A screen is placed a distance 40cm away from an illuminated objec… - Vidyadip

MCQ

A screen is placed a distance 40cm away from an illuminated object. A converging lens is placed between the source and the screen and it is attempted to form the image of the source on the screen. If no position could be found, the focal length of the lens:

A
Must be less than 10cm.
✓
Must be greater than 20cm.
C
Must not be greater than 20cm.
D
Must not be less than 10cm.

✓

Answer

Correct option: B.

Must be greater than 20cm.

$\text{v}=(40-4)$
$\frac{1}{\text{f}}=\frac{1}{40-4}-\frac{1}{(-\text{u})}$
$\frac{\text{df}}{\text{du}}=0$ for f minimum.
$\frac{\text{df}}{\text{du}}=1-\frac{\text{u}}{20}=0$
$\text{u}=20$
$\text{f}_{\text{min}}=10\text{cm}$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "M.C.Q (1 Marks)" from Geometrical Optics→Geometrical Optics — all question types→Physics STD 11 Science question papers→Gujarat Board STD 11 Science question papers→Gujarat Board question paper generator→

Similar questions

The centripetal acceleration is given by

Two thermometers $A$ and $B$ are exposed in sun light. The valve of $A$ is painted black, But that of $B$ is not painted. The correct statement regarding this case is

If heat given to a system is $6 \,kcal$ and work done is $ 6 kJ.$ Then change in internal energy is ....... $kJ$

Two capillary tubes of same diameter are put vertically one each in two liquids whose relative densities are $0.8$ and $0.6$ and surface tensions are $60$ and $50\, dyne/cm$ respectively Ratio of heights of liquids in the two tubes $\frac{h_1}{h_2}$ is

The mass density of a spherical body is given by $\rho \left( r \right) = \frac{k}{r}$ for $r \leq R\,\,$ and $\rho \left( r \right) = 0\,$ for $r > R$ , where $r$ is the distance from the centre. The correct graph that describes qualitatively the acceleration, $a$, of a test particle as a function of $r$ is

If the ratio of amplitude of wave is $2 : 1$, then the ratio of maximum and minimum intensity is

Two pendulums have time periods $T$ and $\frac{{5T}}{4}.$They start $S.H.M.$ at the same time from the mean position. What will be the phase difference between them after the bigger pendulum has complete one oscillation ..... $^o$

Newtons law are not valid in:

The motion of a particle of mass m is given by $\text{x}=0$ for $\text{t} < 0\ \text{s},$ $\text{x}(\text{t})=\text{A}\sin4\text{p}\ \text{t}$ for $0<\text{t}<(1/ 4)\ \text{s}(\text{A}>\text{o}),$ and $\text{x}=0$ for $\text{t}>(1/4)\ \text{s}.$ Which of the following statements is true?

Two cars are travelling towards each other at speed of $20 \mathrm{~m} \mathrm{~s}^{-1}$ each. When the cars are $300 \mathrm{~m}$ apart, both the drivers apply brakes and the cars retard at the rate of $2 \mathrm{~m} \mathrm{~s}^{-2}$. The distance between them when they come to rest is :