CBSE Class 10 Science 2019 · Paper 31/4/1 · Question 24(a)

Light - Reflection and Refraction 2 marks Medium

Study the following ray diagram and list two mistakes committed by the student while tracing it. Rectify these mistakes by drawing the correct ray diagram to show the real position and size of the image corresponding to the position of the object AB.

Answer

The foci were unequally spaced and the image misplaced; correctly, the image is real, inverted, magnified and beyond $2 F_{2}$ .

Mistakes (any two): (1)

F_{1}

and

F_{2}

are not marked at equal distances from the optical centre:

O F_{1} \neq = O F_{2}

(and likewise

O 2 F_{1} \neq = O 2 F_{2}

), although the two foci of a lens are equidistant from O. (2) The image is shown between

F_{2}

and

2 F_{2}

; for an object placed between

F_{1}

and

2 F_{1}

the image must be formed beyond

2 F_{2}

. (3) The image should be magnified; the image drawn is only slightly larger than AB. Correct ray diagram (see the figure): with

F_{1}

F_{2}

equidistant from O and

2 F_{1}

2 F_{2}

at twice that distance, the ray from A parallel to the axis passes through

F_{2}

after refraction and the ray through O goes undeviated. They meet beyond

2 F_{2}

, giving a real, inverted and magnified image A′B′ (for example,

u = - 1.5 f

gives

v = + 3 f

and

m = - 2

🔒 Step-by-step solution

CBSE Class 10 Science 2019 · Paper 31/4/1 · Question 24(a)

Answer

From the board papers

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