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Q1. The deviation of light occurs due to
The deviation of light occurs due to inclined (non-parallel) refracting surfaces, like those of a prism. When light enters a prism, it bends at the first surface and then bends again at the second surface. Because the surfaces are inclined to each other, the light is deviated from its original path. In a glass slab (parallel surfaces), light is displaced but not deviated.
Q2. A rainbow is always formed in a direction
A rainbow is always formed in a direction opposite to the Sun. This is because the Sun’s light must enter raindrops and be reflected back towards the observer. For this to happen, the observer must be between the Sun and the raindrops, with the Sun behind them and the rainbow in front of them.
Q3. The refracting medium in atmospheric refraction is
The refracting medium in atmospheric refraction is the Earth’s atmosphere (air). Atmospheric refraction occurs when light passes through different layers of air with varying temperatures and densities. These changes in air density cause light to bend as it travels through the atmosphere.
Q4. The apparent wavering of objects above a fire is due to
The apparent wavering or flickering of objects seen through hot air above a fire is due to atmospheric refraction. Hot air has a different density (lower) than the surrounding cooler air, causing light to refract differently. As the hot air rises and moves, the refraction changes, making objects appear to waver or flicker.
Q5. The spectrum produced by a prism is
The spectrum produced by a prism is a continuous band of colours (VIBGYOR). When white light passes through a prism, it is dispersed into seven colours: Violet, Indigo, Blue, Green, Yellow, Orange, and Red. The colours blend into each other gradually, creating a continuous band.
Q6. A triangular glass prism has
A triangular glass prism has two triangular bases and three rectangular lateral surfaces. The two triangular bases are parallel to each other. Light enters through one rectangular face and exits through another, bending as it passes through the prism. The angle between the two triangular bases is the angle of the prism.
Q7. Atmospheric refraction occurs because the air layers are
Atmospheric refraction occurs because the air layers are non-uniform, meaning they have different temperatures, densities, and refractive indices. These variations cause light to bend as it passes through the atmosphere. If the atmosphere were uniform, there would be no atmospheric refraction.
Q8. A rainbow is a natural example of
A rainbow is a natural example of dispersion of sunlight through raindrops. However, it also involves refraction and total internal reflection. The primary phenomenon is dispersion, where white sunlight is split into its component colours (VIBGYOR) as it passes through raindrops.
Q9. The band of colours produced by dispersion is called
The band of colours produced by dispersion is called a spectrum. A spectrum consists of seven colours: Violet, Indigo, Blue, Green, Yellow, Orange, and Red (VIBGYOR). The spectrum is formed when white light is split into its component colours, like in a prism or rainbow.
Q10. Different colours bend differently because they have different
Different colours (wavelengths) of light bend differently because they have different speeds in a medium like glass. Violet light (shorter wavelength) travels slower in glass and bends more. Red light (longer wavelength) travels faster and bends less. This difference in speed causes dispersion.
Q11. Water droplets act like
In a rainbow, water droplets act like small prisms. When sunlight enters a raindrop, it is refracted, dispersed into colours, and undergoes total internal reflection inside the drop. The colours then emerge at different angles, creating a rainbow. Each raindrop acts like a tiny prism.
Q12. Twinkling of stars is caused by
The twinkling of stars is caused by atmospheric refraction. As starlight passes through different layers of Earth’s atmosphere, it is continuously refracted due to changes in air density and temperature. This causes the apparent position and brightness of the star to fluctuate, making it twinkle.
Q13. Twinkling of stars occurs on a
The twinkling of stars occurs on a large scale because it involves the entire Earth’s atmosphere. Starlight travels through kilometres of atmosphere before reaching our eyes. The continuously changing conditions in the atmosphere cause the twinkling effect on a massive, large scale.
Q14. Isaac Newton first obtained the spectrum of sunlight using
Isaac Newton first obtained the spectrum of sunlight using a glass prism. In 1666, Newton passed a narrow beam of sunlight through a prism and observed the spectrum of colours (VIBGYOR). This experiment demonstrated that white light is made up of seven colours.
Q15. The sequence of colours in the spectrum is remembered as
The sequence of colours in the spectrum is remembered as VIBGYOR: Violet, Indigo, Blue, Green, Yellow, Orange, and Red. This order is from the colour that bends the most (Violet) to the colour that bends the least (Red). VIBGYOR is a common mnemonic used in schools.
Q16. In a glass slab, the emergent ray is laterally
In a glass slab, the emergent ray is laterally displaced (shifted sideways) but remains parallel to the incident ray. This is because the two surfaces of the slab are parallel. The light refracts twice (entering and leaving) and emerges parallel to the incident ray, just shifted to one side.
