Question

A laser emitted a 0.1 ms long pulse of light with total energy 10 J. The average pressure of such a pulse focused on a spot of diameter 1mm on a fully reflective surface is:

Answer 1

As the laser is focused on a spot and it will be given that the light is totally reflected.Thus we can not take the absorption part into account.
a 0.1 ms prise of light- A laser emitted a oil with lotal e Hence given long jone. energy 40 this is that purse of radiation 0.1 ms and energy ressure such right pusse when it is d - Imm f E = 10 joule This is also cleared to us that the means press exerted focussed into a spot having diameter As the laser beam is totally reflected so it a reflection. co-efficient P = 1 The mean pressure to the forece exerted by leny possessing Now is LP) is related the beam وك LP) Tid2 - f where f equals the momentum transferred per se cond. the photone reflection the equh of force is 2P+(-P) & = (1+0) - (0)

Hence, momentum the 15+ term represents the Iransferred on reflection The second terecon represents the absorption factor. there is no absorption fully (100%) reflected to the second terem goes vanish . Cegunii average preessure is As hence occures leat So the 2PE して LP3 f nd/ nd/ 2P. € * 4. CT T d2 8x1 x 10 4 3x 108 X1 71x/ 103 o.1 ms sec- 1000 1 mm = = 8995-39 ato prenowned average pressure is 3395.33 atmospheric frenaure. The an. 10oo