EM Waves — Set 5
Physics · विद्युत चुंबकीय तरंगें · Questions 41–50 of 50
When light goes from air into a denser medium like glass, its wavelength generally?
Correct Answer: A. Decreases
Light slows down in a denser optical medium. Frequency stays the same at the boundary. Since λ = v/f, wavelength decreases when speed decreases.
X-rays are commonly produced when?
Correct Answer: B. High-speed electrons are suddenly decelerated at a metal target
X-rays can be produced by rapid deceleration of electrons at a target. This process is called bremsstrahlung in many texts. X-rays can also arise from inner-shell electron transitions.
Which statement about gamma rays is generally correct?
Correct Answer: A. They are highly energetic and strongly penetrating
Gamma rays are very high frequency EM waves with high photon energy. Their high energy makes them strongly penetrating and ionizing. Dense materials like lead are often used for shielding.
Many substances glow under ultraviolet light because UV can cause?
Correct Answer: B. Fluorescence
Ultraviolet light can excite electrons in some materials. When electrons fall back, they emit visible light, producing fluorescence. Security markings often use this effect.
Which EM waves are primarily used for AM/FM broadcasting over large areas?
Correct Answer: B. Radio waves
Radio waves are used for AM and FM broadcasting. Their long wavelengths allow efficient transmission and reception with antennas. Different bands are allocated for different services.
Polarizing sunglasses reduce glare mainly because reflected light from horizontal surfaces is often?
Correct Answer: D. Partially horizontally polarized
Reflected light from roads or water is often partially polarized horizontally. Polarizing sunglasses block much of that horizontal component. This reduces glare and improves visual comfort.
The effective length of a half-wave dipole antenna is approximately?
Correct Answer: D. λ/2
A half-wave dipole antenna has length about λ/2. This length supports resonance at the operating frequency. A quarter-wave monopole is about λ/4 above a ground plane.
The energy of a photon of wavelength 500 nm is closest to?
Correct Answer: A. 4.0 × 10^-19 J
Use E = hc/λ with h ≈ 6.63 × 10^-34 J·s and c ≈ 3.0 × 10^8 m/s. For λ = 5.0 × 10^-7 m, E ≈ 4.0 × 10^-19 J. Shorter wavelength photons carry more energy.
Electromagnetic radiation with typical wavelength around 10^-10 m is generally classified as?
Correct Answer: C. X-rays
Wavelengths around 10^-10 m fall in the X-ray region. X-rays have much shorter wavelengths than ultraviolet. Their high energy allows them to penetrate soft tissues to some extent.
Which electromagnetic wave has the shortest wavelength?
Correct Answer: B. Gamma rays
Gamma rays have the shortest wavelength and highest frequency in the electromagnetic spectrum. They are produced during nuclear reactions and radioactive decay. Their wavelengths are less than 10 picometers.