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In an X-ray machine, X-rays are emitted from an emission spot on a tungsten target - AQA - A-Level Physics - Question 4 - 2021 - Paper 5
Question 4
In an X-ray machine, X-rays are emitted from an emission spot on a tungsten target. Figure 3 shows how a total shadow is produced in the region QR where no X-rays f... show full transcript
Worked Solution & Example Answer:In an X-ray machine, X-rays are emitted from an emission spot on a tungsten target - AQA - A-Level Physics - Question 4 - 2021 - Paper 5
Step 1
To produce a sharp image of a bone, the partial shadow in region PQ must be no more than 0.10 mm wide. Calculate the maximum distance d between a bone and the plate.
Answer
To find the maximum distance , we can use the geometry of the situation. Using similar triangles, we set up the proportion:
Where:
- The width of the shadow is 0.10 mm.
- The height of the emission spot is 1.0 m.
Solving for gives:
Converting units, we know that :
Step 2
Discuss whether an X-ray image of a chest or an X-ray image of a hand is likely to be sharper when exposed to the same X-ray source.
Answer
The sharpness of an X-ray image is largely influenced by the thickness of the object being imaged.
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Chest Imaging: The chest is thicker and has structures that do not have a uniform thickness. Parts of the chest that are closer to the X-ray source will cast a shadow producing an unsharp image, as the front and back cannot be focused at the same time. This results in a blurrier image.
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Hand Imaging: The hand is generally thinner than the chest and can be positioned closer to the X-ray plate. Keeping the hand still during the imaging process allows for a sharper focus, preventing unnecessary blurring due to movement.
Overall, an X-ray image of a hand is likely to be sharper than that of a chest when exposed to the same X-ray source.