Download App

Geometrical Optics — Physics STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 SciencePhysicsGeometrical Optics1 Mark
Question
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:
  1. Must be less than 10cm.
  2. Must be greater than 20cm.
  3. Must not be greater than 20cm.
  4. Must not be less than 10cm.
✓

Answer

  1. Must be greater than 20cm.
Explanation:
$\text{v}=(40-4)$
$\frac{1}{\text{f}}=\frac{1}{40-4}-\frac{1}{(-\text{u})}$
$\frac{\text{df}}{\text{du}}=0$ 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 12 Science question papers→Rajasthan Board STD 12 Science question papers→Rajasthan Board question paper generator→

Similar questions

Water boils in an electric kettle in 15 minutes after switching on. If the length of the heating wire is decreased to 2/3 of its initial value, then the same amount of water will boil with the same supply voltage in(a) 15 minutes(b) 12 minutes(c) 10 minutes(d) 8 minutes
       
→
A metal plate is getting heated. It can be because:
→
The current in a coil changes from 4 ampere to zero in 0.1 s. If the average e.m.f. induced is 100 volt, what is the self inductance of the coil(a) 2.5 H(b) 25 H (c) 400 H (d) 40 H
       
→
The wavefronts of a light wave travelling in vacuum are given by $x + y + z = c.$ The angle made by the direction of propagation of light with the $X-$axis is:
→
The value of emitted frequency is maximum, while transition of electron :
→
Which of the following is used as a moderator in nuclear reactors(a) Uranium(b) Heavy water(c) Cadmium(d) Plutonium
       
→
A current carrying coil is placed with its axis perpendicular to $N-S$ direction. Let horizontal component of earth's magnetic field be $\mathrm{H}_{\mathrm{o}}$ and magnetic field inside the loop is $H.$ If a magnet is suspended inside the loop, it makes angle $\theta$ with $H .$ Then $\theta=$
→
A capacitor acts as an infinite resistance for:
  1. DC.
  2. AC.
  3. DC as well as AC.
  4. Neither AC nor DC.
→
The light reflected by a plane mirror may form a real image(a) If the rays incident on the mirror are diverging(b) If the rays incident on the mirror are converging(c) If the object is placed very close to the mirror (d) Under no circumstances
 
 
 
 
→
Potentiometer measures potential more accurately because:
→