Download Outcomes Assessed

2005
Half – Yearly HSC
EXAM
Weighting: 10%
Physics
Theme:
“Jane’s Birthday Exam”.
General Instructions
 Reading time – 5 minutes
 Working time – 2 hours
 Board-approved calculators may be
used
 Write using blue or black pen
 Draw diagrams using pencil
A Data Sheet and Periodic Table, and
Formulae Sheets are provided at the
back of this paper.
Total marks (70)
Part I
This section has three parts, Part A, Part
B and Part C
Part A
Total marks (15)
 Attempt Questions 1 – 15
 Allow about 30 minutes for this part
Part B
Total marks (45)
 Attempt Questions 16-21
 Allow about 1 hour and 10 minutes for
this part
Section II – Elective Style
Part C
Total marks (10)
 Attempt Question 22
Allow about 20 minutes for this part
Part A
Total marks (15)
Allow about 30 minutes for this part
Use the multiple choice answer sheet.
Select the alternative A, B, C or D that best answers the question. Fill in the response oval completely.
Sample
2+4=
(A) 2
A
(B) 6
B
(C) 8
C
(D) 9
D
If you think you have made a mistake, put a cross through the incorrect answer and fill in the new answer.
A
B
C
D
If you change your mind and have crossed out what you consider to be the correct answer, then indicate
this by writing the word correct and drawing an arrow as follows:
A
B
correct
C
D
Outcomes Assessed
H1
H2
H3
H5
H6
H7
H8
H9
H10
H11
H12
H14
evaluates how major advances in scientific understanding and technology have changed
the direction or nature of scientific thinking
analyses the ways in which models, theories and laws in physics have been tested and
validated
assesses the impact of particular advances in physics on the development of technologies
identifies possible future directions of physics research
explains events in terms of Newton’s Laws, Law of Conservation of Momentum and
relativity
explains the effect of energy transfers and transformation
analyses wave interactions and explains the effects of those interactions
explains the effects of electric, magnetic and gravitational fields
describes the nature of electromagnetic radiation and matter in terms of the particles
justifies the appropriateness of a particular investigation plan
evaluates ways in which accuracy and reliability could be improved in investigations
assesses the validity of conclusions from gathered data and information
2- -
It was Jane's birthday, and all the fizzix students were sitting around the Souberon room drinking stuff,
relaxing from their exams.
Question 1
'I wish I could go into space' said Lucy. 'It would be fun to be weightless in orbit'. This is because
(a)
(b)
(c)
(d)
all gravity forces are balanced out.
objects in orbit are falling.
there is no gravity in space.
the centripetal force is cancelled out by the centrifugal force.
Question 2
'Yeah, this guy I studied was the first to launch a liquid fuel-based rocket that could get you into space' said
Lei. The guy's name is
(a)
(b)
(c)
(d)
Oberth
Esnault-Pelterie
Goddard
von Braun
[N.B. I couldn't spell Tsiolkovsky so I didn't include him in the question - Mr. N.]
Question 3
Georgia then said 'When we were at the Powerhouse museum, I played this game about launching a rocket
- I crashed it many times on purpose, heh, heh.' What Georgia should have done to get the rocket into orbit
was to
(a)
(b)
(c)
(d)
balance the thrust force against the weight force of the rocket.
calculate the total energy needed to achieve a particular orbit.
calculate the impulse given to the rocket by the fuel and (Lucy, you’ll love this) created a
differential equation showing how to maintain a constant thrust as the rate mass of the
rocket decreases.
not used the simulation in the first place because it was too childish.
Question 4
'Well then, what orbital speed should I use to keep the spacecraft at 200 km altitude if the radius of the
Earth is 6380 km?' demanded Georgia, trying to avoid doing maths, but also amazed that she remembered
the radius of the earth. Lucy immediately pulled her calculator and obtained the correct value of
(a)
(b)
(c)
(d)
2.07 km/sec
8.03 km/sec
11.4 km/sec
27.3 km/sec
3- -
Question 5
'But what do you need to get into space?' asked Lei. Jane correctly answered: “To save fuel and get the
fastest speed quickly, you need to move
(a)
(b)
(c)
(d)
east to west along the equator.”
west to east along the equator.”
south from the North pole.”
north from the South pole.”
Question 6
“Hey, but it’s more fun seeing the spaceship burn up on re-entry” said __________ (Come on, who else
would want to see spaceships burning up…?). A spaceship would generate large amounts of heat on reentry due to
(a)
(b)
(c)
(d)
a steep entry angle and friction with the air.
