Transcript Presentation - science

P3 Exam questions
• The following questions are examples of
questions taken fro previous exams.
• If you can answer these and can learn these
answers and apply them to similar questions
you will do really well in the exam.
1. What is Ultrasound?
• Ultrasound is a sound that has a frequency
above the human limit of hearing
• i.e. a sound with a frequency above 20 000
Hz (20 kHz)
2. Distance from reflected sound
•
•
•
•
Distance = speed x time
Time to wall and back = 0.06 seconds,
so time just to wall = 0.06/2 = 0.03 s
Distance = 340 x 0.03 = 10.2 m
3. Uses of ultrasound
• Describe a non-medical use for ultrasound
• Ultrasound can be used to clean delicate
objects.
• The object is placed in a liquid and then
bombarded with ultrasound that gently
cleans it
4. State an ultrasound treatment
• Ultrasound can be used to break down
kidney stones
5. What is an X-Ray and how big are
the wavelengths?
• An X-ray is part of the EM spectrum
• that has a wavelength about the size of the
diameter of an atom
6. Define Time period and frequency
• How does the time period of a pendulum vary
with its length?
• As the length increases the time period
increases
• A pendulum has a period of 0.5 seconds, what is
the frequency?
• f = 1/T
• f = 1/0.5 = 2Hz
7. Parts of the eye and functions
• Describe the function of each of these parts of
the eye
Part of the eye
cornea
retina
ciliary muscles
suspensory ligament
pupil
Lens
iris
Function
refracts light - bends it as it enters the
eye
contains the light receptors
Controls the shape of the lens
Adjust the shape of the lens to make it
more or less curved
controls how much light enters the eye
focuses light onto the retina
controls how much light enters the pupil
7. Parts of the eye and functions
8. Which diagram shows long sighted,
normal vision and short sightedness?
9. Use data from a graph to calculate
focal length from power.
• Accommodation is another word for power.
What is the focal length of an average 40 year
old?
• D = 1/f
• f = 1/D
• f = 1/4.4
• f = 0.23 m
10. Which direction does centripetal
force act?
• Towards the centre of the circle
11. Name the force that provides the
centripetal force in the 3 examples below:
• Friction
gravity
tension
12. State the factors that affect the size of
the centripetal force acting on an object
• If the speed that the object travels in the
circular motion increases, centripetal force
will increase
• If the mass of the object travelling in circular
motion increases, centripetal force will
increase
• If the radius of the circular motion increases,
the centripetal force will decrease
13. How can you make objects more
stable?
• Lower the centre of mass (gravity)
• Increase the area of the base
• Both of these will ensure that the line of
action from the centre of mass will stay
within the base for longer as the object tips
ensuring that it remains more stable
14. Why do things topple? (with
moments explanation)
• When the line of action from the centre
of mass is outside the area of the base
of the object
• It will create a resultant moment that
will topple the object about the corner
of the object as the pivot
• (In the diagram there is an anticlockwise
moment that will topple the object)
15. Complete the ray diagram to show how a
convex lens produces an image of the object
• Image is: inverted, larger, virtual
16. Complete ray diagrams to show how a
concave lens produces an image of the object
• Image is: diminished, virtual, right way up
17. What is a switch mode transformer
and where would they be used?
• A transformer that uses high frequencies
• Used in mobile phone / tablet chargers
18. What is an advantage of using a
switch mode transformer?
• They are very light compared to iron core
transformers making them easily moveable
• They use very little power when no load is
applied – this is useful for charging batteries
as when they are fully charged the
transformer stops using so much power.
19. How is electric current induced?
• When a magnetic field moves relative to a
wire
• held perpendicular to the field
• a current is induced in the wire
• This is called the dynamo effect
20. Use of transformer equation to find voltage induced from
primary voltage and numbers of primary and secondary turns
in the coil in a diagram
• A transformer has 20 turns on the primary and
400 on the secondary. What is the output
voltage if the input voltage is 500V?
• Vp/Tp = Vs/Ts
• 500/20 = Vs/400
• Vs = (500/20)x400
• Vs = 10000V
21. Explain how potential difference is induced in a
coil of wire from ac current flowing through another
coil inside the second one (but not connected to it)
• An AC current in a coil induces a varying
magnetic field within it
• This varying magnetic field will be moving
relative to the coil of wire within it
• Perpendicular to the coil of the wire
• And so because of the dynamo effect electric
current will be induced
22. What property of liquids allows
hydraulic systems to work?
• They are incompressible
23. Calculation of pressure, area or force from
pressure equation using data in a diagram
P=F/A
P=10/5
P = 2 N/m² or Pa
P=5/4
P = 1.25 N/m² or Pa
24. Calculation of force in a hydraulic
system
• Pressure
remains
constant so
• PA = PB
• 30/0.2 = F/1
• 150 = F
• F = 150N
25. Explain the motor effect
• When a conductor with a current flowing
through it
• is placed perpendicular to a magnetic field
• It will feel a force
• This is the motor effect (sometimes called the
catapult effect)
26. Which way does the wire move?
How do you know?
• The wire will move down
• Because of Fleming’s Left Hand Rule
27. What factors that increase motor
effect
• Increasing the magnetic field
• Increasing the length of wire in the magnetic
field
• Having more electric current flow
28. Explain how a motor works.
• Electric current flows through the
coil so that it flows in one direction
down one side and the other
direction down the other side
• This means that, because of
Flemings Left Hand rule, one side is
forced up whilst the other is forced
down
• This causes the coil to rotate
• Until the coil has turned 90°
• When this happens, the split ring
commutator ensures that no current
flows through the coil for a split
second, allowing the coils
momentum to carry it forward
• When the current starts to flow
again, it starts to force one side up
and the other down so it continues
to rotate
29. What is the total clockwise
moment below?
•
•
•
•
Moment = Force x perpendicular distance
Total clockwise moment = (5x2.5) + (7x5)
Total clockwise moment = 12.5Nm + 35 Nm
Total clockwise moment = 47.5 Nm
30. The anticlockwise moment is 25Nm. What
distance is the force away from the pivot?
Moment = Force x perpendicular distance
Perpendicular distance = Moment / force
Perpendicular distance = 25/5
Perpendicular distance = 5m
31. Explain what the principle of
moments is
• The principle of moments is when there is no
resultant moment:
• the sum of the clockwise moments equals
the sum of the antclockwise moments
Use it to find the force in the example below:
Sum of Anticlockwise moments = sum of clockwise moments
F x 0.25 = 5 x 0.50
F = 2.5 / 0.25
F = 10 N
32. Calculate refracted angle from
refractive index and incident angle
•
•
•
•
•
n = sin1/sin2
1.33 = sin50/sin2
sin2 = sin50/1.33
sin2 = 0.576
2 = 35.2°
33. Calculation of refractive index
from critical angle
• n = 1/sinc
Total internal reflection
n = 1/sinc
1.5 = 1/sinc
sinc = 1/1.5 = 0.67
c = 41.8°
34. What conditions are needed for
total internal reflection to occur
• The light must be with an transparent object
that has a higher refractive index than the
external object
• The angle the travels at must be greater than
the critical angle