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12PHYSICS FIELDS Solutions
VICTORIAN CERTIFICATE OF EDUCATION
2017
NAME:_________________________
TEACHER: ________________________
PHYSICS
School Assessed Coursework: Test
Fields - Solutions
Reading Time: 10 minutes
Writing time: 60 minutes
QUESTION AND ANSWER BOOK


Section
Number of
questions
Number of questions
to be answered
Number of marks
A
6
6
39
Students are permitted to bring into the examination room: pens, pencils, highlighters,
erasers, sharpeners, rulers, up to two pages (one A4 sheet) of pre-written notes (typed
or handwritten) and one scientific calculator.
Students are NOT permitted to bring into the examination room: blank sheets of paper
and/or white out liquid/tape.
Materials Supplied
 Question and Answer book of 11 pages. A formula sheet.
Instructions
 Write your student name and teacher name in the space provided above on this
page.
 Unless otherwise indicated, the diagrams in this book are not drawn to scale.
 All written responses must be in English.
At the end of the examination
 Close your Question and Answer booklet and ensure your name and your teacher’s
name is clearly printed on the front cover.
Students are NOT permitted to bring mobile phones and/or any other unauthorised
electronic devices into the examination room.
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12PHYSICS FIELDS Solutions
Area of study – Fields
Instructions
Answer all questions in the spaces provided. Use black or blue pen.
Where an answer box has a unit printed in it, give your answer in that unit.
You should take the value of g to be 9.8 m s-2.
Where answer boxes have been provided, write your final answer in the box.
In questions where more than one mark is available, appropriate working should be shown.
Unless otherwise indicated, diagrams are not drawn to scale.
Question 1 (6 marks)
In 1820, Hans Christian Oerstead discovered that a current carrying wire would produce a magnetic field.
a.
Draw 3 magnetic field lines around the current carrying wire.
1 mark
In 1824, William Sturgeon invented an electromagnet by coiling a current carrying wire around
a piece of soft iron.
b.
Draw 5 magnetic field line around the electromagnet.
1 mark
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12PHYSICS FIELDS Solutions
At point P the magnetic field provided by the solenoid is twice the strength of that of the Earth. The
strength of the magnetic field of the Earth is 50 μT.
N
P
c.
Calculate the magnitude and direction of the resultant magnetic field at point P. On the
diagram, illustrate the resultant magnetic field at P with an arrow.
3 marks
________________________________________________________________________________
 50 
B  50  100

  tan 

________________________________________________________________________________
2
2
1
 100 
 B  112 T
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  26.6
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N 63.4W
________________________________________________________________________________
________________________________________________________________________________
Magnitude
 B  112 T
Direction
N 63.4W
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12PHYSICS FIELDS Solutions
Question 2 (7 marks)
Consider the two charged plates that are separated by small distance of 2.3 cm. The potential difference
across the battery is 9.0 V
2.3 cm
9V
a.
Draw 4 electric field lines between the two plates.
1 mark
b.
Calculate the magnitude of the electric field between the plates.
1 mark
V
________________________________________________________________________________
E
d
9
________________________________________________________________________________
E
0.023
________________________________________________________________________________
E  391
E  391
N C-1
An electron is accelerated from rest from one plate to the other.
c.
Calculate the magnitude of the change in electrons kinetic energy as it traverses between
the plates.
2 marks
________________________________________________________________________________
W  qV
________________________________________________________________________________
19
W  1.6 10  9.0
W  1.44 1018
________________________________________________________________________________
________________________________________________________________________________
W  1.44 1018
J
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12PHYSICS FIELDS Solutions
Kes says that the force on the electron is constant as it moves between the plates but her friend
Nelix argues that force on the on electron increases as it accelerates.
d.
Who is correct, Kes or Nelix? Explain your response.
3 marks
________________________________________________________________________________
 Kes is correct.
________________________________________________________________________________
 The electric field between the plates is uniform.
 The F = qE, since q and E are constant, the force on the proton is
________________________________________________________________________________
also constant.
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
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12PHYSICS FIELDS Solutions
Question 3 (5 marks)
A proton of mass 1.67 × 10-27 kg moving at 2.5 × 106 m s-1. The proton moves into a magnetic field and
experiences a force of 2.0 × 10-14 N.
2.5 × 106 m s-1
a.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Which direction is the force on the proton as it enters the magnetic field?
1 mark
_________________________________________________________________________
 Down
b.
Calculate the magnitude of the magnetic field.
2 marks
F  qvB
________________________________________________________________________________
2.0 1014  1.6 1019  2.5 106  B
 B  5.0 104
________________________________________________________________________________
________________________________________________________________________________
50 mT
c.
Calculate the radius of the protons path in the magnetic field.
2 marks
________________________________________________________________________________
mv 2
________________________________________________________________________________
r
F
  2.5 10

