The figure is a scaled diagram of a an object and a converging lens. The focal l

Question

The figure is a scaled diagram of a an object and a converging lens. The focal length of the lens is 5.0 units. An object is placed 3.0 units from the lens as shown. 17.. Approximately, what is the image distance? A) -2.0 units B) -4.0 units C) +6.0 units D) -7.5 units E) +9.0 units Ans: D Refer To: Ref 26-8 Difficulty: Medium SectionDef: Section 26-6, 26-7, 26-8 18. The object has a height of 1.5 units. What is the approximate height of the image? A) 2.0 units B) 1.2 units C) 5.0 units D) 3.8 units E) 9.8 units Ans: D Refer To: Ref 26-8 Difficulty: Medium SectionDef: Section 26-6, 26-7, 26-8

Explanation / Answer

17)

by using lens formula

1/u+1/v=1/f

here,

object distance u=3 units

focal length f=5 units

image distance is v

now,

1/3 +1/v=1/5

===>

v=-7.5 units

here, image is virtual,erected and magnified and formed on the same side of object

so option (D) is correct

18)

let

object height h=1.5 units,

image height is h',

then

magnification m=h'/h=v/u

h'= h*(v/u)

= 1.5*7.5/3

= 3.75 units

or

h'=3.8 units (approximatly)

hence option (D) is correct

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