Correct Option
Statement 3: Radio waves are a form of electromagnetic radiation. They are produced by the acceleration of electric charges, typically through rapidly oscillating electrical currents in devices like antennas. These oscillations generate propagating electric and magnetic fields that constitute radio waves.
Statement 4: Police radar systems employ the Doppler effect to measure the speed of moving vehicles. These devices emit short radio waves which are reflected by the target vehicle. The frequency of the reflected waves changes relative to the emitted waves due to the vehicle's motion. This frequency shift, known as the Doppler shift, is analyzed to accurately calculate the vehicle's speed and detect overspeeding.
Incorrect Options
Statement 1: According to Rayleigh scattering, the intensity of scattered light is inversely proportional to the fourth power of its wavelength (I ∝ 1/λ⁴). This principle indicates that light of shorter wavelengths (e.g., blue and violet) is scattered much more significantly than light of longer wavelengths (e.g., red). Therefore, the statement that longer wavelengths are scattered much more is incorrect.
Statement 2: The speed of light in a medium is determined by the medium's refractive index. The refractive index of water is approximately 1.33. The speed of light in water (v) is given by v = c/n, where c is the speed of light in vacuum and n is the refractive index. Thus, v ≈ c/1.33 ≈ 0.75c. The statement's value of 0.95 times the speed in vacuum is therefore incorrect.