DP Physics Questionbank

• Syllabus

Option C: Imaging

Sub sections and their related questions

Option C: Imaging (Core topics)

• 15M.3.SL.TZ1.21b: (i) Deduce the magnification of the lens. (ii) State and explain the nature of the image formed...
• 15M.3.SL.TZ1.21c: The object is coloured and the image shows chromatic aberration. Explain what is meant by...
• 15M.3.SL.TZ1.21d: Describe how the effects of chromatic aberration may be reduced.
• 15M.3.SL.TZ2.18a: Explain, with reference to the critical angle, what is meant by total internal reflection
• 15M.3.SL.TZ2.18b: In an optic fibre the refractive index of the core is 1.62. The refractive index for the cladding...
• 15M.3.SL.TZ2.18c: State one effect of dispersion on a pulse that has travelled along an optic fibre.
• 15M.3.SL.TZ2.20a: (i) Using the diagram, determine the power of the lens. (ii) On the diagram, construct lines to...
• 15M.3.SL.TZ2.20b: Argus uses an astronomical telescope to observe a telecommunications tower. The height of the...
• 14M.3.SL.TZ1.18a: (i) On the diagram above, construct a ray diagram to locate the position of the image formed by...
• 14M.3.SL.TZ1.18b: The compound microscope in (a) is in normal adjustment so that the final image is formed at the...
• 14M.3.SL.TZ1.19a: Electromagnetic waves propagating in a medium suffer dispersion. Describe what is meant by...
• 15N.3.SL.TZ0.20a.i: On the diagram, construct rays to locate the image of the arrow. The focal points of the lens are...
• 15N.3.SL.TZ0.20a.ii: Anna places a screen at the image position. Outline why she cannot see an image on the screen.
• 15N.3.SL.TZ0.20b: Anna uses the same lens with an illuminated object. She finds that a clear image of the object is...
• 14N.3.SL.TZ0.19a.i: Calculate the critical angle for this optic fibre.
• 14N.3.SL.TZ0.19a.ii: The diagram shows a straight optic fibre. Sketch the passage of a ray of light through the fibre.
• 14N.3.SL.TZ0.19b: The input power to the fibre is 150 mW. The attenuation per unit length of the glass fibre is...
• 14N.3.SL.TZ0.20a.i: Define principal axis.
• 14N.3.SL.TZ0.20a.ii: Construct rays to locate the position of the image.
• 14N.3.SL.TZ0.20a.iii: Identify the nature of the image.
• 14N.3.SL.TZ0.20b.i: The lens is covered with a wide aperture. Using the diagram, sketch the likely appearance of the...
• 14N.3.SL.TZ0.20b.ii: Outline why reducing the size of the aperture will reduce the effects of spherical aberration.
• 14M.3.SL.TZ2.17a: State what is meant by attenuation.
• 14M.3.SL.TZ2.17b: (i)     Determine, using the data, the greatest distance the signal can travel before it must be...
• 14M.3.SL.TZ2.18b: (i)     Define the term near point. (ii)     Outline the advantage of having the image...
• 14M.3.SL.TZ2.18c: (i)     State the separation of the objective lens and the eyepiece lens. (ii)     Determine the...
• 13M.3.SL.TZ1.19a: Calculate the greatest angle of incidence θ that can be used with this fibre.
• 13M.3.SL.TZ1.19b: Sketch the path of the light in the core on the diagram above.
• 13M.3.SL.TZ1.20a: An object is placed 0.10 m in front of the lens. (i) On the diagram, construct rays to locate...
• 13M.3.SL.TZ1.20b: The object in (a) is now moved so that it is located 0.40 m from the lens. Calculate (i) the...
• 13M.3.SL.TZ1.20d: The refractive index of the glass in the lens is greater for blue wavelengths than for red...
• 12M.3.SL.TZ1.17a: (i) Define the angular magnification of a magnifying glass. (ii) Derive an equation for the...
• 12M.3.SL.TZ1.17b: An object is positioned 8.00 cm from a magnifying glass of focal length 15.0 cm. (i) Calculate...
• 12M.3.SL.TZ1.18b: (i) Describe the pattern produced on a screen by a red laser beam incident on a diffraction...
• 11M.3.SL.TZ2.19b: A single lens is used to form a magnified real image of an object. Explain, with reference to the...
