8.3 Electrical Energy in the Home

brothersroocooElectronics - Devices

Oct 18, 2013 (3 years and 7 months ago)

110 views

Electrical Energy in the Home

Preliminary Module 8.3

1

8.3

Electrical Energy in the Home


Contextual Outline

Electricity is an essential energy source for modern living. Disruption to supply or isolation can lead to the development
of alternative methods of obtaining this essential energy resource. For electri
cal energy to be useful it must be
harnessed through the use of an electrical circuit and an energy
-
converting appliance.


As electricity became increasingly used as the main power supply in homes and electrical appliances became an
integral part of daily
life for many Australians, the dangers associated with electricity became more prominent. Voltages
as low as 20 volts can be dangerous to the human body depending on the health of the person and length of time of
contact with the current. Safety devices in

household appliances and within the electric circuits in the home can prevent
electrical injury or assist in reducing the potential for electric shock.


This module increases students’ understanding of the history, nature and practice of physics and the a
pplications and
uses of physics.


Assumed Knowledge

Domain: knowledge and understanding:


Refer to the
Science Stages 4

5 Syllabus

for the following:

5.6.3a

design, construct and draw circuits containing a number of components

5.6.3b

describe voltage, resi
stance and current using analogies

5.6.3c

describe qualitatively, the relationship between voltage, resistance and current

5.6.3d

compare advantages and disadvantages of series and parallel circuits



Physics PFAs (from table 7.1) in this module of work

P
1.

outlines the historical development of major principles,
concepts and ideas in physics

Major concepts



Energy transformations



Energy transfer


including reflection, refraction



Electric and magnetic fields



Production of magnetic field by an electric curr
ent (Oersted)

P2.

applies the processes that are used to test and validate
models, theories and laws of science with particular
emphasis on first
-
hand investigations in physics

Models:

electric and magnetic fields

Theories:

Atomic theory,

Laws:

Ohm’s law
, Law of conservation of energy, Kirchov’s
current and voltage laws (not required by name, but
the principal must be understood)

P3.

assesses the impact of particular technological advances
on understanding in physics



Development of electrical meters

P4.

describes applications of physics which affect society or
the environment



Use of electricity for lighting and heating homes



Use of electricity to light streets in towns/cities



Use of electricity to allow factories to operate 24 hours a
day (a radical indu
strial change in the early 20
th

C)



Use of magnetism


motors and generators

P5.

describes the scientific principles employed in particular
areas of research in physics



Discuss


In the following table, the two columns on the left correspond to columns 2 a
nd 3 in the
syllabus document. Contextual information from column one of the syllabus has been included
in column 1 of the table below.
Electrical Energy in the Home

Preliminary Module 8.3

2


1.

Society has become increasingly
dependent on electricity over the
last 200 years








identify data sources, gather,

process
and analyse secondary information
about the differing views of Volta and
Galvani about animal and chemical
electricity and discuss whether their
different views contributed to increased
understanding of electricity

1.

Compare the views of Volta and
G
alvani about the nature of electricity.
(3M)

2.

Outline the contribution of Galvani to
the development of major ideas about
electricity. (2M)



discuss how the main sources of
domestic energy have changed over
time




3.

Use a timeline to present information
about
the sources of energy for
homes. (5M)



assess some of the impacts of changes
in, and increased access to, sources of
energy for a community




4.

Assess the impacts of changes in, and
increased access to, sources of
energy for a community. (5M)



discuss some of

the ways in which
electricity can be provided in remote
locations




5.

Discuss how electrical energy can be
provided to remote locations on the
Earth. (6M)

6.

Discuss the provision of electrical
energy on an interplanetary satellite.
(4M)

2.

One of the main adv
antages of
electricity is that is can be moved
with comparative ease from one
place to another through electric
circuits





describe the behaviour of electrostatic
charges and the properties of the fields
associated with them



present diagrammatic informati
on to
describe the electric field strength and
direction:



between charged parallel plates



about and between a positive and
negative point charge

7.

