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Q1. Which three lie in the same plane according to first law of refraction?
The first law of refraction states that the incident ray, the refracted ray, and the normal at the point of incidence all lie in the same plane. This is similar to the law of reflection and is a fundamental principle of optics.
Q2. The constant ratio in refraction law is between
According to Snell’s law, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media. This constant is called the refractive index.
Q3. The law relating sine of angles is called
Snell’s law states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media. It is named after the Dutch mathematician Willebrord Snellius.
Q4. Refractive index is defined as
Refractive index is the ratio of the speed of light in a vacuum (or air) to the speed of light in a given medium. It tells us how much light slows down when it enters a medium. A higher refractive index means light travels slower in that medium.
Q5. Symbol used for refractive index of medium 2 relative to medium 1 is
The refractive index of medium 2 with respect to medium 1 is written as n21. The first subscript (2) is the medium the light is entering, and the second subscript (1) is the medium it is coming from. So n21 means “from medium 1 to medium 2.”
Q6. Refractive index represents change in
Refractive index is a measure of how much the speed of light changes when it enters a medium from a vacuum (or air). It does not directly measure the bending angle, though bending is a consequence of the speed change.
Q7. Light travels fastest in
Light travels fastest in a vacuum, where its speed is approximately 3 × 10⁸ m/s. In any material medium like water, glass, or oil, light slows down. Vacuum has the lowest refractive index (1.00), meaning no slowing of light.
Q8. Speed of light in vacuum is
The speed of light in a vacuum is approximately 3 × 10⁸ meters per second (more precisely, 299,792,458 m/s). This is the fastest speed at which light can travel and is a fundamental constant in physics.
Q9. Speed of light in air compared to vacuum is
The speed of light in air is slightly less than in a vacuum. However, the difference is very small, so for most practical calculations, the speed of light in air is taken as approximately equal to the speed in a vacuum (3 × 10⁸ m/s). The refractive index of air is about 1.0003.
Q10. Speed of light in water is
Light travels considerably slower in water than in a vacuum. The speed of light in water is about 2.25 × 10⁸ m/s, which is roughly 75% of its speed in a vacuum. This is why the refractive index of water is 1.33.
Q11. If light goes from medium 1 to 2, refractive index is
The refractive index of medium 2 with respect to medium 1 (n21) is given by the ratio of the speed of light in medium 1 (v1) to the speed of light in medium 2 (v2). So, n21 = v1/v2. If medium 2 is denser, this value is greater than 1.
Q12. Refractive index depends on
Refractive index depends on the speed of light in a medium. It also depends on the wavelength (color) of light and the temperature of the medium. However, it does not depend on the shape or size of the medium.
Q13. Angle of incidence is represented by
The angle of incidence is the angle between the incident ray and the normal at the point of incidence. It is denoted by the letter ‘i’. The angle of refraction is denoted by ‘r’, and refractive index is denoted by ‘n’.
Q14. Angle of refraction is denoted by
The angle of refraction is the angle between the refracted ray and the normal at the point of incidence. It is denoted by the letter ‘r’. The angle of incidence is denoted by ‘i’, and the refractive index is denoted by ‘n’.
Q15. Refractive index of water is
The refractive index of water is approximately 1.33. This means that light travels 1.33 times slower in water than in a vacuum. This is why objects appear bent when seen through water (like a straw in a glass of water).
Q16. Refractive index indicates
Refractive index is a measure of the optical density of a medium. A higher refractive index means the medium is optically denser and light travels slower in it. It is not the same as mass density (mass per unit volume), though they are often related.
Q17. When light enters another medium obliquely, it
When light enters another medium at an angle (obliquely), it changes direction or bends. This bending of light is called refraction. If light enters along the normal (perpendicular), it does not bend and continues straight.
Q18. Refractive index of medium 1 w.r.t 2 is
The refractive index of medium 1 with respect to medium 2 is written as n12. The first subscript (1) is the medium being entered, and the second (2) is the medium being left. So n12 means “from medium 2 to medium 1.”
Q19. Absolute refractive index is taken with respect to
Absolute refractive index is the refractive index of a medium with respect to a vacuum (or air, for practical purposes). It compares the speed of light in a vacuum to the speed of light in that medium. So, absolute refractive index n = c/v.
Q20. Symbol for absolute refractive index is
Absolute refractive index is commonly denoted by the symbol ‘n’ or ‘nm’ (n for medium). It does not have subscripts because it is always measured with respect to vacuum or air. For example, n for water is 1.33, and n for glass is about 1.50.
Q21. Formula for absolute refractive index is
The absolute refractive index (n) is the ratio of the speed of light in a vacuum (c) to the speed of light in the medium (v). So, n = c/v. Since c is constant and v is always less than c, the refractive index is always greater than or equal to 1.
Q22. Refraction occurs due to change in
Refraction occurs because light changes speed when it enters a different medium. This change in speed causes a change in direction (bending) when light enters at an angle. So both speed and direction change during refraction.
Q23. Refractive index is a
Refractive index is a scalar quantity, meaning it has only magnitude and no direction. It is simply a number (like 1.33 for water) that compares the speed of light in two media. It does not have a direction like force or velocity.
Q24. Snell’s law is valid for
Snell’s law is valid for a given color (wavelength) of light and a given pair of media. Different colors have different refractive indices in the same medium (dispersion). So, Snell’s law applies specifically to each color separately.
Q25. Refractive index changes when
Refractive index is a property of a medium. It changes when the medium changes (e.g., from air to water). It also changes with the color (wavelength) of light and temperature, but it does not depend on the angle of incidence or the thickness of the medium.