a steep entry angle and a compression of the air column below it.
a shallow entry angle and friction with the air.
a shallow entry angle and a compression of the air column below it.
Question 7
'But I want to go faster than a chemical rocket. I want to feel the rush of aether on my face; I want to meet
my identical twin when she is 100 years older than me; I want to feel the shockwave from a supernova
explosion before the star blows up!' Jane said. The concepts Jane had in mind were, in order
(a)
(b)
(c)
(d)
simultaneity, the twin paradox and a nineteenth century idea about the medium for light.
a nineteenth century idea about the medium for light, the twin paradox and simultaneity.
the twin paradox, a nineteenth century idea about the medium for light and simultaneity.
the twin paradox, simultaneity and a nineteenth century idea about the medium for light.
Question 8
'I can't watch my favourite movies in space'' Georgia exclaimed.
'Not so,' said Lucy 'there are many cathode ray tubes on the older Russian spacecraft, but they all have the
same basic design:”
D
B
A
C
The parts labelled A, B, C, D are respectively
(a)
(b)
(c)
(d)
anode accelerator, electrostatic deflector, electromagnetic deflector, heating filament.
anode accelerator, electromagnetic deflector, electrostatic deflector, electron gun.
heating filament, anode accelerator, electrostatic deflector, electromagnetic deflector.
heating filament, anode accelerator, electromagnetic deflector, electron gun.
4- -
Question 9
'Here, let me show you a calculation...' Lucy said. 'If the voltage on the electrostatic deflector is 28000V
and it is separated by 6 cm, and the magnetic field is 0.23 T as shown, then the speed of the undeflected
electrons is...'
V = 28 000 V
X X X X X Magnetic Field 0.23T into the page
electron
X X X X X d = 6 cm
X X X X X
(a)
(b)
(c)
(d)
1.03 X 102 m/s
5.08 X 104 m/s
1.02 X 105 m/s
2.03 X 106 m/s
Question 10
'But the spacecraft will also need solar cells.' said Lei. “Without these, you won’t get a picture on the
screen. Hey, didn’t Albert (Einstein) in lab 1 do something in making solar cells?” What did Einstein
contribute?
(a)
(b)
(c)
(d)
He produced and measured the speed of radio waves.
He suggested that radiation in a black body was quantised.
He created the idea of a photon to explain black body radiation.
He discovered how to coat a metal surface with silicon to produce a voltage.
Question 11
“But how much energy will I need to run a 100W TV?” exclaimed Georgia. ”Mr. N said that the
wavelength of yellow light was 590 nm and I don’t know the work function of whatever metal they are
using in the solar cell but if we assume that all the energy of this light is converted into electrical energy,
then the number of photons we need every second is.. well, come on, Lucy, calculate it…
(N.B. Everyone doing this exam should perform the correct calculation as well – Mr. N.)
(a)
(b)
(c)
(d)
2.95 X 1020 photons
4.5 X 1023 photons.
9.82 X 1024 photons
5.6 X 1035 photons.
Question 12
“I just realised something!” yelled Jane. “A related concept to the work function is the
(a)
(b)
(c)
(d)
band gap”.
positive hole”.
conduction band.”
depolarisation layer.”
5- -
Question 13
Suddenly an argument broke out. “No, no, I didn’t call you a dope!” said Lucy. “I said, doping, you
know, when…
(a)
(b)
(c)
(d)
a small amount of another element replaces the atoms of another element in a crystal.”
a large amount of another element replaces the atoms of another element in a crystal.”
a small amount of another element contaminates another element in a crystal.”
a large amount of another element contaminates another element in a crystal.”
Question 14
But no one was listening. The confusion over dope and doping continued. Georgia ripped out an electrical
cable. Jane yelled “Wait! The liquid nitrogen in the cable will spill out and freeze us all to death! Not to
mention it will cut power to all of Mentie building.” The type of cable Jane was describing consists of
(a)
(b)
(c)
(d)
a superconducting core surrounded by a liquid nitrogen jacket.
a liquid nitrogen core surrounded by a conductive metal jacket.
a conductive metal core surrounded by a liquid nitrogen superconductor.
a liquid nitrogen core surrounded by a superconducting jacket.
Question 15
Georgia waved the cable like a snake. “I don’t care if we all freeze, I’m not a dope, dopant or even a
superconductor, for that matter” she exclaimed. As she said this, Mr. N. came into the room, dragging
behind him a really, really powerful electromagnet he had borrowed from some alien friends. He switched
it on and Georgia started levitating, letting go of the cable. Georgia was levitated due to
(a)
(b)
(c)
(d)
the Meissner effect.