Q17. The angle between the direction of incident ray and emergent ray is called
The angle between the direction of the incident ray (extended) and the emergent ray is called the angle of deviation. It is the total angle by which light has been bent after passing through a prism. The angle of deviation depends on the prism’s angle and the refractive index of the prism material.
Q18. The colours reach the observer due to
In a rainbow, the colours reach the observer due to internal reflection and dispersion of sunlight inside raindrops. The light enters the raindrop, disperses into colours, reflects off the inner surface of the drop, and then emerges to reach the observer. This combination creates the rainbow.
Q19. A triangular glass prism has how many rectangular lateral surfaces?
A triangular glass prism has three rectangular lateral surfaces. It has two triangular bases (parallel) and three rectangular faces connecting the bases. Light usually passes through two of these rectangular faces—one for entry and one for exit—causing refraction and dispersion.
Q20. The angle between the incident ray and the normal is called
The angle between the incident ray and the normal (an imaginary line perpendicular to the surface at the point of incidence) is called the angle of incidence. It is denoted by the letter ‘i’. This is a basic concept in optics and is used in both reflection and refraction.
Q21. White light consists of
White light consists of seven colours: Violet, Indigo, Blue, Green, Yellow, Orange, and Red (VIBGYOR). This was discovered by Sir Isaac Newton using a prism. When white light is dispersed, these seven colours become visible. The combination of all seven colours in the right proportions creates white light.
Q22. The angle between the two lateral faces of a prism is called
The angle between the two lateral faces (refracting surfaces) of a prism is called the angle of prism (A). It is also known as the refracting angle of the prism. This angle is one of the key factors that determines how much light is deviated when passing through the prism.
Q23. Hot air is
Hot air is less dense than cold air because when air is heated, its molecules move faster and spread out, occupying more volume. This lower density means hot air has a lower refractive index than cold air. This difference in density causes atmospheric refraction, which can make objects appear to waver or mirage.
Q24. The peculiar shape of a prism causes
The peculiar shape of a prism (non-parallel surfaces) causes deviation of light. Unlike a glass slab (which only displaces light), a prism bends light at an angle, causing it to deviate from its original path. This deviation is what allows a prism to disperse white light into its component colours.
Q25. Newton showed that white light is made up of
Newton showed that white light is made up of seven colours. He demonstrated this using a prism, which dispersed white light into a spectrum of seven colours (VIBGYOR). He also showed that these colours could be recombined to form white light using a second prism.
Q26. The apparent position of objects fluctuates due to
The apparent position of objects fluctuates due to refraction in moving (turbulent) air. As hot air rises and moves, the density of air changes, causing light to refract by different amounts. This makes objects appear to shift, waver, or flicker. This is commonly observed above fire or on hot roads.
Q27. The ray inside the prism is called the
The ray inside the prism is called the refracted ray. After the incident ray enters the prism, it bends (refracts) and travels through the prism. This ray inside the prism is the refracted ray. It then hits the second surface and emerges as the emergent ray.
Q28. The angle between refracted ray and the normal is called
The angle between the refracted ray and the normal (at the point of refraction) is called the angle of refraction. It is denoted by the letter ‘r’. This angle is determined by Snell’s law and depends on the refractive indices of the two media and the angle of incidence.
Q29. Which colour bends the most in a prism?
Violet light bends the most in a prism because it has the shortest wavelength among visible colours. Shorter wavelengths travel slower in glass, so they are refracted more. Red light (longest wavelength) bends the least. The order from most to least bending is: Violet > Indigo > Blue > Green > Yellow > Orange > Red.
Q30. The refraction through a prism differs from a glass slab because the emergent ray is
The refraction through a prism differs from a glass slab because the emergent ray is deviated (bent) from its original direction. In a glass slab, the emergent ray is laterally displaced but remains parallel to the incident ray. In a prism, because the surfaces are not parallel, the emergent ray is not parallel to the incident ray.
Q31. Light that gives a spectrum similar to sunlight is called
Light that gives a spectrum similar to sunlight is called white light. Sunlight is white light that contains all seven colours (VIBGYOR). Any light source that produces a continuous spectrum (all colours) is considered white light. Coloured light would give a spectrum with only a specific colour.
Q32. A rainbow can also be seen near
A rainbow can also be seen near a fountain, waterfall, or sprinkler. These sources produce tiny water droplets that can disperse sunlight, creating a rainbow. The same principle applies—the water droplets act as tiny prisms, refracting and dispersing sunlight into colours.
Q33. In a rectangular glass slab, the emergent ray is
In a rectangular glass slab, the emergent ray is parallel to the incident ray but laterally displaced (shifted sideways). This happens because the two surfaces of the slab are parallel. The light refracts twice (entering and leaving) and emerges in the same direction as the incident ray, just shifted.
