Choose suitable electromagnetic regions for satellite communication, thermal imaging through smoke and imaging a broken bone, explaining each. (a) Calculate frequency of 3.0 cm satellite radiation using c = 3.0 × 10⁸ m/s. (b) Order the chosen regions by photon energy. (c) Explain one hospital safety control. (d) State what all three regions have in common when travelling through a vacuum.

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Microwave, infrared and X-ray respectively; 3.0 cm gives 1.0 × 10¹⁰ Hz; energy order X-ray > infrared > microwave. Microwaves in suitable bands pass through the atmosphere and can be directed with dishes for satellite communication. Convert 3.0 cm to 0.030 m before calculation. Frequency f = c/λ = 3.0 × 10⁸/0.030 = 1.0 × 10¹⁰ Hz. Warm surfaces emit infrared related to temperature, so infrared cameras map heat. X-rays are absorbed more strongly by bone than soft tissue, producing detector contrast. Photon energy E = hf increases with frequency, so X-ray has greatest energy, then infrared, then microwave. All travel at c in vacuum. Ionising X-ray exposure is minimised using the lowest diagnostic exposure, beam collimation, shielding, distance and avoiding unnecessary repeats; benefit must justify risk.

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