Consider two solid spheres of radii $R_1=1\mathrm{m}$ ${}_{}$ , $R_2=2m$ ${}_{}$ and masses $M_1$ ${}_{}$ and $M_2$ ${}_{}$ , respectively. The gravitational field due to sphere (1) and (2) are shown. The value of $\frac{M_1}{M_2}$ $\frac{{}_{}}{{}_{}}$ is:

 

When a soap bubble is illuminated by source of white light, it appears coloured. This is due to

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