• 11M.3.SL.TZ2.20a: Define angular magnification.
• 11M.3.SL.TZ2.20b: A thin converging lens of focal length 4.5 cm is to be used as a magnifying glass. The observer...
• 11M.3.SL.TZ2.20c: Suggest two reasons why, for high magnifications, a combination of lenses is used rather than a...
• 11N.3.SL.TZ0.14d: Digital information that is transmitted along optic fibres is often subject to dispersion due to...
• 11N.3.SL.TZ0.16a: A convex lens used as a magnifying glass has a focal length of fe. Derive an expression for the...
• 11N.3.SL.TZ0.16b: The convex lens in (a) is used as the eyepiece of a compound microscope. An object is placed...
• 11N.3.SL.TZ0.16c: Lenses used in the compound microscope are subject to spherical aberration and chromatic...
• 12N.3.SL.TZ0.19a: State one advantage of the use of an optic fibre rather than a coaxial cable for the transmission...
• 12N.3.SL.TZ0.19b: Suggest why, in transmitting information in an optic fibre, infrared electromagnetic radiation...
• 12N.3.SL.TZ0.19c: A signal is fed into an optic fibre of length L. The noise power at the receiver is Pnoise=4.2...
• 12N.3.SL.TZ0.21b: A converging lens is used as a magnifying glass. On the diagram draw rays to construct the image...
• 12N.3.SL.TZ0.21c: The lens has a focal length f. When the image is formed at the near point, the distance u of the...
• 12N.3.SL.TZ0.21d: A compound microscope consists of an eyepiece lens of focal length 6.0 cm and an objective lens...
• 12M.3.SL.TZ2.18a: On the diagram above, (i) label with the letter F the two focal points of the eyepiece...
• 12M.3.SL.TZ2.18b: The diameter of the Moon subtends an angle of 8.7×10–3 rad at the unaided eye. (i) Determine the...
• 12M.3.HL.TZ2.5b: The input power to a single optic fibre X is 25 mW. The signal needs to be amplified when the...
• 13N.3.SL.TZ0.15a: Construct rays on the diagram to show how the final image is formed.
• 13N.3.SL.TZ0.15b: The intermediate image forms 14.8 cm from the objective lens. The distance between the lenses is...
• 13N.3.SL.TZ0.15c: Outline how the effects of chromatic aberration in the microscope eyepiece can be reduced by...
• 11M.3.SL.TZ1.20a: (i) Define the term focal point. (ii) On the diagram above, construct the paths of two rays in...
• 10N.3.SL.TZ0.F2a: State what is meant by material dispersion.
• 10N.3.SL.TZ0.F2c: (i)     The signal shown below is fed into a monomode optical fibre. On the diagram above,...
• 10N.3.SL.TZ0.G2a: (i)     label, with the symbol \({F_{\text{E}}}\), the position of the other focal point of the...
• 10N.3.SL.TZ0.G2b: In a particular astronomical telescope, the eyepiece lens has a power of 40 dioptres and the...
• 10N.3.SL.TZ0.G2c: In an astronomical telescope the objective is often made up from a diverging and a converging...
• 16M.3.SL.TZ0.9a: Construct a ray diagram for object O. Label the image I.
• 16M.3.SL.TZ0.9b: Estimate the linear magnification of the image.
• 16M.3.SL.TZ0.9c: Outline the advantage of parabolic mirrors over spherical mirrors.
• 16M.3.SL.TZ0.10a: Calculate the magnification of this telescope.
• 16M.3.SL.TZ0.10b: Outline why sign convention is necessary in optics.
• 16M.3.SL.TZ0.10c: A student decides to reverse the positions of the same lenses without changing the separation to...
• 16M.3.SL.TZ0.11a: Draw the path of the ray as it travels through the graded-index optic fibre.
• 16M.3.SL.TZ0.11b: Explain how the graded-index optic fibre reduces waveguide dispersion.
• 16N.3.SL.TZ0.11a: A ray of light is incident on a converging mirror. On the diagram, draw the reflection of the...
• 16N.3.SL.TZ0.11b: The incident ray shown in the diagram makes a significant angle with the optical axis. (i) State...
• 16N.3.SL.TZ0.12a: Identify the nature of the lens.
• 16N.3.SL.TZ0.12b: Determine the distance between the lamp and the lens.
