The illuminance of sunlight on the earth for normal incidence is `2.5 xx 10^5`lux. If the distance between earth and sun is `1.5 xx 10^11` m. Calculate:
luminous intensity of the sun.

A boy is trying to start a fire by focussing sunlight on a piece of paper using an equiconvex lens of focal length 10 cm.The diamerter of the sun is 1.39 xx 10^9 m and its mean distance form the earth is 1.5 xx 10^(11) .What is the diameter of the sun's image on the paper?

In a two-slit experiment with monochromatic light, fringes are obtained on the screen placed at some distance form the slits. If the screen is moved by 5 xx 10^-2 m towards the slits, the change in fringe width is 3 xx 10^-5 m . If the distance between the slits is 10^-3 m , calculate the wavelength of the light band.

A magnet weighs 75 g and its magnetic moment is 2xx10^-4 A m^2 . If the density of the material of the magnet is 7.5 xx 10^3 kg m^-3 , calculate the intensity of magnetisation.

How will you ‘weigh the sun’, that is estimate its mass? The mean orbital radius of the earth around the sun is 1.5 xx 10^8 km .

If the distance between the sun and the earth is increased by three times then attraction between two will:

The distance between the sun and the Saturn in 1433500000000 m or 1.4335xx10^(12)m The distance between Saturn and Uranus is 1439000000000 m or 1.439xx10^(12)m The distance between the sun and the earth is 149600000000 m or 1.496xx10^(11)m Can you tell which of the three distances is smallest?

The rate constant of a reaction is 1.5 xx 10^7 sec^(-1) at 50^@ C and 4.5 xx 10^7 sec^(-1) at 100^@ C . Calculate energy of the activation for the reaction.