Light Energy — Important Questions

Concave lens

Step 1: Understand myopia - the eye cannot see distant objects clearly because images form before the retina. Step 2: In myopia, the eye lens is too converging or the eyeball is too long. Step 3: A concave lens is diverging, which spreads out light rays before they enter the eye. Step 4: This diverging action ensures that when the eye lens converges the light, the image forms exactly on the retina. Step 5: This is why people with myopia wear glasses with negative power (concave lenses) to see distant objects clearly.

Dispersion

Step 1: Understand that white light contains all colors of the spectrum (VIBGYOR). Step 2: Different colors have different wavelengths and thus different refractive indices in the same medium. Step 3: When white light enters a prism, each color bends by a different amount due to different refractive indices. Step 4: This separation of white light into its constituent colors is called dispersion. Step 5: Rainbow formation is a natural example of dispersion when sunlight passes through water droplets in the atmosphere.

1.5

Step 1: Recall that refractive index n = speed of light in vacuum / speed of light in medium. Step 2: Speed of light in vacuum c = 3 × 10⁸ m/s (standard value). Step 3: Speed of light in the medium v = 2 × 10⁸ m/s (given). Step 4: Calculate n = (3 × 10⁸) / (2 × 10⁸) = 3/2 = 1.5. Step 5: This means light travels 1.5 times slower in this medium compared to vacuum, indicating it's denser than air.

Convex mirror

Step 1: Understand the requirements for a rear-view mirror - it should provide a wide field of view to see more area behind the vehicle. Step 2: Convex mirrors always form virtual, erect, and diminished images regardless of object position. Step 3: The diminished images allow more objects to fit in the mirror's field of view. Step 4: This gives drivers a wider view of the road behind them, improving safety. Step 5: The warning 'Objects in mirror are closer than they appear' is because convex mirrors make things look smaller and farther than reality.