Match the different types of Electro Magnetic Waves and their detections
| LIST I | LIST II |
| Electro Magnetic waves | Detection of Electromagnetic wave |
| A. Light | I. Receiver's aerial |
| B. Infra red | II. Point contact diodes |
| C. Radiowave | III. Photocells |
| D. Microwave | IV. Thermopiles |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A-III, B-IV, C-I, D-II
Each band of the electromagnetic spectrum is detected through the effect it produces most strongly in matter, and that depends on its wavelength.
(A) Light — this matches (III) Photocells. Visible light ejects electrons from a suitable surface by the photoelectric effect, and a photocell turns this into a current (the eye and photographic film also detect light).
(B) Infra red — this matches (IV) Thermopiles. Infrared radiation is absorbed as heat, and a thermopile (or a bolometer) detects it through the rise in temperature it produces.
(C) Radiowave — this matches (I) Receiver's aerial. The oscillating field of a radio wave drives oscillating currents in the receiving aerial, which the receiver then picks up.
(D) Microwave — this matches (II) Point contact diodes. Microwaves have frequencies too high for the usual circuit detectors, and point contact diodes are used to rectify and detect them.
NCERT (2026-27):
Gamma Rays – “… Table 8.1 summarises different types of electromagnetic waves, their production and detections. As mentioned earlier, the demarcation between different regions is not sharp and there are overlaps.”
| Type | Wavelength range | Production | Detection |
| Radio | > 0.1 m | Rapid acceleration and decelerations of electrons in aerials | Receiver’s aerials |
| Microwave | 0.1m to 1 mm | Klystron valve or magnetron valve | Point contact diodes |
| Infra-red | 1mm to 700 nm | Vibration of atoms and molecules | Thermopiles Bolometer, Infrared photographic film |
| Light | 700 nm to 400 nm | Electrons in atoms emit light when they move from one energy level to a lower energy level | The eye Photocells Photographic film |
| Ultraviolet | 400 nm to 1nm | Inner shell electrons in atoms moving from one energy level to a lower level | Photocells Photographic film |
| X-rays | 1nm to 10−3 nm | X-ray tubes or inner shell electrons | Photographic film Geiger tubes Ionisation chamber |
| Gamma rays | <10−3 nm | Radioactive decay of the nucleus | -do- |