MPSC State Service 2021 · CSAT · Question 21 of 73

Passage: Read the passage and answer the questions. The Spectrum of Light The light is kind of electromagnetic spectrum. Radio waves are electromagnetic in nature. Any electromagnetic wave is made up of electric and magnetic fields that travel through space from one place to another. The basic characteristics of the electromagnetic radiation are its frequency and wavelength. To put light waves into perspective with lower radio and other frequencies. The left end of the spectrum is very low frequency electrical signals such as AC power 50 Hz and audio or sound frequencies in 20 Hz to 20 kHz range. These are the lower frequencies that have long wavelengths. Higher up frequency scale to right is wide range of radio frequencies. Radio frequencies range from 10 kHz to 300 GHz. Microwaves extends from 1 to 300 GHz. Even further up the scale we find visible light. The frequency of Optical spectrum is in the range of 3 × 1011 to 3 × 1016 Hz. This includes infrared and ultraviolet as well as visible parts of the spectrum. The visible spectrum is 4.3 × 1014 to 7.5 × 1014 Hz. But we are rarely referred to the frequency of light. Instead we state light in a distance measured in terms of the meters between peaks of wave. Light waves are very short and are usually expressed in Nanometers or microns (one millionth of a meter). Visible light is in the range of 400 to 700 nanometers (nm) or 0.4 to 0.7 micrometers (μm) depending upon colour of light. Short wavelength light is violet and long wavelength light is red colour respectively. Right below the visible light is region of infrared rays cannot be seen. The source of most infrared is heat. Right above visible spectrum is ultraviolet range. Infrared and ultraviolet are included in what we call as optical spectrum. Beyond that are x-rays, gamma rays and cosmic rays. Light travels in a straight line. Light rays emitted by a candle or a light bulb, move out in the straight line in all directions. Light travels at the speed of 300,000, 000 meter/second. i.e.. 1,86, 000 miles/s. The speed of the light depends upon the medium through which light passes. The above speed of light is in the free space means light travelling in air or vacuum. When light travels through glass medium its speed lowers. Light can be manipulated in many ways. Lenses are widely used to focus, enlarge or to decrease the size of the light waves from same source. Lenses permit useful devices such as cameras, binoculars, microscopes, and telescopes. Reflection and refraction are the important characteristics of light. The law of reflection state that angle of reflection is equal to angle of incidence. Refraction is another characteristic of light states that it՚s bending of the light when light rays passes through one medium to another. There is relation between wavelength, frequency and speed of the light. Wavelength is inversely proportional to frequency. Unit of the light is generally expressed in terms of nanometers or micrometers. Light unit is generally expressed in ________.

Reading Comprehension

1. AMeter
2. BCentimeter
3. CMillimeter
4. DNano - MicrometerCorrect