Identify a factor other than distance
that affects the magnitude of the force
between two charges.

8.

Describe th
e nature of the force,
including the effect of distance,
between two positive charges. (2M)

9.

Draw the electric field surrounding a
positive charge. (2M)

10.

Compare the electric field surrounding
a positive charge with the field
surrounding a negative charge. (
2M)

11.

Draw the electric field surrounding two
equal but opposite charges near each
other. (2M)

12.

The behaviour of electrostatic charges
is based on a model in which there are
two types of charge. Outline the
experimental evidence that supports
this model. (2M)

[P2]

13.

Michael Faraday first proposed the
concept of a “force field”. Describe the
relationship between the field model
and the observed behaviour of electric
charges. (3M) [P2]



define the unit of electric charge as the
coulomb




14.

Name the symbol for electri
c charge
and write the symbol for that unit.



define the electric field as a field of
force with a field strength equal to the
force per unit charge at that point:



solve problems and analyse information
using:

15.

Calculate the electric field strength at
a point if a charge of 2 microcoulombs
experienced a force of 6
Electrical Energy in the Home

Preliminary Module 8.3

3



nanonewtons.

16.

Calculate the force that would be
produced on an electron in a cathode
ray tube in which the electric field
strength was 200 000 N C
-
1
.

The electron charge is
-
1.6

x

10
-
19

C.



identify the difference between
conductors and insulators



gather and process secondary
information to identify materials that are
commonly used as conductors to
provide household electricity

17.

Contrast conductors and
insulators,
using an example of each to clarify
your answer. (3M)

18.

Identify the two metals most
commonly used to conduct electricity
to household users.



define electric current as the rate at
which charge flows (coulombs/ second
or amperes) under the infl
uence of an
electric field




19.

Electric current is defined as the rate
of flow of charge in a circuit. Write this
definition using symbols for the
quantities involved and state the SI
units for these quantities. (4M)

20.

Calculate the current in a household
heate
r through which 600 coulombs of
charge is passing every minute.

21.

Explain why an electric current flows
through a wire connected to a battery.
(3M)



identify that current can be either direct
with the net flow of charge carriers
moving in one direction or al
ternating
with the charge carriers moving
backwards and forwards periodically




22.

Identify the charge carriers
responsible for the flow of electric
current in (a) a copper wire (b) a salt
solution (c) an ionised gas e.g. neon

23.

A light bulb was connected to a b
attery
using alligator clip leads. Outline the
nature of the electric current through
the light bulb. (2M)

24.

Outline the nature of the electric
current through a domestic appliance
such as an electric toaster or kettle.
(1M)



describe electric potential dif
ference
(voltage) between two points as the
change in potential energy per unit
charge moving from one point to the
other (joules/coulomb or volts)


25.

Identify the unit used to measure
energy. (1M)

26.

Define the volt beginning the definition
“The volt is the p
otential difference
between two points when the work
done…” (1M)

27.

A ‘D’ battery produces a potential
difference of 1.5 volts across its
terminals. How much energy is used
when 4 coulombs of charge flows
through lamp connected to a ‘D’
battery? (1M)

28.

Calculat
e the energy produced per
hour by the lamp in the adjacent
circuit. (4M)

3.

Series and parallel circuits serve
different purposes in households







identify the difference between series
and parallel circuits




29.

Draw diagrams to show two lamps
connected to a

battery (a) in series
(b)

in parallel. (2M)

30.

Describe verbally the difference
between a series circuit and a parallel
circuit. (2M)

Electrical Energy in the Home

Preliminary Module 8.3

4



identify uses of ammeters and
voltmeters




31.

Tabulate for an ammeter and
voltmeter the quantity each is used to
measure, symbo
l for the quantity, the
unit used to measure the quantity and
the symbol for the unit. (4M)



explain why ammeters and voltmeters
are connected differently in a circuit

Fig. (a)

Photograph of wrong circuit


Fig. (b)



Fig. (c)

Photo of correct circuit


3
lamps 2
meters

32.

