Question

if a person in the previous problem uses spectacles of power plus 1 dioptre what is the distance. For him near. 75cm

Answer 1

Answer:

Here we have:-

P=+1 diopter.

and as we know:-

1/f=P

f=1/1 meter

f=1 meter

now we have,

u= infinite, v=? and f= 1m

using lens formula:-

1/f=1/v-1/u

1/1=1/v. ------[since u is infinite, we will ignore it]

v=1m

v=100cm.

so, the right answer is 100cm and surprisingly it isn't in any option.

Thank you.. :-)

Explanation:

Answer 2

Answer:

Near point = 75cm and

Power of lens = +1D

P = 100/f (in cm)

f = 100/P

= 100/1

= 100 cm

The distant of distinct vision v can be found as below.

Using lens formula here:

1/f = 1/v - 1/u

1/v = 1/f + 1/u

= 1/100 + 1/-75 = 3-4/300

= -1/300

= -300 cm

= -3 m ( in metres )

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