To solve the problem, we need to identify the defect that causes people to have difficulty seeing near objects clearly, but allows them to see distant objects clearly.
1. Understanding the Defects:
- Myopia (or nearsightedness) is a condition where people can see near objects clearly, but distant objects appear blurred. This is the opposite of the given condition.
- Cataract is a condition where the eye's lens becomes cloudy, affecting vision at all distances.
- Presbyopia is a condition associated with aging, where the ability to focus on near objects decreases, but distant vision may remain clear.
- Hypermetropia (or farsightedness) is the defect where people can see distant objects clearly, but near objects appear blurred. This matches the condition described in the question.
Final Answer:
The defect described is called Hypermetropia (Option D).
Two light beams fall on a transparent material block at point 1 and 2 with angle \( \theta_1 \) and \( \theta_2 \), respectively, as shown in the figure. After refraction, the beams intersect at point 3 which is exactly on the interface at the other end of the block. Given: the distance between 1 and 2, \( d = 4/3 \) cm and \( \theta_1 = \theta_2 = \cos^{-1} \frac{n_2}{2n_1} \), where \( n_2 \) is the refractive index of the block and \( n_1 \) is the refractive index of the outside medium, then the thickness of the block is cm. 