Theory

a) How can you move a spacecraft just with solar radiation?

b) Explain how nanoparticle sunscreens can be transparent to thehuman eye, but still protect the skin.

c) What are the two main ways that nanoparticle sunscreenscontaining TiO2 or ZnO can protect your skin from ultravioletradiation? [Note: the UV wavelengths of most concern are labelledUV-A (400-315nm) and UV-B (315-280nm)].

d) What is the largest size of TiO2 nanoparticle that could beused to make a transparent sunscreen (before to apply it)? [Hint:use the size parameter and wavelength of 500 nm]

e) What other factors would you need to consider before reducingthe particle size to make a sunscreen transparent?

f) What colour would be the sky at noon (assuming normalincidence of the sun rays) if the atmosphere was made by 10 umparticles?

g) Explain why is possible to do sensing with plasmonicnanoparticles.

h) Explain the working principle of a microwave oven. Would itstill work if you doubled the wavelength of the excitingradiation?

i) Is it possible to detect spherical particles in air with adiameter of 1nm with the IR light? Comment the answer.

j) Is the Rayleigh scattering at λ=400 nm greater or smallerthan the one at λ=700 nm for equal incident intensity of light?Explain the answer.