Cooper pairs in her body moving through without resistance creating an opposing magnetic
field.
unpaired electrons in her body creating an opposing magnetic field.
an antigravity field created by the strong magnetic field.
6- -
Part B
Total marks (45)
Attempt Questions 16 – 24
Allow about 1 hour and 10 minutes for this part
Answer Questions 16 – 24 in this Booklet.
Show all relevant working in questions involving calculations.
Part B – Answer this section in the booklet provided.
Question 16 (7 marks)
Marks
The cable twisted away from Georgia. Mr. N. aimed the electromagnet at the 3
kg cable, switched on another button and the cable was instantly teleported to
Xenos, about 52 light years away. On this planet the cable has a weight of
24.5N
(a) Calculate the value of gravity on Xenos.
1
(b) On the return stroke of the teleportation, a birthday cake materialised.
However, the cake still had a lot of momentum from its journey. It
appeared in the air at a height of 2 metres at an angle of 30 to the horizontal
and landed 3 metres from its starting point, as shown below:
initial speed
trajectory of cake
height of ceiling 3 m
30
2m
3m
(i) Calculate the initial speed of the cake,
2
7- -
(ii) Calculate whether the cake would have hit the ceiling if the height of the
ceiling was 3 metres.
1
(iii) Describe qualitatively how the motion of the cake would have been
different on Xenos.
2
Question 17 (9 marks)
Marks
The cake landed at Jane’s feet, who was so stunned by the entire incident that
she failed to notice that the cake did not go ‘splat’ but rather went into an orbit
around her. A spoon that had followed the cake through the teleporter also
started orbiting Jane at a different radius.
(a) Identify a law that relates the periods of these two orbits.
1
(b) Describe the action of the cake and spoon if Jane were to
suddenly disappear, say, as if she was teleported accidentally.
1
8- -
(c) Jane suddenly found herself on Xenos, looking at some very
bemused aliens holding a snaking electrical cable. The Xenosians
were in the process of duplicating the way Earthlings measure the
metre.
Describe the way Earthlings measure the metre currently.
(d) Explain why Earthlings cannot check if the speed of light
changes.
9- -
2
2
(e) The Xenosians thought it was not a good idea for a student who
did not have the proper clearance from Earth channels to remain
on Xenos and so Jane was instantly transported back to the
Souberon room, just in time to catch the cake and spoon before
they fell to the ground.
Explain how a few minutes could have passed on Xenos while
only one second passed on Earth.
3
Question 18 (6 marks)
With all the moving about, Jane was feeling queasy, a similar feeling to what
astronauts experience during launch.
(a) Describe the forces that act on astronauts during launch.
10
- -
2
(b) Explain some methods used to help astronauts overcome these
forces.
2
(c) Outline how would Jane know that she is in a non-inertial frame
of reference in a launching rocket.
2
Question 19 (10 marks)
Mr. N. said “Sorry about that, but Georgia looked a bit dangerous; well, more dangerous than normal.” He
put the electromagnet down and locked it before Lucy had a chance to examine it. “Neat, isn’t it? It’s a
superconducting electromagnet using a high-temperature ceramic that has yet to be invented here on Earth.
It can reflect about 462 T and concentrate that field in a small volume to levitate almost anything.
(a) Explain why an external magnetic field cannot penetrate the
superconducting electromagnet.
11
- -
3
(b) Discuss the BCS theory, detailing why it does not apply to this
electromagnet.
5
(c) Explain why Georgia could hover above the electromagnet even
though she is not ferromagnetic.
2
12
- -
Question 20 (7 marks)
Lucy asked “But how does the electromagnet work?”
Mr. N. brought out a portable electron microscope about the size and shape of a hard disk and placed it on
the circuitry of the electromagnet. ”Here, let me show you” he said. After speaking some instructions to
the device, a hologram appeared displaying a silicon lattice with a few large atoms randomly placed in the
matrix.
Lei exclaimed “Oh, I see. There’s a p-doped layer in between two n-doped layers. It’s made of transistors!
But really smaller than the ones we have seen in class.”
(a) Describe how doping a semiconductor can change its electrical
properties to make a transistor.
2
(b) Assess the impact of the invention of transistors on society with
particular reference to their use in microchips and
microprocessors.
5
13
- -
Question 21 (6 marks)
Lucy was still holding her cake and spoon. “Are we going to have this cake or what!” she said.
