A black metal foil is warmed by radiation from a sphere at temperature Tat a distance d. If the power received is P, find the power received when both the temperature and distance are doubled.

A spherical black body with radius 12 cm radiates 450 W power at 500K,If the radius were halved and the temperature doubled,the power radiated in watt would be

Lenses of power 3D and - 5D are combined to from a compound lens. An object is placed at a distance of 50 cm from this lens. Find the position of its image ?

A convex lens forms a real and inverted image of a needle at a distance of 50 cm. from it . Where is the niddle placed in front of convex lens if the image is equal to the size of the object? Also , find the power of the lens.

Find the power of the eye lens of the normal eye when it is focussed at its near point. Assume the distance of the retina from the eye lens to be 2.5 cm.

In a Young's double slit experiment distance between the slits is 1 mm. The fringe width is found to be 0.6 mm. When the screen is moved through a distance of 0.25 m away from the plane of the slit, the fringe width becomes 0.75 mm. Find the wavelength of light used.

About 10% of the power of a 100W light bulb is converted to a visible radiation. What is the average intensity of visible radiation. at a distance of 1m from the bulb?