Question

light with energy flux of 18w/cm² falls on a non reflecting surface of area 20cm2 at normal incidence the momentum delivered in 30 minutes is​

Answer 1

☛Given-

Change in time= 30 min

Surface area = 20 cm²

Intensity of light = 18 w/cm²

   

☛Find-

Momentum-?

     

☛Formula used -

$\bf{P= \dfrac{IAt}{C} }$

where,

P = momentum,

I= current,

A= surface area,

t= time taken

   

☛ SoLution-

First change Time min to sec.

1min.= 60sec

1×30 min. = 60× 30 sec.

30min. = 1800 sec.

Total power exerted by surface =>

$\bf{P = \dfrac{U}{C} }$

$\bf{P= \dfrac{IAt}{C} }$

$\bf{P = \dfrac{ 18 \times 20 \times 1800 }{3 \times 10^8 } }$

$\bf{ P = 2.16 \times 10^{-3} kgm/s }$

$\underline{\pink{\bf{ \therefore Momentum \ is \ 2.16 \times 10^{-3} kgm/s }}}$

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