EM Waves — Set 1
Physics · विद्युत चुंबकीय तरंगें · Questions 1–10 of 50
Which relation correctly connects wave speed (c), frequency (f), and wavelength (λ) for an EM wave in vacuum?
Correct Answer: A. c = fλ
For any wave, speed equals frequency times wavelength. For EM waves in vacuum, the speed is c, so c = fλ. If frequency increases, wavelength decreases when c is constant.
In a plane electromagnetic wave, the electric field (E), magnetic field (B), and direction of propagation are?
Correct Answer: A. Mutually perpendicular, with E and B both perpendicular to propagation
In an electromagnetic wave, E and B are at right angles to each other. Both fields are also perpendicular to the direction the wave travels. This shows EM waves are transverse.
Which part of the electromagnetic spectrum has the longest wavelength?
Correct Answer: C. Radio waves
Radio waves have the longest wavelengths in the EM spectrum. Long wavelength means low frequency for the same wave speed. Many communication systems use radio waves.
Which electromagnetic radiation is commonly used in TV remote controls?
Correct Answer: A. Infrared
Remote controls commonly use infrared radiation. Infrared lies just beyond the red end of visible light. It is also associated with heat radiation from warm objects.
Which electromagnetic radiation has the highest frequency?
Correct Answer: D. Gamma rays
Gamma rays have the highest frequencies in the EM spectrum. Higher frequency means higher photon energy. Gamma rays are strongly ionizing compared to visible light.
For an electromagnetic wave in vacuum, the ratio E/B is equal to?
Correct Answer: C. c
In a plane EM wave in vacuum, E divided by B equals the speed of light c. This comes from Maxwell’s equations for waves in free space. It implies E is much larger in magnitude units than B.
The SI unit of frequency is?
Correct Answer: A. Hertz
Frequency is measured in hertz (Hz). One hertz means one cycle per second. Frequency determines the photon energy for EM radiation.
Electromagnetic radiation is produced when electric charges?
Correct Answer: A. Accelerate
The correct answer is 'Accelerate'. Accelerating charges produce electromagnetic waves. A changing electric field creates a changing magnetic field and vice versa. This mutual generation allows the wave to propagate.
Sunburn is most directly associated with which electromagnetic radiation?
Correct Answer: C. Ultraviolet
Ultraviolet radiation can damage skin cells and cause sunburn. UV has higher energy photons than visible light. Sunscreens are designed to reduce UV reaching the skin.
A common operating frequency used in microwave ovens is closest to?
Correct Answer: B. 500 THz
Microwave ovens commonly use radiation near 2.45 GHz. This frequency is in the microwave region of the spectrum. It heats food mainly by interacting with water molecules.