Q4. Assertion: microwaves are used in the radar systems of aircraft navigation. Reason: microwaves have short wavelengths. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion: NCERT says their short wavelengths make microwaves suitable for radar (NCERT page 209).
Q5. Name the part of the spectrum used (a) to kill germs in water purifiers, (b) in TV remote controls, (c) to destroy cancer cells, (d) in aircraft radar.
(a) Ultraviolet. (b) Infrared. (c) Gamma rays (X-rays also treat some cancers). (d) Microwaves (NCERT pages 209–211).
Q6. The AM radio band runs from 530 kHz to 1710 kHz. Find the range of wavelengths.
λ = c/ν: 3 × 108/(530 × 103) ≈ 566 m and 3 × 108/(1710 × 103) ≈ 175 m (NCERT page 209; Eq. [8.9(b)], page 207).
Q7. Find the photon energy of X-rays of wavelength 0.1 nm, in eV.
E = hc/λ ≈ 1240 eV nm/0.1 nm ≈ 1.2 × 104 eV, about 12 keV (NCERT Exercise 8.9, page 214).