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Circuit Breakers and Electrical Items Explore. Lesson 1

2.

Starter activity
What are the two types of current? Briefly describe each.
Alternating current
Direct current
A.C. both
directions
D.C. one direction

5.

Circuit Breakers and Electrical Items
Explore Lesson 1

Learning Objectives
Understand the uses of insulation, double insulation, earthing, fuses
and circuit breakers in a range of domestic appliances
Understand why a current in a resistor results in the electrical
transfer of energy and an increase in temperature, and how this can
be used in a variety of domestic contexts
Know and use the relationship between power, current and voltage:
- Power = current x voltage (P=IxV) - and apply the relationship to
a selection of appropriate fuses

7.

Learning Objectives
Use the relationship between energy transferred, current, voltage,
and time:
- Energy transferred = current x voltage x time (E=IxVxt)
Understand the difference between mains electricity being
alternating current (AC) and direct current (DC) being supplied by a
cell or battery

8.

Circuit Builder
Head to the learning platform. Your first task can be
found in week 10 and is called:
Week 10 PHY Explore Activity – Interactive Lab
Follow the instructions step by step, and be prepared
to show your findings and circuits on screenshare!

9.

Golden link
Can you remember the names of the different units used in electricity?
Make a list and share in the poll.
Pick one and describe what it represents. Hint: Often one unit encompasses two
other units!
Now…Write down and share on the chat pod how you think we make circuits safe.

10.

What is Power?
POWER = CURRENT X VOLTAGE
Electrical power is the rate at which
energy is transferred by a circuit.
It is measured in either Watts (W) or
Joules per second (J/s).

11.

Some typical power ratings
1000W
8000W
700W
600W
1400W
1100W
100W
4000W
4W
600W
1500W

12.

How can we tell if an appliance is energy
efficient?
In the UK, domestic
appliances are
required to carry
information on their
energy use to give
buyers an idea of
their running costs
and encourage us
to be greener and
use less energy.

13.

Electrical Power
60W
The bulb converts 60J of electrical energy
into 60J of heat and light energy
every second.
60W = 60J/s
The bulb converts 100J of electrical energy
into 100J of heat and light energy
every second.
The 100W bulb has a higher power rating.
100W

14.

Electrical Power
Power is measured in joules per second or watts (W).
The power (P) of an appliance is related to the voltage (V) across it
and the current (I) flowing through it.
• P (power) = I (current) x V (voltage)
• P (W) = I (A) x V (V)

15.

Calculating Electrical Power
Examples
1. What is the power of a 230V, 300A television?
Power = 300 x 230 = 69,000W
2. What is the power of a 230V, 6A bulb?
Power = 6 x 230 = 1380W

16.

Calculating Electrical Power
Calculate the correct fuse that should be used for a 230V,
2kW hair dryer. The most common fuses: 3A, 5A and 13A.
This is a common “rearrange” question you might come
across at GCSE. Let’s look at how it can be calculated…

17.

Calculating Electrical Power
Calculate the correct fuse that should be used for a 230V, 2kW
hair dryer. The most common fuses: 3A, 5A and 13A.
• P=IxV
• I=P/V=2000/230 = 8.7A
• The correct fuse for this hair dryer is 13A.
• The correct fuse for a circuit is the one that allows the correct
current to flow but that blows if the current is a little larger.
• If the correct current is 2A then it should be protected with a 3A
fuse.

18.

Calculating Electrical Power
Examples
What is the current when the potential difference is 70V and the
power supply is 35W?

19.

Calculating Electrical Power
Examples
What is the potential difference when the current is 20A and the
power supply is 60W?

20.

Calculating Electrical Power
Examples
What is the potential difference when the current is 300mA and the
power supply is 90W?

21.

Plenary: Explore Activity
Now complete the task on the learning platform:
Week 10 PHY Explore Activity – Which fuse to use?

22.

23.

24.

Lesson complete!
See you next lesson

25.

This lesson is
being recorded

26.

27.

Year 10 Physics
Week 10

28.

Circuit Breakers and Electrical Items
Explore Lesson 2

29.

Starter activity
Which device is the most powerful? Answer on the poll.
• Device A which has a current of 60A at a potential difference of
30V.
• Device B which has a current of 80A at a potential difference of
30V.
• Device C which has a current of 60,000 mA at a potential
difference of 30V.
Device B
Because it has
the highest
current
With the same
potential
difference
Therefore it must
be transferring
more energy

30.

31.

32.

Let’s start by reviewing our knowledge of the
equation P = IV
Try the task – Week 10 PHY Explore Activity – Power
Calculations
Now, let’s move on a step, and use the values to calculate
the energy transferred by an appliance…

33.

Calculating the total energy transferred by an
appliance
The power of an appliance tells you how much energy it
transfers each second. This means the total energy transferred
by an appliance is equal to its power multiplied by the length of
time the appliance is being used.
Energy (joules) = power (watts) × time (seconds)
E=P×t
E=I×V×t

34.

E = Pt
Table and animation showing energy usage
0J
Contex Energy
t
Lab
36 MJ
=
Power
× Time
=
5000 J/s
Home
=
5kW
× 7200
s
× 2hr
10 kWh
5,000J
15,000J
10,000J
Energy transferred (J, kWh) = power (W, kW) x time (s, h)

35.

Calculating the total energy transferred by
an appliance
Calculate the energy transferred by a 60W bulb that is
turned on for….
A): 20s
B): 5 min
A): E =
B): E =

36.

Calculating the total energy transferred by
an appliance
Calculate the energy transferred by a 60W bulb that is turned
on for:
•A): 20s
•B): 5 min
•A): E = 60 × 20=1200J
•B): E = 60 × 5 × 60=18000J=18kJ

37.

E = P x t
Calculate the energy transferred by a 60W bulb that is switched on for
3 minutes.

38.

E = P x t
Calculate the power of a bulb that transfers 800J of energy in 120s.

39.

E = P x t
Calculate the how long a 270W TV was switched on for if it transferred
600J of energy.

40.

Direct Current
Draw an oscilloscope screen representation of 1.5
volts D.C. – show your drawing on camera!

41.

Alternating Current
If the current constantly changes direction, it is called
alternating current, or a.c.. Mains electricity is an a.c. supply,
with the UK mains supply being about 230V. It has
a frequency of 50Hz (50 hertz), which means it changes
direction, and back again, 50 times a second. The diagram
on the next slide shows an oscilloscope screen displaying
the signal from an a.c. supply.

42.

Alternating Current

43.

Power Source
Draw one circuit diagram to represent a d.c. circuit and
another to represent an a.c. circuit. On each diagram
indicate the source of the power.
Show drawings on camera or screenshare!

44.

The Heating Effect of a Current
A wire will heat up as a current passes
through it.
Energy is transferred from the wire to
the thermal store of the surroundings.
The heat produced depends on the
resistance of the wire.
The greater the resistance, the greater
the heat.
44

45.

Uses of The Heating Effects of Current
The heating effect of electric current is used in electrical
appliances like electric heater, electric iron, electric room
heater, immersion heater, electric kettle, hair dryer etc.
All these appliances have a coil of wire called an element.
When electric current flows through the element it becomes hot
(energy is transferred to the surroundings as heat).
The amount of heat produced in a wire depends upon its
material, length and thickness.
Electric heater
Electric room heater
Electric iron
Electric kettle