4.4 Power and energy

4.4 Power and energy
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Slide 1: Slide
physicsMiddelbare schoolhavo, vwoLeerjaar 2

This lesson contains 15 slides, with interactive quizzes, text slides and 1 video.

time-iconLesson duration is: 45 min

Items in this lesson

4.4 Power and energy

Slide 1 - Slide

ELECTRICAL POWER
The power indicates how much elektrical energy a device uses per second.

Slide 2 - Slide

Which device uses most power?
A
Mobile phone
B
Calculator
C
Hair dryer
D
Dish washer

Slide 3 - Quiz

When is your Phone using most energy?
A
reading in night modus
B
reading in regular modus
C
watching You Tube
D
sending an app

Slide 4 - Quiz

Power depends on:

VOLTAGE:
Voltage tells you how much energy a single particle supplies to the device
CURRENT:
Current tells you how many particles are delivering their energy every second

Slide 5 - Slide

In formula:
P = U x I 
U = voltage in Volts (V)
I = current in Amps (A)
P = power in Watts (W)

Slide 6 - Slide

Example
A toy train works on 12 Volts and 1,5 Amps. Calculate the power.

Slide 7 - Slide

Solution
Given: U = 12 V
               I = 1,5 A
Asked: P
Solution: P = U x I
               P = 12 V x 1,5 A 
               P = 18 W

Slide 8 - Slide

Example
A hairdryer is working on a current of 6 A.
Calculate the power of the hairdrayer.

Slide 9 - Slide

Solution
Given: I = 6 A
The hairdryer is plugged into the socket, so U = 230 V
Asked: P
Solution: P = U x I
P = 230 x 6 
P = 1380 W

Slide 10 - Slide

The power of a lamp is 75 Watts. The voltage is 230 Volts. What is the current (2 decimals) through the lamp?

Slide 11 - Open question

Example
A LED flash light has an power of 4 Watts. The current through the LEDs is 900 mA. Calculate the voltage of the batteries.

Slide 12 - Slide

Solution
Given: P = 4 W
I = 900 mA = 0.9 A
Asked: U
Solution: P = U x I
U = P : I
U = 4 : 0.9 
U = 4,4 V

Slide 13 - Slide

Power, time and energy consumption
The greater the power of a device, the more quickly the battery will run out . 
Therefore it is important to keep the power consumption of a device low: lower the volume, use energy saving lights (e.g. LEDs). 
This is an interesting factor for designers :-)

Slide 14 - Slide

Slide 15 - Video