What protects us from UV light emitted by the sun ?

The sun gives light at the rate of 1400Wm^(-2) of area perpendicular to the direction of light. Assume lamda(sunlight)=6000A . Calculate A.the number of photons per second arriving at 1 m^2 area at earth. B. the number of photons emitted from the sun per second assuming the average radius of the Earth's orbit is 1.49xx10^(11) m.

If the efficiency of an electric bulb of 1 watt is 10% what is the number of photons emitted by it in one second ?(The wavelength of light emitted by it is 500 nm.)( h=6.625xx10^(-34)J.s).

According to the classical electromagnetic theory, calculate the initial frequency of the light emitted by the electron revolving around a proton in hydrogen atom.

If a woman is using a copper-T will it help in protecting her from sexually transmitted diseases ?

A system is created by adjusting the five polaroids to touch each other. The polaroid rotates one by one about its axis to 60^(@) . Then intensity of emergent light emitted from the last polaroid will be the ...... part of intensity of incident light.

What is the energy in joules requried to shift the electron of the hydrogen atom from the first Bohr orbit to the fifth bohr orbit and what is the wavelength of the light emitted when the electron returns to the ground state ? The ground state electron energy is 2.18 xx 10^(1) ergs