Home
Class 12
PHYSICS
10 % of the total energy of a 100 W bulb...

10 % of the total energy of a 100 W bulb is converted into visible light. Calculate the average intensity out a spherical surface which is at a distance of 1m from the bulb, consider the bulb to be a point source and let the medium be isotropic.

Text Solution

Verified by Experts

Electrical energy used per second in bulb,
U = P of `10%=100xx0.1`
`therefore U=10 J`
Considering bulb as centre, area of circular surface
`A=4pi d^(2)=4xx3.14xx(1)^(2)=12.56m^(2)`
Average intensity on circular surface
`I=(U)/(A)=(10)/(12.56)=0.796 Wm^(-2)`
`therefore I=0.8 Wm^(-2)` (Approximate).
Promotional Banner

Topper's Solved these Questions

  • ELECTROMAGNETIC WAVES

    KUMAR PRAKASHAN|Exercise SECTION C NCERT EXEMPLAR SOLUTION (Multiple Choice Questions)|13 Videos

  • ELECTROMAGNETIC WAVES

    KUMAR PRAKASHAN|Exercise SECTION C NCERT EXEMPLAR SOLUTION (Very Short Answer Type Questions)|7 Videos

  • ELECTROMAGNETIC WAVES

    KUMAR PRAKASHAN|Exercise SECTION B NUMERICALS (Numerical From Textual Exercise)|35 Videos

  • ELECTROMAGNETIC INDUCTION

    KUMAR PRAKASHAN|Exercise Section D MCQs (MCQs asked in Competitive Exams )|38 Videos

  • ELECTROSTATIC POTENTIAL AND CAPACITANCE

    KUMAR PRAKASHAN|Exercise Section D ( MCQs asked in Cometitive Exams )|39 Videos

Similar Questions

Explore conceptually related problems

3% of energy of 100 W bulb is converted into visible light. Find the average intensity on a spherical surface 1 m away from the bulb consider the bulb is point source and medium is isotropic.

About 5% of the power of a 100 W light bulb is converted to visible radiation. What is the average intensity of visible radiation : at a distance of 1m from the bulb ?

About 5% of the power of a 100 W light bulb is converted to visible radiation. What is the average intensity of visible radiation (a) at a distance of 1m from the bulb? (b) at a distance of 10 m? Assume that the radiation is emitted isotropically and neglect reflection.

About 5% of the power of a 100 W light bulb is converted to visible radiation. What is the average intensity of visible radiation : at a distance of 10 m ? Assume that the radiation is emitted isotropically and neglect reflection.

A bulb of 100 W electrical power emits visible light with 3% efficiency. Find amplitude of oscillations of electric field at 5 m from the bulb.

Calculate the electric and magnetic fields produced by the radiation coming from a 100 W bulb at a distance of 3 m. Assume that the efficiency of the bulb is 2.5% and it is a point source.

Consider a 20 W bulb emitting light of wavelength 5000 Å and shining on a metal surface kept at a distance 2m.Assume that the metal surface has work function of 2eV and that each atom on the metal surface can be treated as a circular disk of radius 1.5 Å. (i)Estimate no. of photons emitted by the bulb per second.[Assume no other losses] (ii)Will much time would be required by the atomic disk to receive energy equal to work function (2eV)? (iv)How many photons would atomic disk receive within time duration calculated in (iii)above? (v) Can you explain how photoelectric effect was observed instantaneously?

Two identical glass rods S_(1) and S_(2) (refractive index=1.5) have one convex end of radius of curvature 10 cm. They are placed with the curved surfaces at a distance d as shown in the figure, with their axes (shown by the dashed line) aligned. When a point source of light P is placed inside rod S_(1) on its axis at a distance of 50 cm from the curved face, the light rays emenating from it are found to be parallel to the axis inside S_(2) . The distance d is

A small bulb is placed at the bottom of a tank containing water to a depth of 80cm. What is the area of the surface of water through which light from the bulb can emerge out? Refractive index of water is 1.33. (Consider the bulb to be a point source.)