EM Waves — Set 4
Physics · विद्युत चुंबकीय तरंगें · Questions 31–40 of 50
Optical fiber communication most commonly uses which region of EM waves?
Correct Answer: D. Infrared (near IR)
Fiber optics commonly use near-infrared wavelengths. These wavelengths experience low loss in glass fibers. Typical telecom windows are around 1.3 μm and 1.55 μm.
In Maxwell’s theory, displacement current is associated with?
Correct Answer: C. A changing electric field producing a magnetic effect
Displacement current arises from a changing electric field. It helps explain magnetic fields in regions with no conduction current, like a capacitor gap. This completed Maxwell’s correction to Ampere’s law.
Electromagnetic waves carry momentum, so they can exert?
Correct Answer: C. Radiation pressure
EM waves transfer momentum to surfaces they strike. This creates a small force called radiation pressure. Solar sails conceptually use this pressure for propulsion.
The ozone layer is especially important because it strongly absorbs much of the?
Correct Answer: B. Ultraviolet
Ozone absorbs a significant portion of ultraviolet radiation from the Sun. This reduces harmful UV reaching Earth’s surface. UV has higher photon energy than visible light.
Microwaves heat food mainly because they?
Correct Answer: C. Cause rotation of polar molecules like water
Microwaves make polar molecules rotate rapidly in an alternating field. This motion converts energy into heat inside the food. Water content strongly affects microwave heating.
An EM wave has frequency 3.0 × 10^8 Hz. Its wavelength in vacuum is?
Correct Answer: A. 1 m
Use λ = c/f with c = 3.0 × 10^8 m/s and f = 3.0 × 10^8 Hz. This gives λ = 1 m. In vacuum, wavelength is directly set by frequency.
A transmitter operates at 150 MHz. The wavelength in vacuum is closest to?
Correct Answer: C. 2 m
Use λ = c/f with c = 3.0 × 10^8 m/s and f = 1.5 × 10^8 Hz. This gives λ = 2 m. Antenna sizes are often related to fractions of wavelength.
Thermal imaging cameras mainly detect which EM radiation?
Correct Answer: C. Infrared
Thermal cameras detect infrared radiation emitted by warm objects. Hotter objects generally emit more infrared power. This is related to blackbody radiation principles.
The speed of EM waves in vacuum can be written as?
Correct Answer: A. c = 1/√(μ0ε0)
Maxwell’s theory gives c = 1/√(μ0ε0) for vacuum. Here μ0 is permeability and ε0 is permittivity of free space. This links electromagnetic constants to the speed of light.
The SI unit of wavelength is?
Correct Answer: B. Meter
Wavelength is a measure of distance between repeating wave points. The SI unit of distance is the meter. Wavelength is inversely related to frequency when wave speed is fixed.