• The least distance of distinct vision is about 25cm and the angle of vision is about 600
.
The ability of eye lens to change its focal length is called accommodation of lens.
The defect in which people cannot see objects beyond far point is called Myopia.
The defect in which people cannot see objects situated before near point is called
Hypermetropia.
Presbyopia is a vision defect indicating that the power of accommodation of the eye usually
decreases with ageing.
The reciprocal of focal length is called power of the lens.
The refractive index of prism is given by
n = Sin[(A+D)/2]/Sin(A/2)
where A is angle of prism and D is angle of minimum deviation.
The splitting of white light into colours (VIBGYOR) depending on the wave lengths is called
dispersion.
The process of re-emission of absorbed light in all directions with different intensities by atoms
or molecules, is called scattering of light.
Reflection on concepts
1. How do you correct the eye defect Myopia? (AS1
)
2. Explain the correction of the eye defect Hypermetropia. (AS1
)
3. How do you find experimentally the refractive index of material of a prism? (AS3
)
4. Explain the formation of rainbow. (AS1
)
5. Explain briefly the reason for the blue colour of the sky. (AS1
)
6. Explain two activities for the formation of artificial rainbow. (AS3
)
7. Derive an expression for the refractive index of the material of a prism. (AS1
)
8. Light of wavelength λ1
enters a medium with refractive index n2
from a medium with refractive
index n1
. What is the wave lenght of light in second medium? (AS 1
)
9. Why does the sky sometimes appear white? (AS 7
)
10. A person is viewing an extended object. If a converging lens is placed in front of his eye, will
he feel that the size of object has increased? Why? (AS7
)
Application of Concepts
1) Incident ray on one of the face (AB) of a prism and emergent ray
from the face AC are given in figure -1. Complete the ray
diagram.(AS 5
)
10. A person is viewing an extended object. If a converging lens is placed in front of his eye, will
he feel that the size of object has increased? Why? (AS7
)