• 16N.3.SL.TZ0.12c: Calculate the focal length of the lens.
• 16N.3.SL.TZ0.12d: The lens is moved to a second position where the image on the screen is again focused. The...
• 16N.3.SL.TZ0.13a: Compare the focal lengths needed for the objective lens in an refracting telescope and in a...
• 16N.3.SL.TZ0.13b: A student has four converging lenses of focal length 5, 20, 150 and 500 mm. Determine the maximum...
• 16N.3.SL.TZ0.13c: There are optical telescopes which have diameters about 10 m. There are radio telescopes with...
• 16N.3.SL.TZ0.13d: The diagram shows a schematic view of a compound microscope with the focal points fo of the...
• 16N.3.SL.TZ0.13e: Image 1 shows details on the petals of a flower under visible light. Image 2 shows the same...
• 16N.3.SL.TZ0.14a: State the main physical difference between step-index and graded-index fibres.
• 16N.3.SL.TZ0.14b: Explain why graded-index fibres help reduce waveguide dispersion.
• 17M.3.SL.TZ1.7a.i: State what is meant by a virtual image.
• 17M.3.SL.TZ1.7a.ii: Show that the image of the object formed by L1 is 12 cm to the right of L1.
• 17M.3.SL.TZ1.7a.iii: The distance between the lenses is 18 cm. Determine the focal length of L2.
• 17M.3.SL.TZ1.7a.iv: On the diagram draw rays to locate the focal point of L2. Label this point F.
• 17M.3.SL.TZ1.7b.i: Explain why, for the final image to form at infinity, the distance between the lenses must be...
• 17M.3.SL.TZ1.7b.ii: The angular diameter of the Moon at the naked eye is 7.8 × 10–3 rad. Calculate the angular...
• 17M.3.SL.TZ1.7c: By reference to chromatic aberration, explain one advantage of a reflecting telescope over a...
• 17M.3.SL.TZ1.8a.i: State two advantages of optic fibres over coaxial cables for these transmissions.
• 17M.3.SL.TZ1.8a.ii: Suggest why infrared radiation rather than visible light is used in these transmissions.
• 17M.3.SL.TZ1.8b: A signal with an input power of 15 mW is transmitted along an optic fibre which has an...
• 17M.3.SL.TZ1.8c: State and explain why it is an advantage for the core of an optic fibre to be extremely thin.
• 17M.3.SL.TZ2.8a.i: On the diagram, sketch the part of wavefront X that is inside the lens.
• 17M.3.SL.TZ2.8a.ii: On the diagram, sketch the wavefront in air that passes through point P. Label this wavefront Y.
• 17M.3.SL.TZ2.8b: Explain your sketch in (a)(i).
• 17M.3.SL.TZ2.8c: Two parallel rays are incident on a system consisting of a diverging lens of focal length 4.0 cm...
• 17M.3.SL.TZ2.9a: Determine the focal length of each lens.
• 17M.3.SL.TZ2.9b: The telescope is used to form an image of the Moon. The angle subtended by the image of the Moon...
• 17M.3.SL.TZ2.9c: State two advantages of the use of satellite-borne telescopes compared to Earth-based telescopes.
• 17M.3.SL.TZ2.10a: The diagram shows a ray of light in air that enters the core of an optic fibre. The ray makes...
• 17M.3.SL.TZ2.10b.i: Identify the features of the output signal that indicate the presence of attenuation and...
• 17M.3.SL.TZ2.10b.ii: The length of the optic fibre is 5.1 km. The input power of the signal is 320 mW. The output...
• 17N.3.SL.TZ0.9a.i: Sketch a ray diagram to show how the magnifying glass produces an upright image.  
• 17N.3.SL.TZ0.9a.ii: State the maximum possible distance from an object to the lens in order for the lens to produce...
• 17N.3.SL.TZ0.9b.i: Determine the position of the image.  
• 17N.3.SL.TZ0.9b.ii: State three characteristics of the image.
• 17N.3.SL.TZ0.9c.i: On the diagram, draw two rays to locate the point Q′ on the image that corresponds to point Q on...
• 17N.3.SL.TZ0.9c.ii: Calculate the vertical distance of point Q′ from the principal axis.
• 17N.3.SL.TZ0.9c.iii: A screen is positioned to form a focused image of point Q. State the direction, relative to Q, in...