Ammeters must be connected in
series with the device through which
they are measuring the current.
Explain why ammeters ideally have a
zero
resistance
. (2M)

33.

Draw a circuit diagram to show an
ammeter wired to measure (a) the
current through a

circuit with two
lamps in series with a battery.

34.

Draw a circuit diagram showing an
ammeter connected to measure the
current through one of two lamps
connected in parallel in a circuit.

35.

Draw a circuit diagram to show a
voltmeter wired to measure the
voltag
e across one of two lamps in
series with a battery.

36.

Draw a circuit diagram showing a
voltmeter connected to measure the
voltage across one of two lamps
connected in parallel in a circuit.

37.

Identify the fault in the circuit shown in
the photograph in figure
(a) xxx

38.

Draw a circuit diagram to represent the
circuit shown in the photograph in
figure (c).

39.

A student wired the adjacent circuit
and observed that the lamp did not
light up but that there was a reading
on the meter. Explain the observations
and draw a d
iagram to show how the
meter should have been connected
with the battery and light globe. (4M)



compare parallel and series circuits in
terms of voltage across components
and current through them



plan, choose equipment or resources
for and perform first
-
ha
nd investigations
to gather data and use available
evidence to compare measurements of
current and voltage in series and
parallel
circuits in computer simulations

or
hands
-
on equipment

40.

Compare the currents through two
identical light globes placed in serie
s
and then in parallel across the same
voltage source. (3M)

41.

Compare the voltages across two
identical light globes placed in series
and then in parallel across the same
voltage source. (3M)

42.

A low
-
wattage lamp and a high
-
wattage lamp were placed first in
se
ries and then in parallel across a
voltage supply. (a) Compare their
brightness in each circuit (2M)
(b)

Compare the currents through
them in both circuits. (4M)



explain why there are different circuits
for lighting, heating and other
appliances in a hous
e



plan, choose equipment or resources
and perform a first
-
hand investigation to
construct simple model household
circuits using electrical components

43.

With reference to the appliances
connected to the circuits, explain why
there are different electrical cir
cuits in
a house. (5M)

44.

Use a diagram to show how one circuit
is used in a house to independently
operate the lights in three separate
Electrical Energy in the Home

Preliminary Module 8.3

5

rooms. (2M)

45.

Propose two reasons why a series
circuit would not be suitable to operate
the lights in two rooms of a house.
(2M)



discuss how potential difference
changes between different points
around a DC circuit



plan, choose equipment for and perform
a first
-
hand investigation to gather data
and use the available evidence to show
the variations in potential difference
betwe
en different points around a DC
circuit

46.

A series circuit was constructed using
two unequal lamps and a 12 volt
battery. The voltage across one of the
lamps was 4 volts. (a) In an ideal
circuit, predict the voltage across the
other lamp. (1M). (b) The gener
al law
upon which your answer is based is
called Kirchoff’s voltage law. State this
law. (2M)

47.

A parallel circuit was constructed
using two unequal lamps and a 12 volt
battery. The current through one of the
lamps was 0.5 A and the total current
from the ba
ttery was 0.75 A. (a)
Predict the current through the other
lamp. (1M). (b) Explain the . (2M)




plan, choose equipment for and perform
a first
-
hand investigation to gather data
and use the available evidence to show
the relationship between voltage acros
s
and current in a DC circuit

48.

Draw a circuit diagram of the circuit
required to investigate the relationship
between voltage the across and the
current through a resistor in a DC
circuit. (3M)

49.

Calculate the resistance of the resistor
for which the voltage
-
current data has
been graphed (left). (2M)

50.

Identify the independent and
dependent variables in the
investigation you conducted into the
voltage
-
current relationship. (2M)



define resistance as the ratio of voltage
to current for a particular conductor:




solve problems and analyse information
applying:


51.

Calculate the resistance of a resistor
through which the current was 0.5 A
when the applied voltage was 20 V.

52.

A lamp had a current of 3 A through it
when a voltag
e of 12 V was applied.
What was the resistance of the lamp?

53.

