Exemplar for internal assessment resource Science for Achievement Standard 90941
a
Exemplar for Internal Achievement Standard
Science Level 1
This exemplar supports assessment against:
Achievement Standard 90941
Investigate implications of electricity and magnetism for
everyday life
An annotated exemplar is an extract of student evidence, with a commentary, to explain key
aspects of the standard. These will assist teachers to make assessment judgements at the
grade boundaries.
New Zealand Qualification Authority
To support internal assessment from 2014
© NZQA 2014
Exemplar for internal assessment resource Science for Achievement Standard 90941
Grade Boundary: Low Excellence
1.
For Excellence, the student needs to investigate, comprehensively, implications of
electricity and magnetism for everyday life. This involves providing reasons that clearly
explain the science that is involved, and linking those reasons to an issue that students
encounter in their everyday lives. The reasons and links should take into account both
series and parallel circuits.
The student has comprehensively investigated and discussed the types of electrical
circuits used in houses (1). The implication for society has been comprehensively
explained, with reasons for parallel circuits (2).
For a more secure Excellence, the student would need more evidence to fully link the
science to the implication(s) for society. For example, the student could discuss more
fully the reasons that series circuits are used in household electricity.
© NZQA 2014
Student 1: Low Excellence
AS 90941
Student 1
For this investigation my group investigated how resistance changes when another bulb is
plugged into the circuit. And also how resistance and current are linked and how it can be
dangerous and prevented in household conditions. The data we got is an example of a
household situation. We had 3 different bulbs to resemble 3 different appliances. Bulb 1=
12V 12W, Bulb 2 = 12V 18W, bulb 3 = 12V 12W.
From our data we know that the resistance of each circuit changed as another bulb was
added. The resistance decreased. This is because as another branch is added to the circuit
the electrons have another path to “choose from.” The resistance decreases because there
is less electrons passing through each appliance (bulb) and it is easier for them. It is seen
from our data with 1 bulb the resistance was 13.95 Ω. Add a second bulb the resistance
drops to 5.75 Ω and add the third bulb the resistance drops to 3.1 Ω.
Because the total resistance decreases as more bulbs are added it means more current is
flowing. This is because it is “easier” for the electrons to flow as there is little resistance to
stopping them. So when total resistance decreases the total current flowing increases.
In the investigation you will see the voltage decreases a small amount in the 3 circuits. 12V
were being supplied but as more bulbs were added it dropped to 11.5V because some
voltage was lost on the wires. (1)
We can say having all 3 bulbs plugged in was not safe because the amps went from 3 amps
with one bulb to 3.6 A with 3 bulbs. This was unsafe. Due to having the circuit breaker after a
few minutes it cut off. Dangerous.
A safety feature we used in our circuit was a circuit breaker. A circuit breaker is always wired
in series because when the circuit breaker trips it takes out the total circuit. The circuit
breaker was a bi-metallic strip which acted as a thermostat that when the circuit got hot
because of the amount of current broke the circuit. Circuit breakers can be used at home as
can fuses. (2)
Exemplar for internal assessment resource Science for Achievement Standard 90941
Grade Boundary: High Merit
2.
For Merit, the student needs to investigate, in depth, implications of electricity and
magnetism for everyday life. This involves providing reasons for the way science is
linked to an issue that students encounter in their everyday lives. The reasons and
links should take into account both series and parallel circuits.
The student has investigated in depth the science of parallel and series circuits (1). The
implication for society has been explained in depth, with reasons for why parallel
circuits are used in houses (2).
To reach Excellence, the student would need to comprehensively explain series
circuits, and show a comprehensive awareness of how household circuits are wired.
For example, the student could explain when parallel circuits should be used.
© NZQA 2014
Student 2: High Merit
AS 90941
Student 2
From my results I noticed that: Voltage being received by the resisters in the circuits was the
same as the total voltage supplied. This is typical of parallel circuits even though current
increases across the parallel branches. The energy carried by the electrons is the same.
