GCSE Physics Unit 3
1. List two applications of physics in the field of medicine.
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2. Draw in the space below diagrams of
(a) a convex lens
(b) a concave lens
Draw in the optical axis. Mark the centre of the lens. (Optical centre)
3. What is meant by
(a) a real image?
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Give an example
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(b) a virtual image
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Give an example
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3. Draw in the space below a ray diagram for a convex lens to show how rays parallel to the
optical axis converge to the focal point. Use arrow heads to show directions before and after
refraction.
4. Define focal length (f). Mark this in the diagram in Q.3
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5. For ray diagrams,
F = Point on axis which is distance f away from the centre of the lens
2F = Point on axis which is distance 2f away from the centre of the lens
Draw in the space below a ray diagram to show how a real image is formed by a convex lens when
the object shown by ↑ is placed
(a) beyond 2F
(b) at 2F
(c) between 2F and F
5. (a) Draw in the space below a ray diagram to show how a virtual image is formed by a convex
lens when the object shown by ↑ is placed between F and the optical centre.
(b) Using the above diagram, explain how a convex lens can be used as a magnifying glass (for
reading).
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6. Define magnification.
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7. The power, P of a lens of focal length f is defined as P = 1/f . What are the units of P when f is
in metres?
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Which type of lens has a negative power? Convex or concave?
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8. What is meant by (a) near point (b) far point as used in optics?
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9. With the help of ray diagrams, explain
(a) Short-sightedness
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(b) Long-sightedness
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10. How is short-sightedness corrected? Use a ray diagram to answer this question.
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How is long-sightedness corrected? Use a ray diagram to answer this question.
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11. Describe using a diagram how do sound waves travel in air. Mark in your diagram
(a) a compression (b) a rarefaction (c) wavelength
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What is (a) the lowest (b) highest frequency of sound humans can hear?
(a) ………………………………………………….
(b)
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12. What are ultrasound waves? How are they produced?
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What is the typical frequency of ultrasound waves used in medical imaging?
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13. What are X-rays? How are they produced?
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14. What is meant by ‘ionising radiations’?
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Why is ionizing radiation harmful to the body?
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Are X-rays ionising?
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Is ultrasound ionising?
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15. What is ‘computerised tomography’ (CT)?
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16.. List two advantages and two disadvantages of using (a) ultrasound (b) X-rays
(c) computerised tomography (CT) scans in medical imaging.
Ultrasound
Advantages
1.……………………………………………………………………………………………………………………………………………………………
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2.……………………………………………………………………………………………………………………………………………………………
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Disadvantages
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X-Rays
Advantages
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Disadvantages
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Computerised Tomography
Advantages
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Disadvantages
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17. Here is a diagram of the eye. Describe the function of each part
■ retina………………………………………………………………………………………………………………………………………..………..
■ lens
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■ cornea
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■ pupil /iris
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■ ciliary muscle
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■ suspensory ligaments ………………………………………………………………………………………………………………..……..
18. The focal length of a lens is determined by:
1. the refractive index of the material from which the lens is made, and
2. the curvature of the two surfaces of the lens.
Refractive index n of a material medium which transmit light is defined as n = sin i /sin r.
Show in a diagram the angles i and r for such a material.
A modified form of the lens maker’s formula for a lens with the same radius of curvature for both
surfaces is
Power = 2 (Refractive Index – 1) ÷ Radius (You don’t have to memorize this!)
For a lens with higher refractive index, the power is …………………………. (higher/lower).
19. What is meant by curvature of a lens surface? Draw a diagram to show arcs of circles with
(i) low curvature and (ii) high curvature.
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For a lens with lower radius (higher curvature), the power is …………………………. (higher/lower).
20. What is meant by critical angle in optics? Draw diagrams to make your answer clear.
Visible light can be sent along optical fibres.
What are optical fibres? Show the path of a ray through such a fibre.
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State two uses for optical fibres, one in medicine and another in communications.
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2. (Communications) ……………………………………………………………………………………………………………………………
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21. The laser is an energy source. The word laser comes from Light Amplification by Stimulated
Emission of Radiation.
What is the speed of laser in a vacuum?
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State a use for laser
1. in medicine
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2. in engineering
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3. in entertainment
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22. Shown below is a diagram of a simple pendulum.
What is meant by ‘one oscillation’ of a pendulum?
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What is meant by periodic time or time period of a pendulum?
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The time period T of a simple pendulum is given by
T = 2 √ (l/g)
where l is the length of the string and g is the acceleration of free fall. Calculate the time period of
a simple pendulum of length 3.0 m. Take g as 10.0 m/s2
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A simple playground swing can be modelled by a simple pendulum. How can the time of swing be
increased?
