# Light

## 1 Marks Question

1. Define converging lens.
2. The lens which is thick in the middle and thin at the edge is called a converging lens. It converges the beam of light to a point after the refraction of light.
3. Write the relationship between power of lens and its focal length.
4. The relationship between the power of the lens and its focal length is they are inversely proportional.
5. Where should be object kept in front of the convex lens to get magnification 1?
6. In front of the convex lens, the object should be kept at 2F to get a magnification of 1.
7. What is power of lens?
8. The power of a lens is its ability to converge or diverge the incident beam of light. Its unit is a diopter (D).
9. Write the formula of power lens.
10. The formula of power lens is:
power = $\frac{1}{\text{focal length}}$
11. Write the formula of power and magnification of lens.
12. The formula to calculate power(p) and magnification(m) of lens is:

p = $\frac{1}{\text{focal length}}$
m = $\frac{\text{size of image (I)}}{\text{size of object (O)}}$ = $\frac{\text{height of image (v)}}{\text{height of object (u)}}$

13. What is the near point of a normal eye?
14. The near point of a normal eye is 25 cm.
Definition: It is minimum distance for the eye beyond which an eye can accommodate and focus object clearly.
15. What is the unit of magnification?
16. Magnification has no unit.
17. What is focal length?
18. The distance between the optical center and the principal focus of a lens is called its focal length.
19. What is magnification of lens?
20. When the object comes near the lens its image becomes larger and vice-versa. This property of the lens is magnification.

Similarly, magnification of a lens is defined as ratio of size of the image to the size of the object.

magnification = $\frac{\text{size of image (I)}}{\text{size of object (O)}}$
21. What is long-sightedness?
22. The defect of vision in which a person can see distant object but cannot see nearby object is called long-sightedness (hypermetropia).
More info: The defect of vision in which a person cannot see distant object but can see nearby object is called short-sightedness (myopia).
23. The magnification is less than one, what does it mean?
24. The magnification is less than one, which means that the size of the image is smaller than the size of the object. In this case, the image is said to be diminished.
Info: If M = 1, the size of image is equal to the size of object, If M > 1, the size of image will be larger than the size of object. In this case, the image is said to be magnified.
25. What formula is used to find the fluctuation of the shape of a body?
26. The formula which is used to find the fluctuation of the shape of a body is: sin i/ sin r.
27. What is optical center?
28. The geometrical center of a lens is called the optical center.
29. What is far point?
30. The farthest point from the eye at which an object can be seen clearly by the eye is called the far point of the eye. For a normal eye, the far point is at infinity.
31. What is the meaning of the saying, "the power of a lens is 1 diopter"?
32. The meaning of the saying, "the power of a lens is 1 diopter" is that the lens/mirror has a focal length of 1 meter.
33. What is meant by defects of vision?
34. The eye which can’t see objects placed at a short distance or a long distance is said to have a defect of vision.