Download Chapter 1 - Medical applications of physics

Chapter 1 - Medical applications of physics
1
Link each type of wave with its uses and properties
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2
The diagram shows the oscilloscope trace for an ultrasound A-scan for part
of a person’s thigh. The trace is used to measure the thickness of the
person’s fat and muscle.
Each square on the screen represents a time of 10 millionths of a second
(0.000 010 s).
a
How much time does it take for the ultrasound pulse to travel to the
patient’s bone and back? The speed of ultrasound through tissue is
1540 m/s.
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b
Calculate the thickness of the layer of fat. The speed of ultrasound in the
fat = 1540 m/s. Give your answer in millimetres.
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c
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Why do the reflections from the different layers of muscle get weaker
with depth?
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(1)
The diagram shows a converging lens.
a
Complete the ray diagram to show the position of the image.
b
Describe the image that is formed.
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c
Calculate the magnification produced by this lens.
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d
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Where would a lens be used in this way? Give a reason for your answer.
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The following diagram shows a diverging lens.
e
Calculate the power of the lens. Show your working clearly and give the
unit.
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f
(3)
Complete the ray diagram to show the position of the image.
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g
Describe the image that is formed.
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(3)
The diagram shows a ray of light travelling through a semicircular glass block
at various angles of incidence, A, B and C.
a
Which of the angles A, B, C or D represents the critical angle?
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b
What is happening in Figure C?
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c
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(1)
If angle A is 30° and angle D is 54°, calculate the refractive index of the
glass.
Write down the equation you use. Show clearly how you work out your
answer.
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d
Calculate the critical angle.
Show clearly how you work out your answer.
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Chapter 2 - Using physics to make things work
1
A boy is making a mobile of birds in flight. The diagram shows a thin sheet of
card that he has cut in the shape of a bird. There are holes in the card at A
and B. He decides to find the centre of mass of the shape.
a
What is meant by the centre of mass of an object?
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b
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In this question you will be assessed on using good English, organising
information clearly and using specialist terms where appropriate.
Describe how you would find the centre of mass of the mobile shape.
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c
The wrestler is shown in a ‘ready’ stance.
Which two features of this stance make the wrestler very stable?
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d
A waiter trips while carrying a tray of mugs and the tray starts to tilt.
The white dots indicate the position of the centre of mass of each mug.
i
Which mug will have started to topple over already?
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ii
(1)
Which mug will topple over next if the tray is tilted even more?
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iii Which mug would be the last to topple?
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2
The diagram shows a brake lever on a bicycle.
The lever is pulled with a force of 50 N and then stops turning.
a
Calculate the moment of the force about the pivot.
Write down the equation you use. Show clearly how you work out your
answer and give the unit.
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b
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Explain why the brakes are more effective if the lever is pulled at the
end as shown.
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c
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There is a clockwise and an anticlockwise moment about the pivot. What
can be said about these moments if the lever is not moving?
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d
(1)
Calculate X, the force the cable exerts on the lever.
Show clearly how you work out your answer and give the unit.
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3
The ‘pirate ship’ is a very common amusement park ride. The ride is simply a
giant pendulum.
The designers of the ride wanted there to be three seconds between the
highest points on each side of the ride.
a
What would the time period of this ride be?
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b
(1)
Calculate the frequency of the ride.
Write down the equation you use. Show clearly how you work out your
answer and give the unit.
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c
(2)
When the ride was sold to another amusement park, the dimensions of
the ride were reduced. As a result of this, the distance between the
pivot and the centre of mass of the ship was reduced. How would this
affect the time period?
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The ship swings through an angle of 65° to the vertical on each side. While it
does so, it is moving in a circular path.
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d
Describe the direction of the centripetal force acting on the ship when it is
moving.
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e
What provides the centripetal force in this case?
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f
(1)
(1)
The new operators of the ride use the drive motors to increase the
maximum speed of the ship to its original value as it travels past its
lowest point. Explain why they should have the ride carefully checked
before they do so.
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Using magnetic fields to keep things moving
1
A magnet is held suspended near a wire that has a magnetic field around it.
a
What causes the magnetic field to be produced around a wire?
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b
(1)
When released, the magnet rotates slowly in the direction shown. What
is the name for this effect?
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c
(1)
Give two ways in which the force on the magnet could be reversed.
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d
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Give two ways of increasing the force on the magnet.
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The wire and the magnet are now arranged as shown below. A current passes
through the wire and the wire experiences a force. Only part of the
magnetic field from the magnet is shown.
e
Use Fleming’s left-hand rule to find the direction of the force on the
wire. Explain fully how you used the rule.
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2
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The diagram shows a wire being moved upwards through the magnetic field
between two poles of a magnet. A voltmeter is connected across the wire.
a
Explain why the voltmeter gives a reading when the wire is being moved
upwards but not when it is stationary.
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b
How does the potential difference change if the wire is moved
i
downwards
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ii
sideways?
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3
a
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(1)
Complete the diagram to show the basic structure of a transformer.
Label each part.
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b
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Explain the difference between a step-up transformer and a step-down
transformer.
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c
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What must be happening in the iron core of the transformer when it is
producing a potential difference on the output?
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d
The following equation can be used when designing transformers.
Vp
Vs
i

np
ns
Give the meaning of each of the symbols in the equation.
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ii
(4)
Calculate Vp if Vs = 55 V, np= 320 and ns = 40
Write down the equation you use. Show clearly how you work out your
answer.
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iii Calculate ns if Vp = 11 000 V, Vs = 230 V and np = 55 000
Write down the equation you use. Show clearly how you work out your
answer.
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iv
Calculate the output current from this transformer when the input
current is 2.5 A.
Show clearly how you work out your answer and give the unit.
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e
Give a typical frequency at which a switch mode transformer works.
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f
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(1)
Give two advantages of a switch mode transformer compared with an
iron-core transformer.
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