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23. Define centre of mass.
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Describe briefly how you would find the centre of mass of an irregular shaped card.
Draw diagrams to illustrate your answer.
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24. Define moment (Turning effect).
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What is meant by rotational equilibrium?
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State the principle of moments for a body in rotational equilibrium.
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Using diagrams, explain what for a body is meant by
(a) Stable equilibrium
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(b) Unstable equilibrium
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(c ) Neutral equilibrium
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25. Modern racing cars are designed to have low centre of mass and run on wide tyres. Explain
this.
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26. Define pressure.
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Many liquids are incompressible.
Explain the meaning of ‘incompressible’.
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The pressure in a liquid, at a given depth, is transmitted equally in all directions.
Give an example to demonstrate this. Draw a diagram.
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The hydraulic braking system in a car uses the principle of a force multiplier, provided by an
incompressible liquid. It uses of different cross-sectional areas on the
effort and load sides. This enables a much bigger force applied to the load than the effort force.
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Such a system is shown below.
Complete the following paragraph:
The driver pushes on the brake pedal.
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27. Name three objects that go round in circles
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The moon goes around with the same (linear) speed around the earth in a circle. But the velocity
of the moon changes all the time. How come?
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A body is said to be accelerating when its velocity is changing. So the moon is accelerating all the
time, although its speed remains the same. The direction of this acceleration is always towards the
centre of the circle.
What is the name given to this (centre-seeking) acceleration?
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The resultant force responsible for keeping a body in circular orbit is called centripetal force.
Gravity provides the centripetal force for the moon to be confined to a circular path.
What force provides the centripetal force to the electron in a hydrogen atom to go around the
proton?
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What force provides the centripetal force to keep the iron ball in the diagram below ?
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For a body in circular motion, the centripetal force increases when (a) the mass and (b) the speed
of the object is increased. How will the centripetal force change when the radius is decreased?
28. What is meant by a uniform magnetic field? Explain with a diagram of field lines in a uniform
magnetic field.
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29. Fleming’s left hand rule is shown below:
When a wire is placed in a uniform magnetic field perpendicular to the field lines as shown in the
diagram below, and a current is switched on, a force acts on the wire and the wire begins to move.
Show the direction of the force on the wire with an arrow.
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Current
x = line of force into page
30. A diagram of a simple electric motor is shown below:
What energy changes take place in an electric motor?
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State three ways by which the speed of rotation of the (armature) coil can be increased.
1. ……………………………………………………………………………………………..…………………………………………..........................
2.. ……………………………………………………………………………………………..…………………………………………........................
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3.. ……………………………………………………………………………………………..…………………………………………........................
31. The diagrams below shows two ways of generating electricity. In each, describe how the size
of the induced voltage can be increased.
Method A
Method B
Method A
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2. ……………………………………………………………………………………………….……………………………………………………….....
3. ……………………………………………………………………………………………….……………………………………………………….....
Method B
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2. ……………………………………………………………………………………………….……………………………………………………….....
3. ……………………………………………………………………………………………….……………………………………………………….....
32. Many electrical devices work on voltages smaller than the mains voltage, which is 230V in
England. A transformer is used to reduce or step down the voltage.
Name the parts of the transformer in the diagram below:
How does a transformer work? Fill the missing words:
An …………………………………………………………… current in the primary coil produces
a changing magnetic ………………………. in the iron core and hence in the secondary coil. This
…………………………………………………….. an alternating ………………..…………………
difference across the ends of the ……………………………….……… coil.
The turns ratio equation for a transformer is Vp/Vs = np/ns
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the potential difference across the primary coil in volts, V
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is the potential difference across the secondary coil in volts, V
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is the number of turns on the primary coil
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is the number of turns on the secondary coil
Another equation for in ideal transformer is
Vp Ip = Vs Is
Where Ip is the current in the primary coil in amperes (amps), A and Is is the current in the
secondary coil in amperes (amps), A
What is meant by an ideal transformer?
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In a step-up transformer the potential difference across the secondary coil is …………………….…..
than the potential difference across the primary coil.
In a step-down transformer the potential difference across the ……………………….. coil is less
than the potential difference across the …………..………… coil.
What are switch mode transformers? At what frequencies do they work?
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33. State two uses for switch mode transformers.
1. …………………………………………………………………………………………………………………………………………………………
2.
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State two advantages of using switch mode transformers over traditional transformers?
1. …………………………………………………………………………………………………………………………………………………..………
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2.
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