Georgia had completely forgotten the events of the last few minutes and asked one of her “normally
tangential” questions: “But what would happen if I fired an ion beam at the superconducting
electromagnet? How could I figure out what ions are in the beam?”
(a) Outline Thomson’s experiment to measure the charge to mass
ratio of an electron, using equations where appropriate.
3
(b) Mr. N. demonstrated Thomson’s experiment using a proton
beam from the electromagnet (it also doubled as a portable
cyclotron). Another section of the electromagnet contained
antiproton beams. Of course, being fizzix students, what do you
do with a proton and anti-proton beam – you smash them
together to annihilate them! The collisions produced pairs of
gamma rays.
Calculate the frequency of the gamma rays from each protonantiproton collision.
14
- -
3
Part C
Total marks (10)
Attempt Question 22
Allow about 20 minutes for this part
Start this question on a new sheet of paper.
Show all relevant working in questions involving calculations.
22. The Rail Gun.
Jane asked Mr. N. “Why do you have a superconducting electromagnet in the first place? And when are we
going to eat this cake?”
“Well, this is a component from an experimental rail gun system to launch satellites into geosynchronous
orbit. The Xenosians loaned it to us but I thought we’d have a bit of fun with it before bringing it to the
rail gun project.” Mr. N. said.
(a) Describe how superconductors can be used in the development
of a maglev system for the rail gun.
2
(b) Describe qualitatively the differences between a low Earth and
geosynchronous orbit.
2
(c) Given that the mass of the earth is 5.98 X 1024 kg, calculate the
radius of a geosynchronous orbit.
2
(d) Explain why thermionic valves are not a good idea for satellites
launched by the rail gun.
3
(e) Discuss the importance of Newton’s Law of Universal
Gravitation in understanding and calculating the motion of
satellites.
3
End of Exam – Check your answers.
Epilogue
Everyone finally sang “Happy Birthday” to Jane and she cut the cake (with the spoon). Something didn’t
taste right about the cake (it had made a journey of 52 light-years, after all) and everyone politely excused
themselves from the party. Mr. N. brought the electromagnet back to the secret rail gun project. Georgia
spent the rest of the day repairing electrical cables. Lucy went back and solved that differential equation
for the motion of the rocket. Lei wrote another ancient history essay on Tiberius and nepotism. Jane had
an uneventful, but unexplosive, rest of her birthday.
15
- -
Kambala
Year 12 Half-Yearly Examinations 2005
Physics
Multiple Choice Answer Sheet
Name / Number: _________________________________
Select the alternative A, B, C or D that best answers the question. Fill in the response oval completely.
Sample
2+4=
(A) 2
(B) 6
(C) 8
(D) 9
A
B
C
D
If you think you have made a mistake, put a cross through the incorrect answer and fill in the new answer.
A
B
C
D
If you change your mind and have crossed out what you consider to be the correct answer, then indicate
this by writing the word correct and drawing an arrow as follows:
correct
A
B
C
D
1
A
B
C
D
2
A
B
C
D
3
A
B
C
D
4
A
B
C
D
5
A
B
C
D
6
A
B
C
D
7
A
B
C
D
8
A
B
C
D
9
A
B
C
D
10
A
B
C
D
11
A
B
C
D
12
A
B
C
D
13
A
B
C
D
14
A
B
C
D
15
A
B
C
D
16
- -
HSC Physics Half Yearly Exams 2005 Mapping Grid
Question
Mark
Content
Syllabus
Outcomes
Targeted
Performance Band
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16(a)
16(b)(i)
16(b)(ii)
16(b)(iii)
16(b)(iv)
17(a)
17(b)
17(c)
17(d)
17(e)
18(a)
18(b)
18(c)
19(a)
19(b)
19(c)
20(a)
20(b)
21(a)
21(b)
22(a)
22(b)
22(c)
22(d)
22(e)
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
2
1
1
2
2
3
2
2
2
3
5
2
2
5
3
3
2
2
2
3
3
9.2.1.1(2)
9.2.2.3(3)
9.2.2.7(2)
9.2.2.4(3)
9.2.2.6(2)
9.2.2.8(2)
9.2.4.4(2)
9.4.1.6(2)
9.4.1.3(3)
9.4.2.5(2)
9.4.2.4(3)
9.4.3.3(2)
9.4.3.4(2)
9.4.4.5(2)
9.4.4.4(3)
9.2.1.2(3)
9.2.2.3(3)
9.2.2.3(3)
9.2.2.3(3)
9.2.2.3(3)
9.2.2.5(3)
9.2.2.10(2)
9.2.4.4(2)
9.2.4.5(2)
9.2.4.6(2)
9.2.2.4(2)
9.2.2.5(2)
9.2.4.1(2)
9.4.4.4(3)
9.4.4.5(2)
9.4.4.4(3)
9.4.3.5(2)
9.4.3.4(3)
9.4.2.6(2)
9.4.3.4(3)
9.4.4.5(3)
9.2.2.4(2)
9.2.2.10(2)
9.4.3.8(2)
9.2.3.5(2)
H6
H1
H4
H4
H3
H4
H1,H3
H3
H4
H1
H10
H2
H4
H4
H2
H6
H6
H6
H6
H6
H1
H6
H3
H2
H7
H3
H3
H9
H2
H2
H2
H3
H4
H2
H5
H4
H7
H3
H4
H2
2
2
3
5
2
2
4
2
5
2
5
4
2
3
4
4
5
4
5
4
2
4
3
3
4
3
2
4
3
2-6
4-6
3
2-6
3
4-6
3
2
5
4
4
1- -
Correct
Answer
Question 16 (3 marks)
Marks
During your course you have gathered and analysed information on the contribution of one scientist to the
development of space exploration.
Explain how this scientist’s ideas contributed to our understanding of space science.
(b)
MARKING GUIDELINES
Criteria

