C. Imaging

C. Imaging

Core

C.1 – Introduction to imaging

Nature of science:

• Deductive logic: The use of virtual images is essential for our analysis of lenses and mirrors.

Understandings:

• Thin lenses

• Converging and diverging lenses

• Converging and diverging mirrors

• Ray diagrams

• Real and virtual images

• Linear and angular magnification

• Spherical and chromatic aberrations

Applications and skills:

• Describing how a curved transparent interface modifies the shape of an incident wavefront

• Identifying the principal axis, focal point and focal length of a simple converging or diverging lens on a scaled diagram

• Solving problems involving not more than two lenses by constructing scaled ray diagrams

• Solving problems involving not more than two curved mirrors by constructing scaled ray diagrams

• Solving problems involving the thin lens equation, linear magnification and angular magnification

• Explaining spherical and chromatic aberrations and describing ways to reduce their effects on images

C.2 – Imaging instrumentation

Nature of science:

• Improved instrumentation: The optical telescope has been in use for over 500 years. It has enabled humankind to observe and hypothesize about the universe. More recently, radio telescopes have been developed to investigate the electromagnetic radiation beyond the visible region. Telescopes (both visual and radio) are now placed away from the Earth’s surface to avoid the image degradation caused by the atmosphere, while corrective optics are used to enhance images collected at the Earth’s surface. Many satellites have been launched with sensors capable of recording vast amounts of data in the infrared, ultraviolet, X-ray and other electromagnetic spectrum ranges.

Understandings:

• Optical compound microscopes

• Simple optical astronomical refracting telescopes

• Simple optical astronomical reflecting telescopes

• Single-dish radio telescopes

• Radio interferometry telescopes

• Satellite-borne telescopes

Applications and skills:

• Constructing and interpreting ray diagrams of optical compound microscopes at normal adjustment

• Solving problems involving the angular magnification and resolution of optical compound microscopes

• Investigating the optical compound microscope experimentally

• Constructing or completing ray diagrams of simple optical astronomical refracting telescopes at normal adjustment

• Solving problems involving the angular magnification of simple optical astronomical telescopes

• Investigating the performance of a simple optical astronomical refracting telescope experimentally

• Describing the comparative performance of Earth-based telescopes and satellite-borne telescopes

C.3 – Fibre optics

Nature of science:

• Applied science: Advances in communication links using fibre optics have led to a global network of optical fibres that has transformed global communications by voice, video and data.

Understandings:

• Structure of optic fibres

• Step-index fibres and graded-index fibres

• Total internal reflection and critical angle

• Waveguide and material dispersion in optic fibres

• Attenuation and the decibel (dB) scale

Applications and skills:

• Solving problems involving total internal reflection and critical angle in the context of fibre optics

• Describing how waveguide and material dispersion can lead to attenuation and how this can be accounted for

• Solving problems involving attenuation

• Describing the advantages of fibre optics over twisted pair and coaxial cables

Additional higher level

C.4 – Medical imaging

Nature of science:

• Risk analysis: The doctor’s role is to minimize patient risk in medical diagnosis and procedures based on an assessment of the overall benefit to the patient. Arguments involving probability are used in considering the attenuation of radiation transmitted through the body.

Understandings:

• Detection and recording of X-ray images in medical contexts

• Generation and detection of ultrasound in medical contexts

• Medical imaging techniques (magnetic resonance imaging) involving nuclear magnetic resonance (NMR)

Applications and skills:

• Explaining features of X-ray imaging, including attenuation coefficient, half-value thickness, linear/mass absorption coefficients and techniques for improvements of sharpness and contrast

• Solving X-ray attenuation problems

• Solving problems involving ultrasound acoustic impedance, speed of ultrasound through tissue and air and relative intensity levels

• Explaining features of medical ultrasound techniques, including choice of frequency, use of gel and the difference between A and B scans

• Explaining the use of gradient fields in NMR

• Explaining the origin of the relaxation of proton spin and consequent emission of signal in NMR

• Discussing the advantages and disadvantages of ultrasound and NMR scanning methods, including a simple assessment of risk in these medical procedures