Download App

Photometry — Physics STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 SciencePhysicsPhotometry1 Mark
MCQ
A photographic plate is placed directly in front of a small diffused source in the shape of a circular disc. It takes $12s$ to get a good exposure. If the source is rotated by $60^\circ$ about one of its diameters, the time needed to getthe same exposure will be:
  • A
    $6s$
  • B
    $12s$
  • ✓
    $24s$
  • D
    $48s.$
✓

Answer

Correct option: C.
$24s$
Here,
$\text{t}_1=12\text{s}$
$\theta_1=0^0$
$\theta_2=60^0$
$\text{t}_2=?$
Let the distance be $r.$
Let the incident luminosity be $E_o$.
We have,
$\text{E}_{\theta1}=\frac{\text{E}_\text{o}\cos\theta_1}{\text{r}^2}$
$\text{t}_1 \alpha\frac{1}{\text{E}\theta_1}$
$\Rightarrow\text{t}_1=\frac{\text{r}^2\text{k}}{\text{E}_\text{o}\cos\theta_1}$
$\Rightarrow12=\frac{\text{r}^2\text{k}}{\text{E}_\text{o}\cos0}$
$\Rightarrow \frac{\text{r}^2\text{k}}{\text{E}_\text{o}}=12$
Simiolarly,
$\text{t}_2=\frac{\text{r}^2\text{k}}{\text{E}_\text{o}\cos\theta_2}=\frac{12}{\cos(60^0)}$
$\Rightarrow\text{t}_2=12\times2=24\text{s}$

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 "1 Marks Question" from Photometry→Photometry — all question types→Physics STD 12 Science question papers→Rajasthan Board STD 12 Science question papers→Rajasthan Board question paper generator→

Similar questions

Two bulbs of 25 W and 50 W are joined in series. Which will give more light and why?
→
Write name of that part of electro-magnetic spectrum whose wavelength is $10^{-2} m$ and write its one use also.
→
On what does the value of magnification ( $m$ ) depend in a concave mirror and what type is the value of $( m )$ always in a convex mirror?
→
What is the function of a dielectric in a capacitor?
→
Under what condition does a biconvex lens of glass having a certain refractive index act as a plane glass sheet when immersed in a liquid? 
→
Write the formula of Coulomb's law in vacuum or air.
→
A charge $'q\ '$ is moved from a point $A$ above a dipole of dipole moment $'p\ '$ to a point $B$ below the dipole in equatorial plane without acceleration. Find the work done in the process.
→
What is the process of spontaneous disintegration of an element called?
→
What is internal resistance of a cell?
→
For the telescope described in, what is the separation between the objective lens and the eyepiece?
→