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1.
One type of particle detector at CERN consists of a thin wafer of silicon. On both sides of the
wafer are aluminium electrodes, with a voltage of 100 V across them. The electrodes are 300
m apart. When a particle enters the wafer, it creates an electron/hole pair as shown (a hole acts
like a positive electron).
+100 V
Particle
Electrode
300 m
Hole
Electron
Electrode
0V
Electric field = ....................................
(2)
Calculate the force due to this field on an electron in the wafer.
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Force = ..................................
(2)
Indicate on the diagram the direction of this force on the free electron shown. Explain why the
force has this direction.
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(2)
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1
The hole can move in the direction of the electric field, provided that it can gain enough energy
from the field to move it from one atom to the next. The distance between atoms is
2.8 × 10–10 m. Calculate how much energy the hole gains in moving this distance in the
direction of the field.
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Energy = ...................................
(2)
(Total 8 marks)
2.
A student has four identical lamps. She connects up circuit 1. Using 5 V the lamp flashes briefly
when the switch is moved from left to right. She then connects up circuit 2. Using
10 V with this arrangement, each of the four lamps gives a similar flash to the lamp in circuit 1.
5V
C
10 V
Circuit 1
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10 V
C
10 V
Circuit 2
2
Discuss the physics of what the student has observed.
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(6)
(Total 6 marks)
The Westlands School
3
3.
In 1998 NASA launched the probe called Deep Space 1. Once in orbit, this probe was the first
to use a solar powered ion drive to propel it on its mission.
The diagram shows the main features of the ion drive.
Ion
source
Accelerator
+
+
+
+
+
+
+
Positive
electrode
+ 1060 V
+
+
+
+
+
+
+
+
+
Negative
electrode
– 225 V
Atoms of xenon are ionised and then accelerated until they are ejected out of the rear of the
probe, providing the means of propulsion.
Explain how the ions are accelerated.
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(2)
The Westlands School
4
A xenon atom is ionised by the loss of a single electron. Show that its speed after being
accelerated is about 4 × 104 m s–1.
Mass of xenon ion = 2.20 × 10–25 kg.
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(4)
The mass of xenon ejected in one second is 2.10 × 10–6 kg. Calculate the thrust on the space
probe.
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Thrust = ....................................................................
(3)
Simply firing xenon ions into space would leave the probe negatively charged. Suggest a reason
why this would lead to reduced thrust.
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(1)
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5
Chemical rockets eject their propellant at about a tenth of the velocity achieved by ion drives,
but produce much greater thrust by ejecting more than a thousand kilograms per second.
Suggest why ion drives may be preferable for missions extending over long distances and
periods of time.
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(2)
(Total 12 marks)
The Westlands School
6
4.
It has been suggested that the centripetal force causing the Moon to orbit the Earth might be the
result of electrical attraction and not gravitational attraction at all. Assuming the necessary force
could arise as a result of the Earth and the Moon carrying equal charges (of opposite sign), show
that the magnitude of these charges would have to be about 6 × 1013C.
Data:
Mass of Moon
Radius of Moon’s orbit
Time of Moon’s orbit
= 7.4 × 1022 kg
= 3.8 × 108 m
= 27 days
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(Total 6 marks)
5.
State Faraday’s law of electromagnetic induction.
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(2)
The Westlands School
7
Microphones convert longitudinal sound waves into electrical signals, which can be amplified.
One type of microphone consists of a flexible diaphragm connected to a coil of wire, which is
near a cylindrical magnet.
Rigid
frame
Flexible
diaphragm
N
Coil
Cylindrical
magnet
S
N
To amplifier
Describe how sound waves are converted into electrical signals. You may be awarded a mark
for the clarity of your answer.
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(4)
(Total 6 marks)
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