Q34. The ray coming out of the prism is called the
The ray coming out of the prism is called the emergent ray. It is the light ray that leaves the prism after undergoing refraction. The incident ray enters the prism, the refracted ray travels inside, and the emergent ray exits the prism.
Q35. When a second identical prism is placed inverted, the colours
When a second identical prism is placed inverted (with its base opposite to the first), the colours combine to form white light. The second prism recombines the dispersed colours by bending them back. This experiment, performed by Newton, proved that white light is made up of seven colours.
Q36. Refractive index of hot air is
The refractive index of hot air is less than that of cold air. When air is heated, it expands and becomes less dense. A lower density means a lower refractive index. This difference in refractive index between hot and cold air causes atmospheric refraction, leading to phenomena like mirages.
Q37. The inclined refracting surfaces of a prism cause
The inclined (non-parallel) refracting surfaces of a prism cause both refraction and dispersion. When light enters the prism, it is refracted (bent). Because different colours refract by different amounts, the light is also dispersed into its component colours. This is what makes a prism different from a glass slab.
Q38. Atmospheric refraction occurs due to variation in
Atmospheric refraction occurs due to variation in the density of air. Different layers of the atmosphere have different densities because of differences in temperature and pressure. As light passes through these varying density layers, it bends, causing phenomena like star twinkling and mirages.
Q39. The colours emerge along different paths due to
The colours emerge along different paths due to dispersion. Different colours (wavelengths) have different speeds in glass, so they are refracted by different amounts. This causes them to separate and emerge along different paths. This is why a prism splits white light into a spectrum.
Q40. In rainbow formation, sunlight undergoes
In rainbow formation, sunlight undergoes dispersion and internal reflection inside raindrops. The light enters the drop, disperses into colours, reflects off the inner surface, and then emerges. The combination of dispersion and internal reflection creates the beautiful colours of the rainbow.
Q41. The flickering of objects near fire is an example of
The flickering of objects near a fire is an example of local atmospheric refraction. The hot air near the fire has a different density (and refractive index) than the surrounding cooler air. As light passes through this moving, non-uniform air, it bends and changes, making objects appear to waver or flicker.
Q42. Which colour bends the least in a prism?
Red light bends the least in a prism because it has the longest wavelength among visible colours. Longer wavelengths travel faster in glass, so they are refracted less. Violet light (shortest wavelength) bends the most. The order from least to most bending is: Red < Orange < Yellow < Green < Blue < Indigo < Violet.
Q43. The angle between emergent ray and the normal is called
The angle between the emergent ray and the normal at the point where it leaves the prism is called the angle of emergence. It is denoted by the letter ‘e’. This angle is measured from the normal to the emergent ray.
Q44. A rainbow is seen after
A rainbow is seen after a rain shower because raindrops remain suspended in the atmosphere. These raindrops act as tiny prisms, dispersing sunlight into colours. For a rainbow to form, there must be sunlight shining from behind the observer and raindrops in front.
Q45. When light enters from air to glass, it bends
When light enters from air (rarer medium) to glass (denser medium), it slows down and bends towards the normal. The normal is an imaginary line perpendicular to the surface. The angle of refraction is smaller than the angle of incidence. This is a fundamental law of refraction.
Q46. Atmospheric refraction is caused by Earth’s
Atmospheric refraction is caused by Earth’s atmosphere. Light from celestial objects (like stars and the Sun) passes through different layers of the atmosphere with varying densities. This causes the light to bend (refract), leading to phenomena like twinkling of stars, advance sunrise, and delayed sunset.
Q47. The ray that strikes the prism first is called the
The ray that strikes the prism first is called the incident ray. It is the light ray that enters the prism from the surrounding medium (usually air). It strikes the first refracting surface of the prism and then becomes the refracted ray inside the prism.
Q48. The refraction of light by Earth’s atmosphere is called
The refraction of light by Earth’s atmosphere is called atmospheric refraction. This occurs when light from celestial bodies passes through different layers of the atmosphere with varying densities. It causes phenomena such as twinkling of stars, advance sunrise, delayed sunset, and the apparent flattening of the Sun at sunrise and sunset.
Q49. The splitting of white light into colours is called
The splitting of white light into its constituent colours is called dispersion. This occurs when white light passes through a prism or raindrops. Different colours have different wavelengths and speeds in a medium, so they refract by different amounts and separate into a spectrum (VIBGYOR).
Q50. When light goes from glass to air, it bends
When light goes from glass (denser medium) to air (rarer medium), it speeds up and bends away from the normal. The angle of refraction is larger than the angle of incidence. This is why a pencil in water appears bent—light bends away from the normal as it leaves the water.