A light of intensity $I$ is incident at an angle $\alpha$ with the vertical on a cone with semivertical angle $\theta<\alpha$, height $H$ and radius $R$

▪ Supposing that the cone is perflectly reflecting i.e. does not absorb or transmit

▪ Supposing that cone is perfectly absorbing i.e. does not reflect or transmit

Find the radiation force on cone in both cases.

Note by Prince Loomba
2 years, 9 months ago

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For the 2nd case, I have used projection area. It is semicircle and a semi ellipse,

So we can write area=$\frac {\pi R^{2}}{2}+\frac {\pi RH}{2}$

And then use $IA/c$

Is this approach right?

And I have no idea for the first case

- 2 years, 9 months ago

for the first case the force will become twice of what u have found in the second case .change in momentum will be 2h/lambda .

And if it was a case where here was reflection and absorbtion .then u calculate the force in each case and multiply it with the coefficient of absorbption and reflection respectively (which would be specified in the question )(also to note that a+r=1 where a and r are the coefficients of absorbtion and reflection respectively )

- 2 years, 9 months ago

Exactly twice, are you sure? And I havent really found a proof for other half to be ellipse, can you find?

- 2 years, 9 months ago

ill try proving it .

- 2 years, 9 months ago

Thanks

- 2 years, 9 months ago

how did u conclude that it would be an area of ellipse only in the first part ?

- 2 years, 9 months ago

I havent. For second I said its half ellipse half corcle, with no proof

- 2 years, 9 months ago