Relates how the ideas of the scientist had the effect of increasing our
understanding of space science.

Describes some findings of the scientist.
3
Marks
3
1-2
Sample answer:
Goddard is considered the “father of space flight”. He performed many experiments in the 1920’s and 30’s on rocketry and was
the first to develop a liquid fuel-based rocket. This allowed for higher altitudes and ranges for rockets that eventually led to
rockets capable of reaching space.
Question 17 (7 marks)
Marks
A 100 kg satellite is in orbit at an altitude of 38400 km above the surface of the Earth. If the radius of the
Earth is 6380 km and the mass of the Earth is 6.2 X 1021 kg,
(a)
State the specific name of this orbit.
1
MARKING GUIDELINES
Criteria

Correct answer.
Marks
1
Sample answer:
Geostationary orbit.
(b)
Calculate the value of gravity at this altitude.
2
MARKING GUIDELINES
Criteria

Obtains correct result.

Correctly applies equations to solve the problem.
Marks
2
1
Sample answer:
F
(c)
Gm1m2 6.67 X 10 11 X 100 X 6.2 X 10 21
F .0206

 0.0206  g  
 2.06 X 10 4 ms 2
2
2
m 100
d
(38400000  6380000)
Calculate the orbital velocity of the satellite relative to the surface of the
Earth.
MARKING GUIDELINES
Criteria

Obtains correct result.

Correctly applies equations to solve the problem.
Marks
2
1
Sample answer:
F
2
mv 2
 mg  v  gr  2.06 X 10 4 X (38400000  6380000)  9230m / s
r
2- -
(d)
Discuss the stability of this orbit.
2
MARKING GUIDELINES
Criteria
Marks

Explains how the orbit is affected by atmospheric drag, gravitational
perturbations, electromagnetic interactions.
2

States some points about geostationary orbits.
1
Sample answer:
A geostationary orbit parks a satellite above the same position of the earth. Being far above the atmosphere, it is not subjected to
atmospheric drag. As seen in part (c), there is still a weight force acting on the satellite and the influence of other bodies, eg the
Moon and the Sun, may have a slight affect on the stability of the orbit.
Question 18 (3 marks)
Marks
Outline the features of the aether model for the transmission of light.
MARKING GUIDELINES
Criteria

Gives an in-depth description of the main characteristics of the aether
model.

Describes two points of the aether model.
3
Marks
2-3
1
Sample answer:
The aether model for the transmission of light assumes that there is a medium called aether that is responsible for transmitting
light. This medium is required because at the time that the aether model was proposed, all waves required a medium. Scientists
of the time knew that space was effectively a vacuum therefore another medium was required for starlight to reach the earth.
The properties of this aether medium allowed light to pass through it.
Question 19 (4 marks)
Marks
Discuss the role of the Michelson-Morley experiments in science in making
determinations about competing theories.
MARKING GUIDELINES
Criteria
4
Marks

Explains how the Michelson-Morley experiment changed the theories of
light that led to the current ideas about the nature of light.
4

Gives a brief historical account of the development of the particle and
wave models of light.
3

