = U x I
R = U / I
E = P x t

#### Slide 4 -Open question

Explanation

Julia measures a current of
0.8 A at a voltage of 12 V in a random circuit. Calculate the resistance in this circuit.

• g:   U = 12 V I = 0.8 A
• a:   R = ?
• f:    R = U/I
• c:   R = 12 / 0.8 = 15 Ω
P = U x I
R = U / I
E = P x t

#### Slide 5 -Slide

Donna reads a voltage of 4.50 V and a resistance of
300 Ohms in a circuit.
Calculate the current (in mA) in this circuit.
P = U x I
R = U / I
E = P x t
P = U x I
R = U / I
E = P x t

#### Slide 6 -Open question

Explanation

4.50 V and a resistance of
300 Ohms in a circuit.
Calculate the current (in mA) in this circuit.

• g:   U = 4.5 V       R = 300 Ω
• a:   I = ?
• f:    R = U/I    -->  I = U / R
• c:   I = 4.5 / 300 = 0.015 A
• 0.015A = 15 mA
P = U x I
R = U / I
E = P x t

#### Slide 7 -Slide

A lamp is been lit all evening, about 5.5 hours. The lamp is plugged in the mains socket and the current through the lamp is 400 mA.

Calculate the energy consumption from this lamp and the costs of the use of this lamp if 1 kWh = 22 cents
P = U x I
R = U / I
E = P x t

#### Slide 8 -Open question

Explanation

A lamp is been lit all evening, about 5.5 hours. The lamp is plugged in the mains socket and the current through the lamp is 400 mA.

Calculate the energy consumption from this lamp and the costs of the use of this lamp if 1 kWh = 22 cents
• g:   U = 230 V        t = 5.5 h
•        I = 400 mA = 0.4 A
• a:   E = ?
• f:    E = P x t
•        But missing the P
•        So: first P = U x I

• c:  P = 230 x 0.4 = 92 W
•      E = 0.092 x 5.5 = 0.51 kWh
•      0.51 kWh x 22 = 11.13 cent
P = U x I
R = U / I
E = P x t

#### Slide 9 -Slide

the circuit has a total resistance of 30 Ohms. Calculate the power in this circuit.
P = U x I
R = U / I
E = P x t

#### Slide 10 -Open question

Explanation

John reads a voltage of 12V. In addition, the circuit has a total resistance of 30 Ohms. Calculate the power in this circuit.
• g:   U = 12 V       R = 30 Ω
• a:   P = ?
• f:    P = U x I
•        But missing the I
•        So: first I = U / R

• c:   I = 12 / 30 = 0.4 A
•        P = 12 x 0.4 = 4.8 W
P = U x I
R = U / I
E = P x t

#### Slide 11 -Slide

Camil has a lightbulb with a power of 50W. This bulb needs to be plugged into the mains socket, otherwise is won't work.
Calculate the resistance of this bulb
P = U x I
R = U / I
E = P x t

#### Slide 12 -Open question

Explanation

Camil has a lightbulb with a power of 50W. This bulb needs to be plugged into the mains socket, otherwise is won't work.
Calculate the resistance of this bulb
• g:   P = 50 W      U = 230 V
• a:   R = ?
• f:    R = U / I
•        But missing the I
•        So: first I = P / U

• c:   I = 50 / 230 = 0.22 A
•        R = 230 / 0.22 = 1045 Ω
P = U x I
R = U / I
E = P x t