Current, unlike voltage raised between circuits. The current drawn by a resistor depends on
its resistance (Ohms Law states that resistance is inversely proportional to current) Low
resistance has high current and vice versa. The order of circuits has no effect on the results.
Ohms law states that the heat in wires is directly proportional to the current flowing. More
current hotter wires. If current is very high insulation can melt and start a fire.
Application of results to a house hold environment:
In a house circuits are wired in parallel so as all branches of a circuit get 240V. It also means
a single branch can operate independent of the other branches. All components get the max
voltage. In NZ this is 240V. The problem comes with current. In parallel circuits as more
appliances are added to a circuit then more current flows and more current means a hotter
environment. If enough appliances are added to a parallel circuit then the wires get hot
enough to melt the insulation then start a fire. (1) To stop this we add circuit breakers to the
circuit at the start and this circuit breaker is wired in series. If too much current flows then the
circuit breaker trips taking out all the parallel circuits until the problem is fixed. (2)
The use of multiboxes today compounds this issue so the safest multiboxes are those with
inbuilt circuit breakers. They stop people overloading the multiboxes.
Exemplar for internal assessment resource Science for Achievement Standard 90941
Grade Boundary: Low Merit
3.
For Merit, the student needs to investigate, in depth, implications of electricity and
magnetism for everyday life. This involves providing reasons for the way science is
linked to an issue that students encounter in their everyday lives. The reasons and
links should take into account both series and parallel circuits.
The student has investigated the science of parallel circuits (1). The implication for
household electricity has been explained (2). The role of series circuits in making
circuits safe has been mentioned.
For a more secure Merit, the student could explain series circuits in greater depth, and
link the explanation to how houses are wired, especially in relation to electrical safety.
© NZQA 2014
Student 3: Low Merit
AS 90941
Student 3
Parallel circuit is a circuit where 2 or more path ways for electrons to pass through and go to
the power user and all the power user gets all voltage from the power source whereas in a
series circuit there is only one path way for the electrons to go through and if there is two or
more power users in the series circuit. (1) Those two power uses will have to share the
voltage that the power supply is giving meaning dimmer lights and inappropriate in a home
where all bulbs are equally bright in a parallel and can have multiple switches to control
individual lights which makes it very good in the home environment. However having too
many appliances will mean the current also increases due to more appliances pulling out
certain amount of amps from the power source which can then produce heat in the wires and
burn the insulator of the wire and burn the house down but normally we would have a fuse to
prevent this from happening. (2) The fuse will act as a circuit breaker by burning the metal
piece in it and causing the metal to bend away from it cutting the electrical current. This type
of breaker is not used in houses because they turn circuits off and on all the time and this
can damage appliances. Today we use a magnetic circuit breaker where to much current will
magnetise the metal in the wire holding on to the electrons. According to the data I collected
there is a connection between resistance and current. When resistance is high current is low
and the opposite.
Exemplar for internal assessment resource Science for Achievement Standard 90941
Grade Boundary: High Achieved
4.
For Achieved, the student needs to investigate implications of electricity and
magnetism for everyday life. This involves showing awareness of how science is linked
to an issue that students encounter in their everyday lives. The awareness and links
should take into account both series and parallel circuits.
The student has investigated parallel and series circuits (1) and shown an awareness
of how both types of circuits are used in household wiring (2).
To reach Merit, standard the student could explain in greater depth parallel and series
circuits and link the explanation how they are used to wire a house.
© NZQA 2014
Student 4: High Achieved
AS 90941
Student 4
In the gathering data stage our group had 5 circuits to make up. In a series circuit the total
amount of resistance increases as more components are added. Although the circuits we
used in our set-up and most of the circuits used at home are parallel circuits. In a parallel
circuit the total amount of the resistance decreases as more components are added and as
a result of the resistance decreasing the total amount of current that can flow through the
circuit increases. (1) Circuit 1 had only 1 component and a total resistance of 14.29Ω and a
current of 0.48A. This was the highest total resistance and lowest current. With 3 bulbs
linked in parallel the resistance dropped to 5.68Ω and the current increased to 1.22A. This
showed the more components we added resistance decreases and current increases. (Any
changes in the voltage were minor and so we suggest voltage does not change and the
difference was due to poor equipment.)