Accounts for the results of the Michelson-Morley experiment and states
how it changed the way scientists viewed the nature of light.
2

Provides a brief description of the Michelson-Morley experiment.
1
Sample answer:
The Michelson-Morley experiment was set up to determine the speed of the earth through a light-transmitting medium called the
aether. The experiment was designed to test the prevailing idea of the time that light must travel through such an aether. This
idea had its roots in earlier experiments.
People had long debated whether light is a particle or a wave. In a definitive experiment done by Young in 1803, light was
shown to be a wave when it was passed through a double slit, causing an interference pattern. Thus since light was a wave it
required a medium – this was called the aether. The Michelson-Morley experiment attempted to establish the speed of the earth
through this aether in space. The results turned the ideas of the day on their head as a null result was obtained after many
measurements. This forced scientists to either question the methodology of the experiment or the accepted theory of light. Once
the methodology of the experiment was accepted, then the theory of light was replaced. This led to our current understanding of
light as both a particle and a wave – a photon.
3- -
Question 20 (6 marks)
Marks
Discuss the relationship between theory and the evidence supporting it, using
Einstein’s predictions based on relativity that were made many years before
evidence was available to support it.
MARKING GUIDELINES
Criteria
6
Marks

Provides further points and generalisations about the nature of scientific
research and the use of the scientific method.
5-6

Explains the predictive power of a good theory such as relativity and
how it can provide experiments that can be used to test it.
3-4

States some of the predictions of relativity theory.
1-2
Sample answer:
All theories proposed by scientists require some form of experimentation to strengthen or disprove the theory. The theory of
general relativity was proposed at a time when many of its predictions could not be tested. The general theory of relativity
related the strength of a gravitational field to its ability to warp space-time. In 1916 was the general theory of relativity was
published this could not be tested. However, in 1919 there was a total eclipse of the Sun that allowed scientists to look at stars
close to, and according to general relativity, directly behind the Sun. This is because the Moon blocks out most the sunlight
except for the coronal discharge during an eclipse. According to general relativity, stars directly behind the sun should be visible
at the edge of the Sun because the gravity
Question 21 (10 marks)
Marks
During the course you have planned, chose equipment or resources for, and performed a firsthand investigation to demonstrate the production of an alternating current.
(a) Describe briefly your investigation.
2
MARKING GUIDELINES
Criteria

States some of the equipment used and rationalises their use.

Provides a correct method for the production of an alternating current.
Marks
2
1
Sample answer:
An alternating current can be produced by turning an AC generator at high speed. The higher the kinetic energy given
to the armature, the higher the current. The AC generator consists of an armature with many turns of coil immersed in
a strong magnetic field generated by a permanent magnet. As the armature is turned in the magnetic field, an induced
emf is created that is sinusoidal in nature.
(b) Explain the differences between this AC generator and DC
generators.
MARKING GUIDELINES
Criteria

Relates the differences between AC and DC generators to their effect on
a generated current.
Sample answer:
An AC generator creates a sinusoidal current that becomes positive and negative at the same
frequency as the rate of turn of the armature. A DC generator creates a current that builds up to
a value and drops to zero at twice the rate of the armature spin rate.
4- -
2
Marks
1-2
(c) Discuss the advantages and disadvantages of AC and DC generators and
relate these to their use. In your discussion, you should address the
competition between Westinghouse and Edison to supply electricity to cities.
MARKING GUIDELINES
Criteria
6
Marks

Provides a historical context of the use of AC and DC generators using
the competition between Westinghouse and Edison as examples.
5-6

Compares the advantages and disadvantages of AC and DC generators.
3-4

States some features of AC and DC generators.
1-2
Sample answer:
AC and DC generators have some similiarities and many differences. DC generators can produce constant low voltages at high
currents generally while AC generators produce a sinusoidally changing voltage. While a DC power output is constant, AC
power output varies according to the frequency of the cycle. AC voltages can be transmitted over longer distances than DC,
which require repeater stations. In the 1880s Edison set up a DC power grid in Chicago while Westinghouse set up an AC grid
in the same city. Edison had to place his power stations within the city every few blocks whereas Westinghouse placed his
power stations outside the city and transmitted the power into the city. Much disinformation about the safety of AC and DC was
spread by Edison and Westinghouse in their competition to supply electricity. Eventually Westinghouse’s AC network won over
Edison’s DC network. This was mainly due to economic reasons – few power stations to set up, more efficient transmission of
power and hence less electrical energy loss, etc.
Question 22 (3 marks)
Marks
Explain how induction is used in cooktops in electric ranges.
MARKING GUIDELINES
Criteria

Relates the application of Lenz’s law to its use in induction cooking.

