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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 calculate the maximum distance between the bone and the plate (d), we can use the formula for similar triangles derived from the setup in the provided figures:
rac{PQ}{d} = rac{0.1 ext{ mm}}{1.0 ext{ m}} \Rearranging this gives:
By converting 0.1 mm to meters, we find:
Substituting to find d:
Thus, the maximum distance d is:
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
An X-ray image of a hand is likely to be sharper than that of a chest. This is due to several factors:
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Thickness of the subject: The chest is thicker compared to the hand, which means more tissue in the way of X-rays. This additional thickness increases the potential for scattering and absorption of the X-rays, leading to a greater possibility of image blurriness.
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Uniformity: The chest is not uniformly thick and contains various structures like bone and soft tissue, each contributing to different levels of shadowing, which can result in an unclear image.
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Focus and alignment: During the X-ray process, the hand can be positioned and aligned more easily compared to the chest, allowing for a more focused image. Additionally, parts of the body like the abdomen and back may interfere with clarity in chest images as they cannot be focused simultaneously.
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Breath control: Patients can be instructed to hold their breath during hand X-rays, reducing movement, whereas breathing during chest X-rays can cause further motion blurriness.
In conclusion, due to thickness, structure uniformity, and better control of movement, the X-ray image of a hand is expected to be sharper than that of a chest.