General Q&A for Class 12 · Page 167
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
What is called refractive index?
Refractive index, also known as the index of refraction, is the optical property that quantifies how light behaves when entering a transparent material. It's called "refractive" because it relates to refraction—the phenomenon where light changes direction at the boundary between two different media. This fundamental property helps us understand everything from why a straw appears bent in water to how lenses in eyeglasses and cameras focus light.
- GeneralClass 12All
What is another name for the refractive index?
The refractive index is also commonly called the "index of refraction" or simply abbreviated as "RI" or "n" in scientific notation. In technical literature, you might also encounter terms like "optical density" when comparing materials, though this isn't exactly synonymous.
- GeneralClass 12All
What is the formula for the refractive index?
The primary formula for refractive index is: n = c/v Where: n = refractive index c = speed of light in vacuum (approximately 3 × 10⁸ m/s) v = speed of light in the medium
- GeneralClass 12All
What are the two formulas of refractive index?
The two main formulas for calculating refractive index are: Speed-based formula: n = c/v (ratio of light speed in vacuum to light speed in the medium) Snell's Law formula: n₁ sin θ₁ = n₂ sin θ₂, which can be rearranged to find the relative refractive index: n₂₁ = n₂/n₁ = sin θ₁/sin θ₂ For a single medium relative to air/vacuum: n = sin i/sin r (where i is the angle of incidence and r is the angl
- GeneralClass 12All
How to find v from i and r?
To find the speed of light (v) in a medium using angles of incidence (i) and refraction (r): First, calculate the refractive index: n = sin i/sin r Then use the formula: v = c/n For example, if light enters water at 45° (i) and refracts to 32° (r): n = sin 45°/sin 32° = 0.707/0.530 ≈ 1.33 v = (3 × 10⁸ m/s)/1.33 ≈ 2.25 × 10⁸ m/s
- GeneralClass 12All
How to find v with c and n?
This is straightforward using the basic refractive index formula rearranged: v = c/n Simply divide the speed of light in vacuum (c = 3 × 10⁸ m/s) by the refractive index (n) of the material. For instance, if glass has n = 1.5, then v = 3 × 10⁸/1.5 = 2 × 10⁸ m/s.
- GeneralClass 12All
How to find sin i and sin r?
To find sin i (sine of angle of incidence) and sin r (sine of angle of refraction): Measure the angles using a protractor or calculation from experimental data Use a calculator or trigonometric tables to find the sine values Alternatively, if you know the refractive indices, use Snell's law: n₁ sin i = n₂ sin r For example, if light travels from air (n=1) to water (n=1.33) at 30° incidence: sin i = sin 30° = 0.5 <
- GeneralClass 12All
What is sin I in Snell's law?
In Snell's law, "sin i" (or sin I) represents the sine of the angle of incidence—the angle at which light strikes the interface between two media, measured from the perpendicular (normal) to the surface. This is a crucial component because it determines how much the light will bend when entering a new medium.
- GeneralClass 12All
How to calculate the refractive index of light?
To calculate the refractive index experimentally: Using angles: Measure the angle of incidence (i) and angle of refraction (r), then calculate n = sin i/sin r Using speed: Measure the speed of light in the medium (v), then calculate n = c/v Using wavelength: Measure wavelengths in vacuum (λ₀) and in the medium (λ), then calculate n = λ₀/λ The most common classroom
- GeneralClass 12All
How to calculate sin law?
To apply the sine law (Snell's law) in calculations: Identify the two media and their refractive indices (n₁ and n₂) Measure or identify the angle of incidence (θ₁) Apply the formula: n₁ sin θ₁ = n₂ sin θ₂ Rearrange to find the unknown: sin θ₂ = (n₁ sin θ₁)/n₂ Calculate θ₂ = arcsin[(n₁ sin θ₁)/n₂]
- GeneralClass 12All
What is the refractive index?
The refractive index (RI) is a dimensionless number that describes how light propagates through a medium. It measures how much light bends (refracts) when passing from one material to another. Specifically, it represents the ratio of the speed of light in a vacuum to its speed in a given material. A higher refractive index indicates that light travels more slowly through that substance, causing greater bending of light rays.
- GeneralClass 12All
How do you calculate speed, distance, and time?
To calculate these values, identify which two quantities you know and use the appropriate formula: For Speed: Divide the distance traveled by the time taken. If you travel 150 km in 3 hours, your speed is 150 ÷ 3 = 50 km/h. For Distance: Multiply speed by time. If you drive at 80 km/h for 4 hours, you cover 80 × 4 = 320 km. For Time: Divide distance by speed. To travel 200 km at 50 km/h takes 200 ÷
- GeneralClass 12All
Is speed represented by U or V in physics?
In physics, speed and velocity are typically represented by the letter V, not U. The letter U is often used to represent initial velocity in equations of motion, while V represents final velocity or general velocity. Speed specifically refers to how fast an object moves regardless of direction, while velocity includes directional information.
- GeneralClass 12All
What is the speed of 100 km in 1 hour?
The speed is 100 km/h (kilometers per hour). This is calculated by dividing distance by time: 100 km ÷ 1 hour = 100 km/h. This represents a steady highway cruising speed for most vehicles.
- GeneralClass 12All
What is the speed of 60 km in 1 hour?
The speed is 60 km/h. Using the formula Speed = Distance ÷ Time, we get 60 km ÷ 1 hour = 60 km/h. This is a common urban speed limit in many countries
- GeneralClass 12All
What is the speed of 5 km in 30 minutes?
. The speed is 10 km/h. First, convert 30 minutes to hours (30 ÷ 60 = 0.5 hours), then calculate: 5 km ÷ 0.5 hours = 10 km/h. This is approximately the speed of a brisk walk or slow jog.
- GeneralClass 12All
What is the speed of 1.5 km in 5 minutes?
The speed is 18 km/h. Convert 5 minutes to hours (5 ÷ 60 = 0.0833 hours), then calculate: 1.5 km ÷ 0.0833 = 18 km/h. This represents a moderate running pace.
- GeneralClass 12All
When a car travels a distance of 500 km in 10 hours, what is the speed?
The average speed is 50 km/h. Using Speed = Distance ÷ Time: 500 km ÷ 10 hours = 50 km/h. This accounts for the entire journey including any stops or slowdowns.
- GeneralClass 12All
If a car travels 240 km in 4 hours, what is the speed?
The average speed is 60 km/h. Calculate by dividing: 240 km ÷ 4 hours = 60 km/h. This represents a reasonable average for mixed driving conditions.
- GeneralClass 12All
What speed is 3×10⁸ or what is c = 3×10⁸ m/s?
This represents the speed of light in a vacuum, which is approximately 300,000,000 meters per second (or 300,000 km/s). In scientific notation, this is written as 3×10⁸ m/s. The letter 'c' is the universal symbol for the speed of light, which is the fastest speed possible in the universe according to Einstein's theory of relativity.