States some features of induction cooking.
3
Marks
2-3
1
Sample answer:
Induction cooking involves placing a solenoid under a non-conductive surface such as glass. A high AC current is run through
the solenoid causing an intense changing magnetic field in the volume above the non-conductive surface. A metal pot placed on
the glass will be immersed in the changing magnetic field. According to Faraday’s law, an emf will be induced in the metal pot.
Since the metal has a resistance, an induced current will result. Lenz’s law states that the induced current will be formed in such
a way as to oppose its production. This means that the electrical energy created by the magnetic induction will be attempted to
be destroyed by the induced current, causing the electrical energy to transform into heat. It is this heat that is used for cooking.
Question 23 (4 marks)
Marks
Discuss how difficulties of heating caused by eddy currents in transformers
may be overcome.
MARKING GUIDELINES
Criteria

Provides points in terms of energy changes / transformations

Describes some methods for reducing eddy currents or reducing heating
effects.

States how eddy currents are produced in transformers.
4
Marks
4
2-3
1
Sample answer:
Eddy currents are produced as a result of Lenz’s law. When a changing magnetic field induces an emf in a conductor according
to Faraday’s law, the resulting emf causes a current in any material that has resistance. These induced currents are referred to as
eddy currents because they go against the main current that is causing the changing magnetic field. By reducing the size of the
eddy currents, the transformation of electrical to magnetic energy is made more efficient and loss of energy due to heat is
minimised. This can be done by lamination, which is splitting a single large conductor into many smaller plates. This does not
allow a large induced current to build hence minimising energy loss to heat. Other methods of reducing these heat losses include
5- -
running the transformer at higher voltages, hence producing lower currents and selecting the type of material with a reasonable
resistance to reduce the current.
Question 24 (5 marks)
Marks
Discuss the impact of the development of transformers on society.
MARKING GUIDELINES
Criteria
5
Marks

Gives a historical account of the use of transformers and outlines how
transformers have changed society.
4-5

Describes how transformers have allowed various technologies to
develop.
2-3

States some of the uses of transformers.
1
Sample answer:
Transformers have transformed our society (sorry I couldn’t help the pun!). Since transformers can change one value of voltage
to another, they find uses in all type of AC devices. Electrical power is supplied to homes at a voltage of 240V AC. Many
devices such as computers, phones, etc. operate at far lower voltages, typically 5-12V. A transformer is used to step down the
240V supply voltage to required voltage for the device. Other devices require high voltages up to 50,000 V such as TV,
computer monitors and microwave ovens. In this case a step up transformer is used.
The use of these transformers has allowed the development of many technologies based on electrical energy, to the extent that
electrical energy dominates our energy usage today. At the turn of the twentieth century, the primary energy sources in the
home were coal, wood and gas. These have been phased out by electrical energy predominantly. The use of transformers in
electrical devices allowed a single voltage to be supplied to homes and industry that was changed on-site, making electrical
energy very convenient and easy to use. This has allowed many industries based on electronics to flourish in the twentieth
century such as microproccesors, consumer electronics, computer programming, etc. This has resulted in millions of jobs being
created. People in the twenty-first century would find it difficult not to use electrical devices, most of which employ a
transformer, hence transformers are part of our everyday lives.
6- -
Question 25 (20 marks)
Marks
(a) Outline Newton’s analysis of escape velocity.
3
MARKING GUIDELINES
Criteria
Marks
3

Has a complete description of Newton’s analysis of escape velocity.

Gives a brief description of Newton’s analysis of escape velocity.
2

Defines / Uses the concept of escape velocity.
1
Sample answer:
(b) Derive an expression for escape velocity in terms of the centripetal and
gravitational forces acting on a projectile.
MARKING GUIDELINES
Criteria

Correctly rearranges and derives an expression for velocity.

States the centripetal and gravitational forces acting on a projectile.
2
Marks
2
1
Sample answer:
mv 2
mv 2
Gm1m2
 Fg  mg
 mg 
r
r
r2
v2
Gm
 gv  rg 
r
r
Fc 
(c) Explain how Tsiolkovsky’s tower could launch a projectile into a stable
orbit.