• 17N.3.SL.TZ0.9c.iv: The screen is now correctly positioned to form a focused image of point R. However, the top of...
• 17N.3.HL.TZ0.15a: Calculate the maximum angle β for light to travel through the fibre. Refractive index of core   ...
• 17N.3.HL.TZ0.15b: Outline how the combination of core and cladding reduces the overall dispersion in the optic fibres.
• 18M.3.SL.TZ1.8a.i: Identify whether the image is real or virtual.
• 18M.3.SL.TZ1.8a.ii: The lens is 18 cm from the screen and the image is 0.40 times smaller than the object. Calculate...
• 18M.3.SL.TZ1.8a.iii: Light passing through this lens is subject to chromatic aberration. Discuss the effect that...
• 18M.3.SL.TZ1.8b: A system consisting of a converging lens of focal length F1 (lens 1) and a diverging lens (lens...
• 18M.3.SL.TZ1.9a: Calculate the critical angle at the core−cladding boundary.
• 18M.3.SL.TZ1.9b: The use of optical fibres has led to a revolution in communications across the globe. Outline two...
• 18M.3.SL.TZ1.9c.i: Draw on the axes an output signal to illustrate the effect of waveguide dispersion.
• 18M.3.SL.TZ1.9c.ii: Calculate the power of the output signal after the signal has travelled a distance of 3.40 km in...
• 18M.3.SL.TZ1.9c.iii: Explain how the use of a graded-index fibre will improve the performance of this fibre optic system.
• 18M.3.SL.TZ2.8a.i: determine the focal length of the lens.
• 18M.3.SL.TZ2.8a.ii: calculate the linear magnification.
• 18M.3.SL.TZ2.8b: The diagram shows an incomplete ray diagram which consists of a red ray of light and a blue ray...
• 18M.3.SL.TZ2.9a: Identify, with the letter X, the position of the focus of the primary mirror.
• 18M.3.SL.TZ2.9b: This arrangement using the secondary mirror is said to increase the focal length of the primary...
• 18M.3.SL.TZ2.9c: Distinguish between this mounting and the Newtonian mounting.
• 18M.3.SL.TZ2.10a: An optic fibre of refractive index 1.4475 is surrounded by air. The critical angle for the core –...
• 18M.3.SL.TZ2.10b.i: Calculate the maximum attenuation allowed for the signal.
• 18M.3.SL.TZ2.10b.ii: An amplifier can increase the power of the signal by 12 dB. Determine the minimum number of...
• 18M.3.SL.TZ2.10b.iii: The graph shows the variation with wavelength of the refractive index of the glass from which the...
• 18M.3.SL.TZ2.10c: In many places clad optic fibres are replacing copper cables. State one example of how fibre...
• 18M.3.HL.TZ2.13c: It is proposed to build an array of radio telescopes such that the maximum distance between them...

Option C: Imaging (Additional higher level option topics)

• 15M.3.HL.TZ1.19a: Outline how ultrasound is generated for medical diagnostic purposes.
• 15M.3.HL.TZ1.19b: When ultrasound of intensity I0 travels in a medium of acoustic impedance Z1 and is incident on a...
• 15M.3.HL.TZ1.19c: In medical scanning, practitioners have the option of using A-scans or B-scans. Distinguish, with...
• 15M.3.HL.TZ1.20a: Two parallel beams of monochromatic X-rays of the same intensity are incident on equal...
• 15M.3.HL.TZ1.20b: Explain how fluorescent emitters are used to enhance the image formed on a photographic X-ray plate.
• 15M.3.HL.TZ2.20a: (i) X-rays travelling in a medium experience attenuation. State what is meant by...
• 15M.3.HL.TZ2.21a: Define acoustic impedance of a medium.
• 15M.3.HL.TZ2.21b: The acoustic impedances for various media are shown in the table. Ultrasound is incident...
• 15N.3.HL.TZ0.18a.i: Define acoustic impedance.
• 15N.3.HL.TZ0.18a.ii: State the significance of acoustic impedance in the use of ultrasound techniques.
• 15N.3.HL.TZ0.18b: Medical practitioners select the frequency of the ultrasound depending on the diagnosis they are...
• 14M.3.HL.TZ1.21a: Define attenuation coefficient.
• 14M.3.HL.TZ1.21b: The graph below shows the variation of attenuation coefficient μ with photon energy E for X-rays...
