A person can see clearly objects only when they lie between 50 cm and 400 cm from his eyes. In order to increase the maximum distance of distinct vision to infinity, the type and power of the correcting lens, the person has to use will be:

A man with hypermetropia cannot see objects closer than a distance of \(40~\text{cm}\) from the eye. The power of the lens required so that he can see objects at \(25~\text{cm}\) from the eye is:
1. \(+4.5~\text{D}\)
2. \(+4.0~\text{D}\)
3. \(+1.5~\text{D}\)
4. \(+3.0~\text{D}\)

The near point of a person is 50 cm and the far point is 1.5 m. The spectacles required for reading purposes and for seeing distant objects are respectively:

1. + 2D, \(-\frac{2}{3}~D\)
2. \(+\frac{2}{3}~D\), - 2 D

3. - 2 D, \(+\frac{2}{3}~D\)

4. \(-\frac{2}{3}~D\), + 2 D

A boy with defective eye-sight cannot see things beyond 50 cm. The corrective lens required has the power:

1. +1 D

2. +2 D

3. -1 D

4. -2 D

A person can see objects clearly between 1 m and 3 m. The power of lens required to correct near point will be:

1.  $-$2.5 D

2.  + 3 D

3.  + 1.5 D

4.  $-$1.75 D

If there had been one eye of a man, then:

The diameter of the eye-ball of a normal eye is about 2.5 cm. The power of the eye lens varies from:

1. 2 D to 10 D

2. 40 D to 32 D

3. 9 D to 8 D 

4. 44 D to 40 D