JEE Physics

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Chapter 35

Experiment - Focal Length Of (I) Convex Mirror (Ii) Concave Mirror (Iii) Convex Lens - all with Video Answers

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Chapter Questions

Problem 2879

A concave lens of focal length $\mathrm{f}$ forms an image which is n times the size of the object. What is the distance of the object from the lens?
(A) $(1+\mathrm{n}) \mathrm{f}$
(B) $(1-\mathrm{n}) \mathrm{f}$
(C) $[(1-\mathrm{n}) / \mathrm{n}] \mathrm{f}$
(D) $[(1+\mathrm{n}) / \mathrm{n}] \mathrm{f}$

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Problem 2880

A convex lens of focal length $\mathrm{f}$ is placed somewhere in between an object and a screen. The distance between the object and the screen is $\mathrm{x}$. If the numerical value of the magnification product by the lens is $\mathrm{m}$, What is the focal length of the lens?
(A) $\left[\mathrm{mx} /(\mathrm{m}-1)^{2}\right]$
(B) $\left[\mathrm{mx} /(\mathrm{m}+1)^{2}\right]$
(C) $\left[(m-1)^{2} / \mathrm{m}\right] \mathrm{x}$
(D) $\left[(\mathrm{m}+1)^{2} / \mathrm{m}\right] \mathrm{x}$

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Problem 2881

A convex lens of focal length $f$ produces a real image $x$ times the size of an object, Then what is the distance of the object from the lens?
(A) $(\mathrm{x}+1) \mathrm{f}$
(B) $(\mathrm{x}-1) \mathrm{f}$
(C) $[(\mathrm{x}+1) / \mathrm{x}] \mathrm{f}$
(D) $[(x-1) / x] f$

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Problem 2882

A thin lens has focal length $\mathrm{f}$, and its aperture has diameter
d. It forms an image of intensity I. Now, the central part of the aperture upto diameter $(\mathrm{d} / 2)$ is blocked by an opaque paper. The focal length and image intensity will change to $\ldots$
(A) $\mathrm{f}$ and $(3 \mathrm{I} / 4)$
(B) $(3 \mathrm{f} / 4)$ and $(\mathrm{I} / 2)$
(C) $\mathrm{f}$ and $(\mathrm{I} / 4)$
(D) $(\mathrm{f} / 2)$ and $(\mathrm{I} / 2)$

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Problem 2883

The distance between object and the screen is D. Real images of an object are formed on the screen two positions of a lens separated by a distance $\mathrm{d}$. What will be the ratio between the sizes of two images?
(A) $\left(\mathrm{D}^{2} / \mathrm{d}^{2}\right)$
(B) $(\mathrm{D} / \mathrm{d})$
(C) $\sqrt{(\mathrm{D} / \mathrm{d})}$
(D) $\left[(\mathrm{D}-\mathrm{d})^{2} /(\mathrm{D}+\mathrm{d})^{2}\right]$

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Problem 2884

A spherical mirror forms an erect image three times the linear size of the object. If the distance between the object and the image is $80 \mathrm{~cm}$, What is the focal length of the mirror?
(A) $30 \mathrm{~cm}$
(B) $40 \mathrm{~cm}$
(C) $-15 \mathrm{~cm}$
(D) $15 \mathrm{~cm}$

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Problem 2885

Which of the following graphs is the magnifications of a real image against the distance from the focus of a concave mirror ?

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Problem 2886

A short linear object of length $L$ lies on the axis of a spherical mirror of focal length of $f$ at a distance $u$ from the mirror. Its image has an axial length $L^{\prime}$ equal to $\ldots \ldots \ldots$..
(A) $\mathrm{L}[\mathrm{f} /(\mathrm{u}-\mathrm{f})]^{2}$
(B) $\mathrm{L}[(\mathrm{u}-\mathrm{f}) / \mathrm{f}]^{2}$
(C) $\mathrm{L}[(\mathrm{u}+\mathrm{f}) / \mathrm{f}]^{1 / 2}$
(D) $L[f /(u-f)]^{1 / 2}$

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Problem 2887

A concave mirror of focal length $\mathrm{f}$ produces an images n times the size of the object. If the image is real then What is the distance of the object from the mirror?
(A) $(\mathrm{n}+1) \mathrm{f}$
(B) $[(\mathrm{n}-1) / \mathrm{n}] \mathrm{f}$
(C) $(\mathrm{n}-1) \mathrm{f}$
(D) $[(\mathrm{n}+1) / \mathrm{n}] \mathrm{f}$

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Problem 2888

An object is placed at a distance of $(\mathrm{f} / 2)$ the from a convex lens the image will be....
(A) at $\mathrm{f}$, real and inverted
(B) at,$(3 \mathrm{f} / 2)$ real and inverted
(C) at one of the foci, virtual and double its size
(D) at $2 \mathrm{f}$, virtual and erect.

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