MARKING GUIDELINES
Criteria
2
Marks

Relates the causes of projectile motion to its effect of setting a satellite
into orbit.
2

Briefly states some features of Tsiolkovsky’s tower.
1
Sample answer:
(d) Discuss some factors that affect the strength of the gravitational force at
the bottom and top of the tower.
MARKING GUIDELINES
Criteria

3
Marks
Provides points for difference in gravitational acceleration between the
top and bottom of the tower in terms of distance from the centre of the
earth.
3

Differentiates between the value of gravity at the top and bottom of the
tower.
2

States some factors that affect gravitational field.
1
Sample answer:
7- -
(e) Describe an experiment that could be performed to measure the value
of the acceleration due to gravity at the top of the tower.
MARKING GUIDELINES
Criteria
3
Marks
3

Provides points as to how the experiment is reliable and valid.

Identifies variables and control in the experiment.
2

States an experimental method that is correct.
1
Sample answer:
(f) Contrast qualitatively the value of gravitational acceleration obtained at
the top and bottom of the tower.
MARKING GUIDELINES
Criteria

Provides reasons for why the value of gravity at the top is lower.

States that the value of gravity at the top of the tower is lower than at the
bottom of the tower (surface of the earth)
2
Marks
2
1
Sample answer:
(g) Calculate the work done in moving a 100 kg satellite up a 300 km
tower.
MARKING GUIDELINES
Criteria

Obtains correct answer.
Sample answer:
Assuming g to be constant at 9.8 m/s2,
Marks
1
W  F.d  mgd 100X9.8X300,000  28400000J
(h) Discuss the effect of the Earth’s orbital and rotational motions on a
satellite launched from the top of this tower.

MARKING GUIDELINES
Criteria

1
4
Marks
Provides points for the motion of the satellite as a relative velocity to the
earth and how this relative velocity is affected by the earth’s orbital and
rotational motions.
4

Relates the motion of the satellite to the orbital and rotational motion of
the earth.
2-3

States some effects of the Earth’s orbital and rotational motions on a
satellite.
Sample answer:
8- -
1
Question 26 – Motors and Generators (20 marks)
Marks
The national electricity grid requires many components: electrical power stations, transformers, cabling
from cross-country to home, sub-stations and other components as well. This grid has been developed over
the last 130 years.
(a) Outline the discovery of the generation of an electric current by a
moving magnet by Michael Faraday.
MARKING GUIDELINES
Criteria

Give a chronological or logical order to the discoveries made by Faraday

Provides some points about the discovery of electrical generation by
Faraday.
3
Marks
3
1-2
Sample answer:
(b) Derive/Define and explain an expression for the generation of emf in
terms of the change in magnetic flux in an electrical generator.
MARKING GUIDELINES
Criteria

Relates Faraday’s law to how it generates electricity.

States Faraday’s law either in language or mathematically.
2
Marks
2
1
Sample answer:
(c) Explain the role of the transformers in electricity sub-stations.
MARKING GUIDELINES
Criteria

Relates the reasons for the use of transformers in sub-stations (causes) to
the production of electricity (effects)
2
Marks
1-2
Sample answer:
(d) Discuss why some electrical appliances used in the home that are
connected to the mains domestic power supply use a transformer.
MARKING GUIDELINES
Criteria
3
Marks

Provides points about how transformers allow AC voltages to be
converted.
3

Provides points about the need for different appliances to run on
different voltages.
2

Defines/Uses the definition of transformer and mains domestic power
supply.
1
Sample answer:
9- -
(e) Describe an experiment to demonstrate the production of an alternating
current.
MARKING GUIDELINES
Criteria

Identifies some variables and controls in the experiment.

States an experiment that can produce A.C.
3
Marks
3
1-2
Sample answer:
(f) Contrast the use of step-up and step-down transformers in the national
electricity grid.
MARKING GUIDELINES
Criteria
2
Marks

Explains the difference between the uses of step-up and step-down
transformers and their applications in the national grid.
2

Defines/Uses the definition of step-up and step-down transformers.
1
Sample answer:
(g) Calculate the secondary voltage produced when a transformer with a
winding ratio of 33:1 has an input voltage of 330kV
MARKING GUIDELINES
Criteria

Provides correct answer.
1
Marks
1
Sample answer:
n p Vp
n
1
 Vs  V p . s  330000X
 10kV
n s Vs
np
33
(h) Discuss the energy losses that occur as energy is fed through
transmission lines from the generator to the consumer.

MARKING GUIDELINES
Criteria
4
Marks

For each stage in the transmission of electricity, provides points for how
energy is lost and in what forms.
3-4

Briefly provides points for the transmission of electricity from generator
to consumer.
1-2
Sample answer:
10
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