1. Defects of eye and phenomenon of light

The chapter on human eye and the colourful world is assigned a weightage of \(3\ or\ 4\) marks, highlighting its significance in the overall curriculum. 

 

prepare effectively for related exam questions. It is essential to grasp the concepts of parts and functions of the human eye, defects of vision and their correction, atmospheric refraction, dispersion, and scattering of light. Focusing on these concepts will greatly benefit both academic performance and practical application in physics.

 

Below, we have provided the details of the question distribution among the different sections.

• Understanding eye structure:  Describe the structure and function of the human eye, including its key parts like the cornea, lens, retina, and optic nerve.
• Identify the defects of vision: Detect the defects in the human eye (myopia, hypermetropia, presbyopia) and their causes in order to devise a correction method for them.
• Analyse the refraction of light through a prism: Examine the path of light rays through a prism how the light gets deviated when traveling through a prism.
• Colour perception: Understand how colours are perceived through the combination of different wavelengths of light.
• Visual phenomena:  Explain various visual phenomena, such as the formation of rainbows and the appearance of the colour of the sky

 

 

Glass slab does not deviate, nor does it disperse the light rays whenever passing through it. This suggests that the incident and the emergent ray emerging from the glass slab are parallel. The glass slab only creates a lateral or sideways shift or displacement to the direction of light.

 

The refraction happens only at the boundary. Once the light has passed the boundary between the two media, it travels in a straight line.

 

The peculiar shape of the prism makes the emergent ray bend at an angle to the direction of the incident ray. This angle is called the angle of deviation.

 

 

 

Different colours deviate by different amounts due to different wavelengths.

 

• Turn the prism slowly until the light that comes out of it appears on a nearby screen.
• You will find a beautiful band of colours.
• The prism has probably split the white incident light into a band of colours.
• Observe the colours that appear at the two extremes of the colour band.
• The different colours seen are Violet, Indigo, Blue, Green, Yellow, Orange and Red, as shown in the figure.

 

 

The twinkling of a star is because of the atmospheric refraction of starlight. On entering the earth's atmosphere, the starlight experiences refraction continuously before it reaches the Earth. The atmospheric refraction happens in a medium of continuously changing refractive index. Since the starlight is bent by the atmosphere towards the normal, its apparent position is slightly different from its actual position. 

 

 

Rainbow formation - Refraction, dispersion, total internal reflection.

 

 

 

The sun is rising above the horizon during sunrise. The rays from the sun refract as they move from denser (more dense) air to lighter air. Also, the human eye can see the sun rays as a straight line, which appears as the sun has risen. But it has actually not yet risen.