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18. If the power of the lens is [tex]-2 D[/tex], its focal length is

a) [tex]-2 m[/tex]

b) [tex]0.5 m[/tex]

c) [tex]-0.55 cm[/tex]

d) [tex]-0.5 m[/tex]



Answer :

GinnyAnswer
To find the focal length of a lens given its power, we can use the formula:

[tex]\[ f = \frac{1}{P} \][/tex]

where:
- [tex]\( f \)[/tex] is the focal length in meters,
- [tex]\( P \)[/tex] is the power of the lens in diopters (D).

Given that the power of the lens [tex]\( P \)[/tex] is [tex]\( -2 \)[/tex] diopters, we can substitute [tex]\( P \)[/tex] into the formula:

[tex]\[ f = \frac{1}{-2} \][/tex]

This simplifies to:

[tex]\[ f = -0.5 \][/tex]

Therefore, the focal length of the lens is [tex]\( -0.5 \)[/tex] meters.

Thus, the correct option is:
d) [tex]\(-0.5 \, \text{m}\)[/tex]

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