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Class 9–10 · Physics
Physics to save life
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Physics to save life
Lessons in this chapter
Lessons
1Biophysics
Physics explains aspects of body function through forces, flow, waves and electricity. Sensors turn physical changes into measurable signals. Calibration and interference matter; measurements require professional clinical interpretation.
Key relationship
measurement → signal → processing → display
Worked example
A temperature sensor converts a temperature-dependent property into a displayed reading.
Next lesson →2X-rays and CT
Rapidly decelerating electrons can generate X-rays. Differential absorption produces contrast. CT reconstructs slices from many projections. X-rays are ionising, so trained professionals determine justified use and protection.
Key relationship
more absorption → fewer X-rays reach detector
Worked example
Radiograph: projected image; CT: computed cross-sectional reconstruction
Next lesson →3Ultrasonography
Ultrasound sends sound pulses and detects echoes at tissue boundaries. Return time estimates depth; coupling gel reduces air gaps. It is not ionising radiation, but appropriate use and interpretation still matter.
Key relationship
d = vt/2
Worked example
v ≈ 1540 m/s, t = 100 μs ⇒ d = 0.077 m = 7.7 cm
Next lesson →4MRI
MRI uses a strong magnetic field and radiofrequency pulses to measure nuclear signals. Tissue-dependent responses create images. It uses no X-rays, but metallic objects and some implants require strict screening.
Key relationship
magnetic field + radiofrequency excitation + measured response → image
Worked example
Different tissue relaxation properties create contrast.
Next lesson →5ECG and EEG
ECG records potential differences associated with heart activity; EEG records scalp signals associated with brain activity. These are voltage-time records, not photographs. Movement and electrical interference can introduce artefacts.
Key relationship
vertical axis: potential; horizontal axis: time
Worked example
Repeated cardiac cycles 0.8 s apart ⇒ rate = 60/0.8 = 75 per minute
Next lesson →6Fibres, endoscopes and lasers
Optical fibres guide light by total internal reflection. Endoscopes may use fibres or tiny cameras. Lasers can concentrate coherent light into small regions for selected procedures. They require appropriate professional control.
Key relationship
higher-index core + lower-index cladding + sufficient incidence angle
Worked example
Suitable bends retain light; excessive bending can increase loss.
Next lesson →7Radiotherapy and dose
Ionising radiation can damage cellular molecules. Radiotherapy requires careful targeting and protection of healthy tissue. Bq measures source activity, Gy absorbed energy per mass, and Sv a radiation-protection quantity involving biological weighting. This lesson does not prescribe treatment or dose.
Key relationship
1 Gy = 1 J/kg; Bq ≠ Gy ≠ Sv
Worked example
Time, distance and suitable shielding are basic radiation-protection considerations.
Next lesson →Check your understanding
Try answering first, then open the question to compare your reasoning.
1. Formula for depth from an ultrasound echo?
d = vt/2
2. Main field and wave used by MRI?
Strong magnetic field and radiofrequency pulses
3. What does ECG record?
Potential differences associated with cardiac activity over time
4. Unit of absorbed radiation dose?
Gy = J/kg; not Bq
5. Main principle guiding light in optical fibre?
Total internal reflection under suitable index and angle conditions
Sources and scope
Original GetReady teaching notes. The 13 core chapters follow the existing site sequence. Physics to save life is an explicitly labelled older-edition supplement. Check your current book and board instructions for examination scope. Illustrations are schematic. Unless stated otherwise, use g = 9.8 m/s². A physics teacher should review content and edition coverage before it is relied on.