A voltage of 6 V was applied across a
100 ohm resistor. Calculate the
current that flowed through it. (2M)

54.

Assess how the development of
electrical meters has advanced our
understanding of physics
. (3M) [P3]



describe qualitatively how each of the
following affects the movement of
electricity through a conductor:



length



cross sectional area



temperature



material




55.

Two pieces of aluminium wire differ
only in their lengths, one being three
time
s the length of the other. Compare
the resistance of the two wires. (2M)

56.

Compare the electrical resistance of
two copper wires of the same length if
one has three times the diameter of
the other. (2M)

57.

Two pieces of copper wire have the
same resistance. One

is nine times
the length of the other. Propose one
reason that could account for this.
(2M)

58.

Outline the effect of temperature on
Electrical Energy in the Home

Preliminary Module 8.3

6

the conductivity of a metal. (1M) [HSC]

59.

Account for the change in the
resistance of a metal as temperature
increases. (3M) [HS
C]

60.

Account for different metal conductors
being used in the supply of domestic
electricity. (2M)

61.

Two pieces of electrical wiring have
the same resistance. One is nine
times the length of the other. Propose
two reasons that could account for
this. (2M)

4.

The amount of power is related to
the rate at which energy is
transformed





explain that power is the rate at which
energy is transformed from one form to
another




62.

Define

the term “power”. (1M)

63.

Write the definition for power using
symbols to represent the

quantities
and identify the SI units and the
abbreviations for these units. (4M)

64.

In one hour, an electric kettle converts
6.4 megajoules of electrical energy
into heat. Calculate the power of the
kettle. (2M)



identify the relationship between power,
pote
ntial difference and current




65.

Write the relationship between power,
voltage and current using symbols to
represent the quantities and identify
the SI units and the abbreviations for
these units. (4M)



identify that the total amount of energy
used depends o
n the length of time the
current is flowing and can be calculated
using:

Energy = VIt




66.

Manipulate the equations for electrical
power and the definition of power to
show that the electrical energy used
by an appliance is equal to VIt. (2M)

67.

Identify the SI
units and symbols for
the units in the equation E = VIt. (4M)






solve problems and analyse information
using:

P=VI

and

Energy = VIt

68.

When a particular 240 V electric
toaster is being used, a current of 8.33
amperes flows through it. Calculate its
power. (2M
) [2000 W]

69.

Compare the currents through a 60 W
240 V incandescent light globe and a
60 W 12 V light globe. (3M)

70.

Compare the energy used to operate a
120 W television for 4 hours with the
energy required to operate a 2400 W
room heater for half and hour.



e
xplain why the kilowatt
-
hour is used to
measure electrical energy consumption
rather than the joule




71.

Identify the SI unit for energy, and the
abbreviation for that unit. (2M)

72.

Convert 1 kWh to joules. (2M)

73.

Compare the cost of energy obtained
from gas and el
ectricity if xxxx kWh of
electricity costs $xxxx and xxxx MJ of
energy obtained from gas costs $xxxx.
(4M)

74.

Using the figures from the previous
question to justify your answer,
propose whether it is in the best
interests of the electricity company or
the ga
s company to have different
Electrical Energy in the Home

Preliminary Module 8.3

7

bases for charging for the energy used
by a household.






perform a first
-
hand investigation,
gather information and use available
evidence to demonstrate the
relationship between current,
voltage
and power for a model

6V to 12V
electric
heating coil

75.

A group of students investigated the
electrical energy generated in a coil
submerged in water and the heat
energy gained by the water. The
electrical energy was 2500 J and the
heat energy determined from the
temperature change of the
water was
2000 J. Assess this result and account
for the differences between the two
quantities. (6M)

5.

Electric currents also produce
magnetic fields and these fields
are used in different devices in the
home





describe the behaviour of the magnetic
po
les of bar magnets when they are
brought close together




76.

Describe the behaviour of the
magnetic poles of bar magnets when
they are brought close together. (3M)



define the direction of the magnetic field
at a point as the direction of force on a
very small

north magnetic pole when
placed at that point




77.

