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Doc Brown's Physics AQA GCSE Science-PHYSICS Revision Notes

Physics Unit P3.1 Medical applications of physics Study Notes

PHYSICS UNIT 3 Physics 3 for GCSE Triple Award Science or GCSE Physics

REVISION NOTES GUIDE SUMMARY: What do you need to know for the examinations? What do you need to able to do in the exams? In AQA GCSE Science A examinations HT means for higher tier students only. Sorry, but I don't have much time to answer questions, but if you see any apparent errors or wish to comment, please email me. All my notes, learning objectives, comments for exam revision are based on the official AQA GCSE Science A Key Stage 4 syllabus specification.

AQA GCSE Science PHYSICS 3 Unit P3.1 Medical applications of physics

  • Appreciate that physics has many applications in the field of medicine.

  • Know that these include the uses of X-rays and ultrasound for scanning, and of light for image formation with lenses and endoscopes

  • You should be able to use your skills, knowledge and understanding to:

    • draw and interpret ray diagrams in order to determine the nature of the image,

      • In ray diagrams:

        • will represent a convex lens

        • will represent a concave lens

    • evaluate the use of different lenses for the correction of defects of vision,

    • compare the medical use of ultrasound and X rays,

      • you should understand that some of the differences in use are because ultrasound waves are non-ionising and X rays are ionising,

    • evaluate the advantages and disadvantages of using ultrasound, X-rays and Computerised Tomography (CT) scans,

      •  limited to safety issues and the quality of image formed.


AQA GCSE Science PHYSICS Unit P3.1.1 X-rays

  • a) You should know and understand that X-rays are part of the electromagnetic spectrum.

    • X-rays have a very short wavelength and cause ionisation,

    • The properties of X-rays you should know about include:

      • they affect a photographic film in the same way as light,

      • they are absorbed by metal and bone

      • they are transmitted by healthy tissue,

      • their wavelength is of the same order of magnitude as the diameter of an atom.

  • b) Know that X-rays can be used to diagnose and treat some medical conditions.

    • Know about examples of their use including CT scans, bone fractures, dental problems and killing cancer cells.

    • Know that the use of charge-coupled devices (CCDs) allows images to be formed electronically.

  • c) Know the precautions to be taken when X-ray machines and CT scanners are in use.


AQA GCSE Science PHYSICS Unit P3.1.2 Ultrasound

  • a) Know and understand that electronic systems can be used to produce ultrasound waves, which have a frequency higher than the upper limit of hearing for humans.

    • You should know that the range of human hearing is about 20 Hz to 20 000 Hz.

  • b) Know and ultrasound waves are partially reflected when they meet a boundary between two different media.

    • Know that the time taken for the reflections to reach a detector can be used to determine how far away such a boundary is.

  • c) Be able to calculate the distance between interfaces in various media.

    • Be able to use the equation

    • s = v x t

    • s is distance in metres, m

    • v is speed in metres per second, m/s

    • t is time in seconds, s

      • You may be required to use data from diagrams of oscilloscope traces.

  • d) Know how ultrasound waves can be used in medicine.

    • Examples you should know about include pre-natal scanning and the removal of kidney stones.


AQA GCSE Science PHYSICS Unit P3.1.3 Lenses

  • a) Know and understand that refraction is the change of direction of light as it passes from one medium to another.

  • b) Know and understand that a lens forms an image by refracting light.

  • c) Know and understand that in a convex or converging lens, parallel rays of light are brought to a focus at the principal focus.

    • Know that the distance from the lens to the principal focus is called the focal length.

    • Know the formula:

      • refractive index = sin i / sin r

      • i is the angle of incidence, r is the angle of refraction

  • d) Know and understand that the nature of an image is defined by its size relative to the object, whether it is upright or inverted relative to the object and whether it is real or virtual.

  • e) Know the nature of the image produced by a converging lens for an object placed at different distances from the lens.

  • f) Know and understand the use of a converging lens as a magnifying glass.

  • g) Know the nature of the image produced by a concave or diverging lens.

  • h) Be able to construct ray diagrams to show the formation of images by converging and diverging lenses.

    •  You may be asked to complete ray diagrams drawn on graph paper.

  • i) Know that the magnification produced by a lens is calculated using the equation:

    • magnification = image height / object height


AQA GCSE Science PHYSICS Unit P3.1.4 The eye

  • a) Know the structure and function of the parts of the eye.

    • You should know about the function of the:

      • retina

      • lens

      • cornea

      • pupil / iris

      • ciliary muscle

        • You should understand how the action of the ciliary muscle causes changes in the shape of the lens, which allows the light to be focused at varying distances.

      • suspensory ligaments.

  • b) Know and understand that correction of vision using convex and concave lenses to produce an image on the retina:

    • long sight, caused by the eyeball being too short, or the eye lens being unable to focus,

    • short sight, caused by the eyeball being too long, or the eye lens being unable to focus.

  • c) Appreciate the concept of range of vision - the eye can focus on objects between the near point and the far point.

    • You should know that the near point is approximately 25 cm and the far point is infinity

  • d) Be able to compare the structure of the eye and the camera.

    • You should be aware that the film in a camera or the CCDs in a digital camera is the equivalent of the retina in the eye.

  • e) Know that the power of a lens is given by:

    • P = 1 / f

    • P is power in dioptres, D

    • f is focal length in metres, m

    • You should know that the power of a converging lens is positive and the power of a diverging lens is negative.

  • f) The focal length of a lens is determined by: the refractive index of the material from which the lens is made, and the curvature of the two surfaces of the lens.

  • g) HT only: Know that for a given focal length, the greater the refractive index of the glass, the flatter the lens.

    • HT only: Know and understand that this means that the lens can be manufactured thinner.


AQA GCSE Science PHYSICS Unit P3.1.5 Other applications using light

  • a) Know and understand that phenomena of total internal reflection and critical angle.

    • You need to understand the concept of critical angle but knowledge of the values of critical angles is not required.

    • HT only: Be able to use the formula:

    • refractive index = 1 / sin c

    • c is the critical angle

  • b) Know and understand that visible light can be sent along optical fibres because of total internal reflection.

    • Examples of use you should know about include the endoscope for internal imaging,

  • c) The laser as an energy source for cutting, cauterising and burning.

    • You should know about its application and use in eye surgery,

    • but knowledge of how lasers work is not required.


  • Practical work in unit 3.1 to help develop your skills and understanding may have included the following:

    • demonstrating the range of frequencies audible to the human ear, using a signal generator, loudspeaker and oscilloscope

    • demonstrating long and short sight by placing a screen, not at the focal point, and rectifying the image through the use of appropriate lenses

    • using a round bottom flask filled with a solution of fluoresce in to represent the eye

    • investigating total internal reflection using a semi-circular glass block.

  • AQA GCSE PHYSICS

  • When revising, these pages provide you with a summary of what you need to know and be able to do.

  • BUT remember, your primary source of revision are your class notes, investigations and AQA GCSE science textbooks.

  • AQA GCSE Triple Award Separate PHYSICS UNIT P3 Index:


GCSE Science-Physics courses AQA GCSE Science A PHYSICS  *  EDEXCEL GCSE Science PHYSICS

OCR GCSE 21st Century Science A PHYSICS  *  OCR GCSE Gateway Science A PHYSICS


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