Question 1
Question: Name any two defects of eye?
Answer: Myopia and hypermetropia are the most common defects of eye.
Question 2
Question: Define power.
Answer: The power of a lens is defined as the reciprocal of its focal length in metres.
Question 3
Question: What is least distance of distinct vision?
Answer: The minimum distance upto which an eye can see clearly is called the least distance of distinct vision.
Question 4
Question: Name the defect of vision in which the eye ball becomes small.
Answer: The defect of vision in which the eyeball becomes small is hypermetropia.
Question 5
Question: Explain what is the power of accommodation of an eye.
Answer: The ability of the eye lens to change its focal length to focus the images of all the objects, distant or nearby on the retina is known as the power of accommodation. The eye lens changes its focal length by changing its thickness with the help of its ciliary muscles.
Question 6
Question: With the help of a ray diagram explain hypermetropia.
Answer: Hypermetropia is the defect of the eye due to which the eye is not able to see clearly the nearby objects though it can see the distant objects clearly.
Question 7
Question: What causes myopia?
Answer: Myopia is caused due to the
1) Shortening of the eyeball
2) Increase in focal length of the eye-lens.
Question 8
Question: What is astigmatism? How is it rectified?
Answer: Astigmatism is one of the defects of the vision. Here the eye is not able to focus the light coming from the horizontal and vertical planes simultaneously. It is rectified by using cylindrical lens.
Question 9
Question: Define dispersion.
Answer: The phenomenon by which, a ray of light splits into its constituent colours, when passed through a transparent medium, is known as dispersion.
Question 10
Question: Name any one source of polychromatic light.
Answer: The sun gives out white light. It is the largest source of polychromatic light.