State the convention used to specify
the direction of a magnetic field.

78.

Explain why “a very small magnet” is
specified in the process of determining
magnetic field direction. (2M)

79.

Describe the behaviour of a

bar
magnet suspended so that it is free to
rotate in the horizontal plane in the
Earth’s magnetic field. (1M)

80.

Identify the polarity of the Earth’s
magnetic pole in the Antarctic region.
(1M)



describe the magnetic field around pairs
of magnetic poles




81.

Dra
w a diagram to represent the
magnetic field associated with a bar
magnet. (3M)

82.

Draw a diagram to represent the
magnetic field in the region between
two magnetic south poles. (3M)

83.

Draw a diagram to represent the
magnetic field in the region between
two magn
etic
north

poles. (3M)



describe the production of a magnetic
field by an electric current in a straight
current
-
carrying conductor and describe
how the right hand grip rule can
determine the direction of current and
field lines




84.

Outline, with the aid of a

suitable
diagram, the historical development of
the major physical principle discovered
by Oersted. (3M)

85.

A student wanted to demonstrate the
discovery made by Oersted about
electric current and magnetism. He
stretched a long wire in an east
-
west
direction

and placed a compass
directly under the wire. He then
passes a large current through the
wire. Assess this student’s
investigation. (3M)






plan, choose equipment or resources
for, and perform a first
-
hand
investigation to build an electromagnet

86.

Outline so
me steps you would take
before making an electromagnet. (3M)

87.

Present a set of instructions, which a
person could follow to build and test a
simple electromagnet. (6M)

Electrical Energy in the Home

Preliminary Module 8.3

8



compare the nature and generation of
magnetic fields
by solenoids and a bar
magnet




88.

Comp
are the magnetic fields around a
bar magnet and a solenoid. (3M)

89.

Compare the production of a magnetic
field by a bar magnet with the
production of a magnetic field using a
solenoid. (4M)


Figure (a)



perform a first
-
hand investigation to
observe magnetic
fields by mapping
lines of force:



around a bar magnet



surrounding a straight DC

current
-
carrying conductor



a solenoid

90.

Michael Faraday first proposed the
concept of a “force field”. Describe
the relationship between the field
model and the observed behaviou
r
iron filings sprinkled around a bar
magnet. (3M) [P2]

91.

Draw a diagram to represent the
magnetic field surrounding a bar
magnet. (3M)

92.

Describe verbally the magnetic field
surrounding a straight current
-
carrying
conductor.

93.

Draw a diagram to represent the
ma
gnetic field surrounding the
solenoid shown in figure (a). (3M)
[HSC]






present information using


and

to
show the direction of a current and
direction of a magnetic field

94.

Use the symbols


and

to clarify the
nature of the magnetic field around a
stra
ight conductor carrying a direct
current. In your answer show two
views of the wire and the field, one
viewed from looking towards the end
of the wire and one in which the wire is
viewed from the side. (6M)

95.

Draw a cross
-
section of a solenoid,
showing the d
irection of the current in
the coils and the nature of the
magnetic field produced. (4M)






identify data sources, gather, process
and analyse information to explain one
application of magnetic fields in
household appliances

96.

Many household appliances make u
se
of a transformer. Outline what a
transformer does and draw a diagram
to show the three main components of
a transformer. (5M) [HSC]

97.

Identify 6 household devices that
contain an electric motor.

98.

Explain the principle of a DC electric
motor. (3M) [HSC]

99.

Des
cribe applications of electricity and
magnetism that affect society. (4M)
[P4]

6.

Safety devices are important

in household circuits





discuss the dangers of an electric shock
from both a 240 volt AC mains supply
and various DC voltages, from
appliances
, on the muscles of the body





100.

Discuss how the dangers
associated with the domestic
electricity supply are minimised. (6M)

101.

Outline what actions you would
take if you walked into a room and
found a person lying apparently
unconscious on the floor with an
el
ectric toaster with burning toast in it
on the floor next to the person. (6M)