Ray Optics And Optical Instruments

(A)
(a) Image distance
Concept: Lens formula
Step 1: Sign convention}
For concave lens: Step 2: Substitute values}
Conclusion (a): (b) Characteristics of image

• Virtual
• Erect
• Diminished
• Formed on the same side as object

(B)
(a) Object distance
Step 1: Sign convention}}
Convex lens: Step 2: Lens formula}}
Step 3: Calculation}}
Conclusion (a): (b) Uses of convex lens in this manner

• Magnifying glass
• Simple microscope

Concept: Addition of Colours (RGB Model)
Primary colours of light: Their combinations produce:

• Red + Blue = Magenta
• Red + Green = Yellow
• Blue + Green = Cyan
• Red + Green + Blue = White

(a) Identify colours A and D
Step 1: From the diagram}
Given:

• One region is marked Red
• One region is Magenta (Red + Blue)
• Center is White (all three)

Step 2: Deduce remaining colours}
Thus: Conclusion (a): (b) Primary colours
Step 1: Primary colours of light}
Step 2: From labels}
Conclusion (b): (c) Complementary colour pair
Concept:
Complementary colours combine to form white light. Step 1: Identify pair}
Step 2: From given labels}
Magenta is present, so: Conclusion (c):

(A) Experiment to explain scattering of light
Concept: Scattering of light (Tyndall effect)
The color of the sky and the Sun is explained by scattering of light by small particles in the atmosphere. Experiment:

• Take a glass tank filled with clean water.
• Add a few drops of milk (to create a colloidal solution).
• Pass a beam of white light (torch or laser) through the solution.

Observation:

• The path of light becomes visible due to scattering.
• Light coming out from the side appears bluish.
• Light observed at the far end appears reddish.

Explanation:

• Shorter wavelengths (blue light) scatter more → sky appears blue.
• At sunrise/sunset, light travels a longer path → blue light scatters away → longer wavelengths (red/orange) dominate.

Conclusion: (B) Scattering of light in atmosphere
(a) Name of the phenomenon
Step 1: Identify phenomenon}
The visible path of light is called: Step 2: Type of medium}
This occurs when light passes through a: Conclusion (a): (b) Intensity of scattering
Step 1: Dependence on wavelength}
Scattering depends on wavelength: Step 2: Other factors}

• Size of particles
• Number of particles
• Nature of medium

Conclusion (b):

Concept: Formation of Rainbow
A rainbow is formed due to the interaction of sunlight with water droplets involving refraction and internal reflection. Step 1: Entry of light into droplet}
When light enters a water droplet:

• It slows down (not increases speed)
• It undergoes refraction

So, statement (i) is incorrect. Step 2: Inside the droplet}
Light reflects inside the droplet:

• This is internal reflection
• In rainbow formation, it is specifically total internal reflection

So, (ii) and (iii) are correct. Step 3: Exit of light}
Light again refracts when exiting the droplet, but the key distinguishing phenomenon is total internal reflection. Step 4: Conclusion}
Correct statements:

Concept: Image formation by a convex lens
A convex lens can form a virtual, erect, and magnified image when the object is placed between the optical centre (O) and the principal focus (F). Step 1: Position of object}
Place the object between: Step 2: Draw principal rays}
From the top of the object:

• Draw a ray parallel to the principal axis; after refraction, it passes through the focus on the other side.
• Draw a ray through the optical centre; it passes undeviated.

Step 3: Extend rays backward}
The refracted rays diverge, so extend them backward. Their extensions meet on the same side of the lens. Step 4: Nature of image}

• Virtual
• Erect
• Magnified
• Formed on the same side of the lens

Ray Diagram: