Download Waves mock exam answers File

1
New Zealand Institute of Physics
ASSESSMENT SCHEDULE
Physics Level 2
91170 Demonstrate understanding of waves
Note: Minor computational errors will not be penalised. A wrong answer will be accepted as correct provided there
is sufficient evidence that the mistake is not due to a lack of understanding. Such evidence includes:


the last written step before the answer is given has no unexpanded brackets or terms and does not require
rearranging.
the power of any number that is multiplied by a power of 10 is correct.
Correct units and significant figures are required only in the questions that specifically ask for them.
91170 • Demonstrate understanding of waves • Assessment Schedule 2013
2
Evidence Statement
Question
One
(a)
Evidence
See appendix.
(b)
Convex mirrors produce diminished, upright
images in order to achieve the wider field of
view.
(c)
See appendix.
Calculates di=+/- 5 m
Question
(b)
Evidence
Merit
Reflected rays have
approximately equal
angles of incidence and
reflection.
Wider field of view OR
smaller images.
Draws one correct
reflected ray.
(d)
Two
(a)
Achievement
Achievement
See appendix.
One correct ray.
The image is virtual because the light rays
are not converging at the image, or the
image cannot be shown on a screen or the
image is produced on the same side of the
lens as the object.
Virtual stated.
(c)
Correct answer.
(d)
Uses positive di to
find a value for do.
Wider field of
view AND
idea that as a
consequence of
a smaller image
a wider field of
view is
produced.
Correct ray
diagram with
two or more
rays and image
shown.
One mistake
made, e.g. used
positive di, or
did not invert 1/f.
Merit
Excellence
Correct
working
and
answer.
Excellence
ONE correct focal
point and TWO
correct rays.
Virtual plus reason
– either the light
rays are diverging,
or do not converge
at the image, or the
image cannot be
shown on a screen
or image is on
same side as
object.
Correct do
OR
Correct working but
uses positive di.
Distance between object and image
91170 • Demonstrate understanding of waves • Assessment Schedule 2013
Correct
working and
answer.
3
Question
Three
(a)
Evidence
Distance travelled by light
Achievement
Merit
Calculates total
distance travelled
by light.
Correct working
and answer.
Correct frequency.
Correct period.
Excellence
Distance from earth to moon
(b)
(c)
See appendix.
(d)
The violet laser light has a shorter
wavelength than the red laser light. Shorter
wavelengths do not diffract as much as
longer wavelengths, so the band of light on
the screen will not be as wide.
(e)
See appendix for diagram.
Two circular waves come out of the two
slits and the two waves interfere. Where
two crests or two troughs meet there is
constructive interference, producing a wave
with high amplitude, meaning a bright spot.
This bright spot is called an
antinode/maximum. Between the antinodes
there are nodes/minima, where crests and
troughs meet, causing destructive
interference, causing a wave with small or
no amplitude, causing the dark spots.
Allow explanation in terms of path
difference and/or phase between waves
incident at the same place, i.e. at
antinodes: integer difference in path
difference/in phase; at nodes: path
difference of ½ wavelength/out of phase
Diffracted waves
are approximately
circular, with a
similar wavelength
to the incident
waves.
Allow part of
diffracted waves to
be straight line if in
line with opening.
Band will not be as
wide.
Diagram showing
overlapping circular
waves.
OR
Positions of
constructive
interference
produce bright light,
positions of
destructive
interference
produce no/dim
light.
OR
constructive
interference occurs
when crests and
crests overlap, and
troughs and
troughs overlap,
and destructive
interference occurs
when crests and
troughs overlap.
Band will not be
as wide since
shorter
wavelengths do
not diffract as
much as longer
wavelengths.
Diagram showing
overlapping
waves
AND ONE of
(Positions of
constructive
interference
produce bright
light, positions of
destructive
interference
produce no/dim
light.
OR
constructive
interference
occurs when
crests and crests
overlap, and
troughs and
troughs overlap,
and destructive
interference
occurs when
crests and
troughs overlap.)
91170 • Demonstrate understanding of waves • Assessment Schedule 2013
Diagram
showing
overlapping
waves and
antinodal lines
marked.
Clear link
between
crests/troughs
to
constructive/d
estructive
interference to
amplitude to
brightness.
4
Question
Evidence
Achievement
Merit
Excellence
Waves going into
glass have a
smaller
wavelength and
direction shows
bending towards
the normal.
OR
Waves going into
water have a
longer wavelength
than in glass, and
direction shows
bending away
from the normal.
Complete and
correct
diagram
including both
wavelength
and wave
direction in
both media.
Correct working
and answer.
Four
(a)
(b)
See appendix.
(c)
Total internal reflection occurs when light is
going from a medium with higher refractive
index/lower wave speed towards a medium
with lower refractive index/higher wave
speed, and the angle of incidence is greater
than the critical angle for the two materials.
Waves going into
glass have a
smaller wavelength.
OR
Direction of wave is
shown to bend
towards the normal
going into glass.
OR
Waves going into
the water have a
larger wavelength
than in glass
OR
Bending away from
the normal going
into water.
Light is going from
a medium with
higher refractive
index / low wave
speed towards a
medium with low
refractive
index/high wave
speed
OR
The angle of
incidence is greater
than the critical
angle for the two
materials.
Selects the correct
formula, but has a
minor error in
rearranging, or
reverses n1 and n2.
OR
Correct indication
o
that θc is 90 .
(d)
Light is going
from a medium
with higher
refractive index /
low wave speed
towards a
medium with low
refractive
index/high wave
speed.
AND
The angle of
incidence is
greater than the
critical angle for
the two materials.
NOTE: For merit
do not accept
“higher/lower
density”, but
“higher/lower
optical density” is
okay.
Correct working
and answer.
Judgement Statement
Achievement
Achievement with Merit
Achievement with Excellence
8AME
10AME including 5ME
12AME including 7ME of which 2E
91170 • Demonstrate understanding of waves • Assessment Schedule 2013
5
Appendix
1a
1c
Car
f
f
2a
Cell
f
Image of cell
91170 • Demonstrate understanding of waves • Assessment Schedule 2013
6
3c
3e
Antinodal lines
4b
Air
Glass
Water
91170 • Demonstrate understanding of waves • Assessment Schedule 2013