Science · X-Factor Notes
Optics revision notes for UPPCS Prelims.
29 revision facts
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Light Definition | Light is an electromagnetic radiation that lies between the infrared and ultraviolet parts of the electromagnetic spectrum. It is invisible itself but aids in the visibility of matter. | |
| Light Characteristics | Light has a dual nature (it behaves both as a wave and as a particle) and travels in a straight line. It can travel through a vacuum, unlike sound waves. | |
| Speed of Light | The speed of light is 3 x 108 m/sec. Light is generally considered to have a greater velocity than sound. | |
| Wavelength Range (Visible) | The wavelength of visible light ranges from 3900 Å to 7800 Å or about 4 x 10-7 to 7 x 10-7metre. The visible range of solar radiation is 400 to 700 nm. | |
| Appearance of Straight Travel | Light appears to travel in a straight line because its wavelength is very small. | U.P.P.S.C. (R.I.) 2014 |
| Variables During Refraction | When light passes from one medium to another (e.g., air to glass), its frequency does not change. The wavelength and velocity are affected. | I.A.S. (Pre) 2001, UPPCS (Mains) 2003 |
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Diamond Shining | The extraordinary shining of a properly cut diamond is due to its higher refractive index. | I.A.S. (Pre) 1994 |
| Optical Fibre Principle | Fibre optics uses the phenomenon of Total Internal Reflection for the transmission of light energy. This communication system is free from radio frequency interference and has low power consumption. | UPPCS (Pre) 2019, UPPCS (Mains) 2015 |
| Mirage | The mirage phenomenon is caused by the total internal reflection of light. | UPPCS (Pre) 2012, UPPCS (Pre) 1995 |
| Air Bubble in Water | An air bubble inside water behaves as a divergent lens (concave lens). | UPPCS (Pre) 2002 |
| Concave Mirror Uses | Used by dentists to produce magnified, upright images of teeth (when the object is closer than the focal length). Also used in searchlights and car headlights for sharp light beams. | UPPCS (Mains) 2009, UPPCS(Pre) 2013 |
| Convex Mirror Uses | Used as a rear-view side mirror in vehicles because they are curved outwards, providing a wider field of view and forming erect and diminished images. | U.P. P.C.S. (Pre) 1991, UPPCS (Pre) 2015, U.P.P.C.S (Pre) 2011, UPPCS (Mains) 2010 |
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Color Determination | The color of light is determined by its wavelength. | UPPCS (Mains) 2014, UPPCS(Pre) 2012 |
| Wavelength Extremes | Red color has the longest wavelength in the visible spectrum; Violet color has the shortest wavelength. | U.P.R.O./A.R.O. (Mains) 2014 |
| Energy and Color | The energy of a wave is inversely proportional to its wavelength. Blue light has the highest energy among visible light options compared to green, red, or yellow light. | I.A.S. (Pre) 2009 |
| Deviation by Prism | The speed of red light is maximum in glass, thus the red color is least deviated by a glass prism. | U.P. R.O./A.R.O. (Pre) (Re. Exam) 2016 |
| Sunset/Sunrise Color | The red color of the Sun at sunset and sunrise is due to the scattering of light. | UPPCS (Mains) 2013, U.P. P.C.S. (Pre) 1992 |
| Sky Appearance at Altitude | For passengers flying at high altitudes, the sky appears dark because scattering is not prominent at such heights. | |
| Dispersion | Dispersion of light (splitting white light into component colors) is possible by a prism. Sunlight consists of seven colors (VIBGYOR). | UPPCS (Mains) 2015 |
| Primary Colors (Light) | The primary colors of light are Red, Green, and Blue. When mixed in equal proportions, they produce white color light. |
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Image on Retina | The image formed on the retina is real, inverted, and smaller than the object. Light rays are transformed into neural impulses at the retina. | UPPCS (Pre) 1997, UPPCS (Pre) 1995, UPPCS (Spl.) (Mains) 2004 |
| Retina Analogy | The retina operates similarly to the film inside a traditional camera. | U.P.P.C.S (Pre) 2011 |
| Eye Focusing (Accommodation) | The focal length of the eye lens is changed by altering its curvature/convexity, controlled by the ciliary muscles. | U.P.P.S.C. (R.I.) 2014 |
| Least Distance of Vision | The minimum distance for clear vision for a normal healthy eye is about 25 cm. | UPPCS (Mains) 2008 |
| Myopia (Near-sightedness) | Distant objects appear blurred. Corrected by using a Concave lens. | UPPCS (Mains) 2011, U.P. Lower Sub. (Pre) 2002, UPPCS (Mains) 2008, UPPCS (Mains) 2013 |
| Hypermetropia (Far-sightedness) | Near objects are blurry. Image is focused behind the retina. Corrected by using a Convex lens. | U.P. R.O./A.R.O. (Mains) 2017 |
| Lens Power Unit | The power of a lens is measured in Dioptre. | |
| Telescope Resolution | As the diameter of the objective lens of a telescope increases, the resolution (resolving power) increases. | |
| Final Image in Astronomical Telescope | The final image formed by an astronomical telescope is typically virtual and highly magnified. | UPPCS (Mains) 2013 |