• 14N.3.HL.TZ0.22a.i: Define attenuation coefficient.
• 14N.3.HL.TZ0.22a.ii: Calculate the half-value thickness for blood.
• 14N.3.HL.TZ0.22b.i: Calculate the ratio \(\frac{{{I_{{\text{blood}}}}}}{{{I_{{\text{muscle}}}}}}\) for 1 cm of tissue.
• 14N.3.HL.TZ0.22b.ii: Suggest why an X-ray scan does not allow for the differentiation between muscle and blood.
• 14N.3.HL.TZ0.22c: A contrast medium containing iodine is injected into the patient. This increases the attenuation...
• 14N.3.HL.TZ0.22d: X-rays are a form of ionizing radiation. To reduce the danger to a patient, the intensity of...
• 14M.3.HL.TZ2.19c: The intensity of a parallel X-ray beam is reduced to 50% of its initial intensity when it passes...
• 14M.3.HL.TZ2.20a: Define acoustic impedance
• 14M.3.HL.TZ2.20b: (i)     Calculate the speed of ultrasound in muscle. (ii)     Determine the thickness of the...
• 14M.3.HL.TZ2.20c: State one advantage and one disadvantage of using ultrasound of frequency 1 MHz, rather than 3...
• 13M.3.HL.TZ1.21a: The diagram below shows X-rays being used to scan a sample of bone and muscle. (i) Outline how...
• 13M.3.HL.TZ1.21b: The same sample is now investigated with an ultrasound A-scan from the side as shown. (i)...
• 13M.3.HL.TZ2.21a: Define attenuation coefficient.
• 13M.3.HL.TZ2.21b: The graph shows how the attenuation coefficient μ of muscle varies with photon energy E.   In...
• 13M.3.HL.TZ2.22a: Outline the physical principles of NMR imaging.
• 13M.3.HL.TZ2.22b: State two advantages of NMR imaging over computed tomography (CT) imaging.   1.   2.
• 12M.3.HL.TZ1.15b: The table gives the velocity of sound in, and the densities of, the materials. (i) State the...
• 11M.3.HL.TZ2.19a: Use the data from the table to calculate a value for the density of bone.
• 11M.3.HL.TZ2.19b: The fraction F of the intensity of an ultrasound wave reflected at the boundary between two media...
• 11M.3.HL.TZ2.19c: Use your answers in (b) to explain the need for a gel on the patient’s skin.
• 11N.3.HL.TZ0.16a: Outline how ultrasound is produced for use in diagnostic imaging.
• 11N.3.HL.TZ0.16b: In order to look for damage to the chambers of the heart, ultrasound is used to form an image of...
• 11N.3.HL.TZ0.16c: The speed of sound in skin is about five times the speed of sound in air. Given that the density...
• 11N.3.HL.TZ0.16d: Explain, using your answer to (c), why, in using ultrasound for imaging, a layer of gel is placed...
• 11N.3.HL.TZ0.16e: A wide range of frequencies of ultrasound may be used to image internal body organs. The choice...
• 12N.3.HL.TZ0.20a: Define the attenuation coefficient as applied to a beam of X-rays travelling through a medium.
• 12N.3.HL.TZ0.20b: Derive the relationship between the attenuation coefficient μ and the half-value thickness...
• 12N.3.HL.TZ0.20d: Outline why X-rays are not suitable to image an organ such as the liver.
• 13N.3.HL.TZ0.16a: Define attenuation coefficient.
• 13N.3.HL.TZ0.16c: A complete dental record of all the teeth in a patient’s mouth requires about 20 separate X-ray...
• 13N.3.HL.TZ0.16d: The table shows data about the acoustic impedance of some materials that would be involved in the...
• 12M.3.HL.TZ2.19: This question is about nuclear magnetic resonance (NMR). In nuclear magnetic resonance imaging,...
• 12M.3.HL.TZ2.20a: The half-value thickness of the tissue is 4.0 cm. On the axes below, sketch a graph to show the...
• 12M.3.HL.TZ2.20b: Calculate the attenuation coefficient of X-rays for this tissue.
• 12M.3.HL.TZ2.20c: For a different type of tissue, the ratio \(\frac{{{I_t}}}{{{I_0}}}\) is smaller for the same...