27
6 2

14
________________________________________________________________________________
2.0 10

1.67 10
r
r  0.52
________________________________________________________________________________
52 cm
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12PHYSICS FIELDS Solutions
Question 4 (9 marks)
The gravitational field at the International Space Station (ISS) is 8.7 N kg-1.
Earth
a.
Calculate the altitude of the ISS
3 marks
_________________________________________________________________________
GM
Altitude  r  rEarth
g 2
r
________________________________________________________________________________
6.67 1011  6.0 1024
Altitude  6.78 106  6.37 106
8.7 
r2
________________________________________________________________________________
Altitude  412300
 r  6.78 106
________________________________________________________________________________
________________________________________________________________________________
412 km
b.
Calculate the speed of the ISS.
3 marks
________________________________________________________________________________
v2
r
________________________________________________________________________________
g
2
v
________________________________________________________________________________
8.7 
6.78 106
________________________________________________________________________________
v  7682
________________________________________________________________________________
7680 m s-1
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12PHYSICS FIELDS Solutions
c.
Calculate the period of ISS’s orbit.
3 marks
________________________________________________________________________________
2
4 r
T2
________________________________________________________________________________
g
4 2  6.78 106
T2
________________________________________________________________________________
8.7 
________________________________________________________________________________
T  5548 s
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
1.52 hours
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12PHYSICS FIELDS Solutions
Question 5 (6 marks)
In the book The Martian, written by Andy Weir, the protagonist, Mark Watney (m = 55 kg), has been
stranded on the surface of Mars and must use a rocket, of mass 800 kg, to project himself into space in
order to be rescued by a crew in orbiting Mars. Mars has a radius of 3.4 x 106 m and he must get to a
height above the surface of 3.6 x 106 m in order to be rescued.
A1
a.
A2
A3
A4
Calculate the amount of energy required to lift Watney and his rocket from the Mars’
surface to an altitude of 3.6 x 106 m.
3 marks.
________________________________________________________________________________
1
1
1
A2   a  b  h
A3   a  b  h
a  b h
2
2
2
________________________________________________________________________________
1
1
1
A1   3.4  2.7    0.6  106 
A2  1.7  2.7   1106 
A3  1.7  1.2   1 106 
2
2
2
A1 
________________________________________________________________________________
6
6
6
A1  1.83  10
A2  2.20  10
A3  1.45  10
________________________________________________________________________________
1
a  b h
AT  A1  A2  A3  A4
2
________________________________________________________________________________
AT  6.63 106 J/kg
1
A4   0.9  1.2   1106 
2
________________________________________________________________________________
A4 
A4  1.05  106
5.58 × 109 J
E  mAT
E  855  6.63 106
E  5.58  109 J
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12PHYSICS FIELDS Solutions
The NASA team informs Watney that the rocket can do 4.5 x 109 J of work, and he must strip the rocket
of any unnecessary mass to ensure he makes the required height.
b.
How much rocket mass must Watney leave behind to be sure he makes the required
height above Mars’ surface?
3 marks.
________________________________________________________________________________
E  mAT
mL  855  679
4.5  109  m  6.63  106
________________________________________________________________________________
 mL  176 kg
 m  679 kg
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
176 kg
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12PHYSICS FIELDS Solutions
Question 6 (6 marks)
In 1821, Michael Faraday created the first electric motor. It consisted of a wire that hung in a liquid
mercury which rotated around a permanent magnet. In 1838, Moritz Von Jacobi created an electric motor
that drove a boat with 14 people across a river.
The diagram shows a DC motor.
B
A
a.
C
D
From the point of view shown in the diagram, does the coil rotate clockwise or anticlockwise? Explain.
3 marks
________________________________________________________________________________
 Anticlockwise
________________________________________________________________________________
 The current flows around the coil D, C, B, A and the magnetic
field is to the left.
________________________________________________________________________________
 Using RH rule, the force on CD is up and the force and AB is
down.
________________________________________________________________________________
________________________________________________________________________________
b. Explain how the split ring commutator keeps the motor rotating in one direction.
3 marks
________________________________________________________________________________
 The split ring commutator changes the direction of the current in
________________________________________________________________________________
the coil every half turn.
 The forces on the side AB and DC change direction every half
________________________________________________________________________________
turn.
 The torque on the coil remains in the same direction.
________________________________________________________________________________
________________________________________________________________________________
END OF OUTCOME 1