Q26. Normal is drawn
The normal is an imaginary line drawn perpendicular (at 90°) to the surface at the point where the light ray strikes. All angles in refraction (angle of incidence and angle of refraction) are measured with respect to this normal line.
Q27. No refraction when incidence is
When light strikes a surface at normal incidence (perpendicular, i = 0°), it does not bend and continues straight. There is no refraction because the light does not change direction, even though its speed changes. Refraction only occurs when light enters at an oblique angle.
Q28. sin i / sin r is
According to Snell’s law, the ratio of sin i (angle of incidence) to sin r (angle of refraction) is a constant for a given pair of media. This constant is the refractive index (n). So, sin i / sin r = n (constant).
Q29. Refraction proves light changes
Refraction is direct evidence that the speed of light changes when it enters a different medium. The bending of light is a result of this speed change. This was a major discovery that helped scientists understand the nature of light.
Q30. Higher refractive index indicates
A higher refractive index means that light travels slower in that medium. Since n = c/v, if n is high, v (speed in the medium) must be low. For example, diamond has a high refractive index (n = 2.42), so light travels very slowly in it.
Q31. When light slows, refractive index
Refractive index is inversely proportional to the speed of light in a medium. When light slows down (speed decreases), the refractive index increases. So, a slower speed means a higher refractive index.
Q32. Refraction happens at
Refraction occurs at the boundary (interface) between two transparent media. When light crosses this boundary, its speed changes, causing it to bend. The boundary is the surface where the two media meet, like the surface of water or glass.
Q33. Refractive index of vacuum is
The refractive index of a vacuum is exactly 1. This is because light travels at its maximum speed in a vacuum (c), and n = c/v. Since v = c in vacuum, n = 1. Air has a refractive index very close to 1 (approximately 1.0003).
Q34. Glass has higher refractive index than
Glass has a higher refractive index (about 1.50) than air (about 1.00). However, diamond (2.42) has a higher refractive index than glass, and water (1.33) has a lower refractive index than glass. So among the options, glass is higher than air only.
Q35. Snell’s law relates
Snell’s law relates the sines of the angles of incidence and refraction. The law states: sin i / sin r = n (constant). It does not directly relate the angles themselves, but the sines of the angles.
Q36. Refraction occurs in
Refraction occurs only in transparent media like glass, water, air, and clear plastics. These media allow light to pass through. Mirrors reflect light, metals block or reflect light, and in vacuum, there is no medium to cause refraction.
Q37. Maximum slowing of light occurs in
Among the given options, glass slows light the most. The speed of light in glass is about 2 × 10⁸ m/s (n ≈ 1.50), compared to water (2.25 × 10⁸ m/s, n ≈ 1.33) and air (almost 3 × 10⁸ m/s). Vacuum does not slow light at all.
Q38. Symbol for refractive index
The standard symbol for refractive index is ‘n’. It comes from the Latin word “index” and is used worldwide in physics. Other symbols like f (focal length), m (magnification), and R (radius of curvature) are used for different quantities.
Q39. Refractive index increases when speed
Refractive index is inversely proportional to the speed of light in a medium. So, when the speed of light decreases (light slows down), the refractive index increases. This is why denser media have higher refractive indices.
Q40. Refractive index depends on color because of
Different colors (wavelengths) of light travel at different speeds in the same medium, so they have different refractive indices. This phenomenon is called dispersion. It is why a prism splits white light into its constituent colors (rainbow effect).
Q41. Law of refraction states ratio is constant for
The ratio sin i / sin r is constant for a given color (wavelength) of light and a given pair of media. Different colors have different refractive indices, which is why dispersion occurs. So the law applies specifically to each color separately.
Q42. Refractive index compares speed in
Refractive index is always a comparison of the speed of light in two media. Absolute refractive index compares a medium with vacuum (or air), while relative refractive index compares two different media (e.g., water with glass).
Q43. If medium 2 is denser, refracted ray bends
When light travels from a rarer medium (like air) to a denser medium (like glass or water), it slows down and bends towards the normal. This means the angle of refraction (r) is less than the angle of incidence (i).
Q44. Absolute refractive index compares medium with
Absolute refractive index is the refractive index of a medium compared to a vacuum (or air for practical purposes). It is given by n = c/v, where c is the speed of light in a vacuum and v is the speed in the medium.
Q45. Refractive index unit is
Refractive index is a dimensionless quantity, meaning it has no unit. It is simply a ratio of two speeds (c/v) or the ratio of two sines (sin i / sin r). Both the numerator and denominator have the same units, so they cancel out.
Q46. Smaller wavelength means
In a medium, shorter wavelengths (like violet or blue light) have a higher refractive index and bend more. Longer wavelengths (like red light) have a lower refractive index and bend less. This is why dispersion occurs in a prism.
Q47. Light entering denser medium becomes
When light enters a denser medium (like air to glass), its speed decreases because the denser medium has a higher refractive index. This slowing down is what causes the light to bend towards the normal.
Q48. Refraction shows light does not travel
Refraction shows that light does not travel at the same speed in all media. It travels fastest in a vacuum and slows down in material media like water and glass. This difference in speed is the reason for refraction.
Q49. Medium with lowest refractive index is
Among the given options, air has the lowest refractive index (approximately 1.0003). Water has n ≈ 1.33, glass has n ≈ 1.50, and diamond has the highest n ≈ 2.42. Lower refractive index means light travels faster.
Q50. Highest refractive index among given is
Diamond has the highest refractive index among the given options, with n ≈ 2.42. This high refractive index is why diamonds sparkle so much—they bend light significantly and cause total internal reflection, giving them their characteristic brilliance.