• 12M.3.HL.TZ2.20d: Barium has an attenuation coefficient that is much larger than that for human tissue. Explain...
• 11M.3.HL.TZ1.21a: When producing the X-ray photograph, the dose is kept to a minimum by a technique called...
• 11M.3.HL.TZ1.21b: A successful ultrasound scan relies on changes of acoustic impedance around the structure being...
• 10N.3.HL.TZ0.I2a: Define half-value thickness.
• 10N.3.HL.TZ0.I2b: The half-value thickness in tissue for X-rays of a specific energy is 3.50 mm. Determine the...
• 10N.3.HL.TZ0.I2c: For X-rays of higher energy than those in (b), the half-value thickness is greater than 3.50 mm....
• 16M.3.HL.TZ0.15a: X-rays are incident on an aluminium sheet of thickness 8.0 cm. Calculate the fraction of the...
• 16M.3.HL.TZ0.15b: With reference to your answers to (a)(i) and (a)(ii), discuss the advantages of using the...
• 16M.3.HL.TZ0.16a: State one advantage and one disadvantage of magnetic resonance imaging (MRI) compared to X-ray...
• 16M.3.HL.TZ0.16b: Explain why a gradient field is required in nuclear magnetic resonance (NMR) imaging.
• 16N.3.HL.TZ0.19a: Show that the attenuation coefficient for bone of density 1800 kg m–3, for X-rays of 20 keV, is...
• 16N.3.HL.TZ0.19b: The density of muscle is 1200 kg m–3. Calculate the ratio of intensities to compare, for a beam...
• 16N.3.HL.TZ0.19c: Suggest why more energetic beams of about 150 keV would be unsuitable for imaging a bone–muscle...
• 16N.3.HL.TZ0.20a: State the property of protons used in nuclear magnetic resonance (NMR) imaging.
• 16N.3.HL.TZ0.20b: Explain how a gradient field and resonance are produced in NMR to allow for the formation of...
• 17M.3.HL.TZ1.13a: Outline why the fracture in a broken bone can be seen in a medical X-ray image.
• 17M.3.HL.TZ1.13b: The diagram shows X-rays incident on tissue and bone. The thicknesses of bone and tissue are...
• 17M.3.HL.TZ1.13c.i: the large uniform magnetic field applied to the patient.
• 17M.3.HL.TZ1.13c.ii: the radio-frequency signal emitted towards the patient.
• 17M.3.HL.TZ1.13c.iii: the non-uniform magnetic field applied to the patient.
• 17M.3.HL.TZ2.15a: State a typical frequency used in medical ultrasound imaging.
• 17M.3.HL.TZ2.15b: Describe how an ultrasound transducer produces ultrasound.
• 17M.3.HL.TZ2.15c.i: Calculate the acoustic impedance Z of muscle.
• 17M.3.HL.TZ2.15c.ii: Ultrasound of intensity 0.012 W\(\,\)cm–2 is incident on a water–muscle boundary. The acoustic...
• 17M.3.HL.TZ2.16: In nuclear magnetic resonance (NMR) imaging radio frequency electromagnetic radiation is detected...
• 17N.3.HL.TZ0.16a: Show that the attenuation coefficient of lead is 60 cm–1.
• 17N.3.HL.TZ0.16b: A technician operates an X-ray machine that takes 100 images each day. Estimate the width of the...
• 18M.3.HL.TZ1.14a: Outline how ultrasound is generated for medical imaging.
• 18M.3.HL.TZ1.14b: Describe one advantage and one disadvantage of using high frequencies ultrasound over low...
• 18M.3.HL.TZ1.14c: Suggest one reason why doctors use ultrasound rather than X-rays to monitor the development of a...
• 18M.3.HL.TZ1.14d.i: Calculate the density of skin.
• 18M.3.HL.TZ1.14d.ii: Explain, with appropriate calculations, why a gel is used between the transducer and the skin.
• 18M.3.HL.TZ2.15a: Outline the formation of a B scan in medical ultrasound imaging.
• 18M.3.HL.TZ2.15b.i: State what is meant by half-value thickness in X-ray imaging.
• 18M.3.HL.TZ2.15b.ii: A monochromatic X-ray beam of energy 20 keV and intensity I0 penetrates 5.00 cm of fat and then...
• 18M.3.HL.TZ2.15b.iii: Compare the use of high and low energy X-rays for medical imaging.