(D) The illuminance $E$ at a distance $r$ from a source of luminous flux $\Phi$ is given by $E = \frac{\Phi}{4\pi r^2}$.Given:$E = 1.57 \times 10^5 \;

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(D) The illuminance $E$ at a distance $r$ from a source of luminous flux $\Phi$ is given by $E = \frac{\Phi}{4\pi r^2}$.Given:$E = 1.57 \times 10^5 \; lm/m^2$$r = 1.5 \times 10^8 \; km = 1.5 \times 10^{11} \; m$Rearranging for $\Phi$:$\Phi = E \times 4\pi r^2$$\Phi = (1.57 \times 10^5) \times 4 \times 3.14 \times (1.5 \times 10^{11})^2$$\Phi = (1.57 \times 10^5) \times 12.56 \times (2.25 \times 10^{22})$$\Phi = 19.7176 \times 2.25 \times 10^{27}$$\Phi \approx 4.43 \times 10^{28} \; lm$.

Class 12 Physics Ray Optics and Optical Instruments Mix Examples-Ray Optics

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When sunlight falls normally on Earth,a luminous flux density (illuminance) of $1.57 \times 10^5 \; lm/m^2$ is produced on Earth. If the distance of Earth from the Sun is $1.5 \times 10^8 \; km$,what is the total luminous flux emitted by the Sun?

A
$4.43 \times 10^{25} \; lm$
B
$4.43 \times 10^{26} \; lm$
C
$4.43 \times 10^{27} \; lm$
D
$4.43 \times 10^{28} \; lm$

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Mix Examples-Ray Optics

Find the luminous intensity of the sun if it produces the same illuminance on the earth as produced by a bulb of $10000 \, cd$ at a distance of $0.3 \, m$. The distance between the sun and the earth is $1.5 \times 10^{11} \, m$.

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Assertion: By roughening the surface of a glass sheet,its transparency can be reduced.
Reason: Glass sheet with a rough surface absorbs more light.

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$A$ film projector magnifies a $100 \; cm^2$ film strip on a screen. If the linear magnification is $4$,the area of the magnified film on the screen is.....$cm^2$.

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In the figure shown,a point object $O$ is placed in air on the principal axis. The radius of curvature of the spherical surface is $60\, cm$. Let $I_f$ be the final image formed after all the refractions and reflections. Which of the following statements is correct?

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$A$ water drop in air refracts the light ray as:

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When sunlight falls normally on Earth,a luminous flux density (illuminance) of $1.57 \times 10^5 \; lm/m^2$ is produced on Earth. If the distance of Earth from the Sun is $1.5 \times 10^8 \; km$,what is the total luminous flux emitted by the Sun?

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Find the luminous intensity of the sun if it produces the same illuminance on the earth as produced by a bulb of $10000 \, cd$ at a distance of $0.3 \, m$. The distance between the sun and the earth is $1.5 \times 10^{11} \, m$.

Assertion: By roughening the surface of a glass sheet,its transparency can be reduced.Reason: Glass sheet with a rough surface absorbs more light.

$A$ film projector magnifies a $100 \; cm^2$ film strip on a screen. If the linear magnification is $4$,the area of the magnified film on the screen is.....$cm^2$.

In the figure shown,a point object $O$ is placed in air on the principal axis. The radius of curvature of the spherical surface is $60\, cm$. Let $I_f$ be the final image formed after all the refractions and reflections. Which of the following statements is correct?

$A$ water drop in air refracts the light ray as:

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Assertion: By roughening the surface of a glass sheet,its transparency can be reduced.
Reason: Glass sheet with a rough surface absorbs more light.