The heat of the circuit is directly proportional to the amount of current passing through the
circuit – that is that the more current that flows the hotter the circuit gets. So in the home
environment plugging in a lot of appliances into the same power source could start a fire.To
prevent this we can use a fuse (olden days) or a circuit breaker (modern days). (2)
Exemplar for internal assessment resource Science for Achievement Standard 90941
Grade Boundary: Low Achieved
5.
For Achieved, the student needs to investigate implications of electricity and
magnetism for everyday life. This involves showing awareness of how science is linked
to an issue that students encounter in their everyday lives. The awareness and links
should take into account both series and parallel circuits.
The student has investigated parallel and series circuits (1) and shown some
awareness of an implication for society (2).
For a more secure Achieved, the student could describe parallel and series circuits,
and link the descriptions to show an awareness of how they are used to wire a house.
© NZQA 2014
Student 5: Low Achieved
As 90941
Student 5
Electricity is used everywhere in our houses and is used in our everyday lives. There is
current (Amps) and voltage (volts) involved in electricity. In our homes there is circuits that is
connected to the back of the wall. These circuits are in parallel where you can plug lots of
appliances into one plug. Running in these wires are current flowing. The more current there
is the brighter the lights or the more energy there is. But when there is too much current
flowing all at once too much energy and power is being used up in the house then the wires
heat up and catch fire. With too many appliances connected in parallel and series the metal
heats up and melts and the molten metals starts a fire. A fuse then turns off or on when
there are too much watts (power) being supplied in the house. This happens because of too
much power and current flowing at the same area of the house.(1)] Fuses or circuit breakers
are used in homes so that not too much electricity flow and blow up the bulbs. Plugging an
additional appliance is dangerous because if you are putting a lot of plugs onto one power
socket. You never know how much current or power flows in that socket to produce energy.
(2)
For safety you need to plug appliances into one series circuit for a period of time. Power
should be the largest number of because Watts is how many power is wasting. For example
if I left the microwave on with a pie in it for 20 minutes the pie would be burnt and not only
that the wrapper would be damaged. A lot of current flows in microwaves. I suggest the
circuit breaker is placed at the start of a circuit, near the wall plug to slow down currents.
Current always starts near a plug so this is why the circuit breaker or fuse goes here. Fuses
should never be connected here.
Exemplar for internal assessment resource Science for Achievement Standard 90941
Grade Boundary: High Not Achieved
6.
For Achieved, the student needs to investigate implications of electricity and
magnetism for everyday life. This involves showing awareness of how science is linked
to in an issue that students encounter in their everyday lives. The awareness and links
should take into account both series and parallel circuits.
The student has investigated parallel circuits only (1).
To reach Achieved, the student could clearly describe the science behind parallel and
series circuits and show an awareness of how they are used to wire a house.
© NZQA 2014
Student 6: High Not Achieved
AS 90941
Student 6
It is relatively safe to connect multiple components of high resistance in a circuit as each
component only draws low current. Adding additional branches in a parallel circuit provides
an alternative pathway for the electrons to flow. Having an alternative pathway causes
different currents to flow in each path, but it would be dangerous when there are two or more
components of high current and low resistance. The more circuits and less resistance there
is there’s a chance the wires could be hot. The heating effect is called directly proportional,
that is where the wire gets hot and might cause fire emergencies. The wire has copper and
plastic to avoid it from heating up. Also a circuit breaker or a fuse is also used to limit the
amount of current flowing in the circuit. In our test circuit the circuit breaker went off at A4.
Adding resistance in a parallel circuit lowers the total resistance of the circuit which heats up
the circuit. As you add additional components in a circuit the dimmer the bulbs resistance
would be. Also the resistors share the voltage. Also in parallel you have to be careful
because the voltage is much higher. Parallel circuits are much more expensive than series
circuits and also they are more dangerous(1). To prevent accidents we make circuits safe
like avoiding energised electricity or keeping one hand in your pocket when plugging in a
plug.