NCEA Level 3 Science (90732) 2011 — page 1 of 3
Assessment Schedule – 2011
Science: Describe selected properties and applications of EMR, radioactive decay, sound
and ultrasound (90732)
Evidence Statement
Q
ONE
Evidence
14
C ® 147 N + –10b
6
14 / 0.014 = 1000 = 210 approx.
No. ½ lives = 10 approx.
10  5730 = 57 300 years approx.
• 14C enters organic tissue via the
food chain from environmental
14
C.
• Because the initial sample rate /
size is very small, any
contamination from atmospheric
14
C will affect sample. The sample
should give accurate results up to
10 half-lives; this age is at the
outer limits of being valid.
OR
• 14C enters organic tissue via the
food chain from environmental
14
C. At any one time, the
proportion of 14C in the
atmosphere is relatively stable.
However, the relative proportion
of 14C in the atmosphere has
changed with time. Because the
proportion of 14C in the
atmosphere has changed, this
needs to be taken into account and
may not have been 14
disintegrations per minute when
the sample was living. This may
make the age calculated to be not
valid if modern day initial rates
are used without calibration.
Achievement
14
C behaviour is
described by any
two of;
Equation
Age of 57 300
No. ½ lives
A description of
14
C entry into
living organisms,
eg enters the food
chain through
photosynthesis
Achievement with
Merit
Achievement with
Excellence
Equation and Age
correct with an
explanation of the
half life calculation
Eg:
14 / 0.014 = 1000
= 210 approx.
Therefore no. ½
lives = 10 approx.
Equation correct and Age
of sample given with an
explanation
AND
Evaluation is made of
accuracy of dating method
for samples this old
Eg: This value may be
inaccurate because the
amount of 14C in the
sample is very small. This
means there could be
atmospheric
contamination of the
sample. This age is the
limit of accuracy.
NCEA Level 3 Science (90732) 2011 — page 2 of 3
TWO
Doppler diagram
Eg:
• The direction is determined by
whether the received frequency is
higher or lower than the
transmitted frequency. The object
moving towards will return a
higher frequency, and the object
moving away will return a lower
frequency. This occurs because as
the car is moving towards the
radar, the reflected wave fronts are
compacted which leads to a
smaller apparent wavelength.
Because
v = fλ, if v stays the same and λ is
smaller, then f is higher.
• The speed is determined by the
relative change in frequency of the
received signal and the transmitted
signal. The fast object will have a
more compaction of the wavefronts, and therefore smaller
wavelength, hence higher change
in frequencies than a slower
object.
THREE
• A gel is used to match the relative
transmission of the transducer and
the skin to prevent reflection from
the skin.
• Bones and other tissues reflect the
ultrasound waves. Pulses are used
to prevent the outgoing and
incoming waves superimposing
and interfering with each other.
• Reflections occur at the boundaries
of tissues. Where two different
tissues have large differences in
their acoustic impedance, a clear
echo is produced. If the acoustic
impedances are similar, a weaker
echo is produced.
• Short wavelength (high frequency)
signals produce better detail
images. But if the frequency is too
high / wavelength too short, small
objects such as cells can scatter
the echoes and cause background
noise that can obscure the main
signal. This is the Rayleigh effect.
OR
Description is
given of the
compression effect
of the Doppler
wave compaction
The wave
recordings are
described in terms
of detecting
differences of
absorption or
reflection at tissue
boundaries
Eg: A gel is used to
stop the reflection
of the ultrasound
from the skin.
OR
Reflections occur
at the boundaries of
tissues.
Doppler diagram
and an explanation
is given of how
speed or direction
may be calculated
using Doppler
principles
Doppler diagram and a
comparison is made of the
recordings that would be
received when a car is
moving fast or slow and
towards or way from the
detector
Eg: The speed is
worked out by
comparing the
frequencies of the
transmitted and
received signal. A
fast object will
compact the waves
more than a slower
object. This will
result in a higher
frequency of the
received signal.
Eg: When comparing the
frequencies of the
transmitted and received
signal, a fast object will
compact the waves more
than a slower object and
an object moving towards
the radar will return a
higher frequency. This is
because as the car moves
towards the radar, the
waves are compacted up,
which leads to a shorter
wavelength, therefore a
higher frequency.
An explanation of
the need to use
pulses AND
acoustic impedance
is explained.
Eg: Pulses are used
to stop interference
from the outgoing
and the ingoing
waves. If it was a
continuous signal,
then the waves
would interfere.
AND
The reflection of
waves occurs
where there is a
boundary of tissues
and if the two
different tissues
have large
differences, then a
clear echo is
produced; if they
are similar, then a
weaker echo is
produced.
Evaluation of techniques
to improve clarity of
image is discussed
Eg: A pulse is used rather
than a continuous signal
because the interference
could result in the waves
adding together and
making the signal larger,
or they can cancel each
other out and result in a
reduced signal coming
back. A high frequency is
used because it will have a
short wavelength which
produces a clearer image.
NCEA Level 3 Science (90732) 2011 — page 3 of 3
Judgement Statement
Achievement
Achievement with Merit
Achievement with Excellence
2A
2M
2E