The intensity of a point source of light, S, placed at a distance d in front of a screen A, is I0 at the center of the screen. Find the light intensity at the center of the screen if a completely reflecting plane mirror M is placed at a distance d behind the source, as shown in figure.

Question

The intensity of a point source of light, S, placed at a distance d in front of a screen A, is I0 at the center of the screen. Find the light intensity at the center of the screen if a completely reflecting plane mirror M is placed at a distance d behind the source, as shown in figure. (A) (27 I0/9) (B) (25 I0/9) (C) (17 I0/9) (D) (10 I0/9)

Tardigrade Admin · Accepted Answer

E1=I0=(L/d2), without mirror <img class="img-fluid question-image" alt="image" src="https://cdn.tardigrade.in/img/question/physics/78eda1f93192d861cd870d31b810bfe9-.png" /> and E2=(L/d2)+(L/(3 d)2)=(L/d2)[1+(1/9)]=(10 I0/9) with mirror.

$\frac{27 I _{0}}{9}$

$\frac{25 I _{0}}{9}$

$\frac{17 I _{0}}{9}$

$\frac{10 I _{0}}{9}$

$E_{1} = I_{0} = \frac{L}{d ^{2}}$ , without mirror

and $E_{2} = \frac{L}{d ^{2}} + \frac{L}{( 3 d ) ^{2}} = \frac{L}{d ^{2}} [1 + \frac{1}{9}] = \frac{10 I _{0}}{9}$ with mirror.

Q. The intensity of a point source of light, S, placed at a distance d in front of a screen A, is I0​ at the center of the screen. Find the light intensity at the center of the screen if a completely reflecting plane mirror M is placed at a distance d behind the source, as shown in figure.

927I0​​

925I0​​

917I0​​

910I0​​

E1​=I0​=d2L​, without mirror and E2​=d2L​+(3d)2L​=d2L​[1+91​]=910I0​​ with mirror.

$\frac{27 I _{0}}{9}$

$\frac{25 I _{0}}{9}$

$\frac{17 I _{0}}{9}$

$\frac{10 I _{0}}{9}$

$E_{1} = I_{0} = \frac{L}{d ^{2}}$ , without mirror

and $E_{2} = \frac{L}{d ^{2}} + \frac{L}{( 3 d ) ^{2}} = \frac{L}{d ^{2}} [1 + \frac{1}{9}] = \frac{10 I _{0}}{9}$ with mirror.