1. The problem statement, all variables and given/known data An EM wave with intensity=200 W/m^2 is normal to a black .2m x .3m card that absorbs 100% of the wave. (a) Find the force exerted on the card by the radiation. (b) Find the force exerted by the same wave if the card reflects 100% of the light. 2. Relevant equations Pr=I/c Pressure=F/A 3. The attempt at a solution Part (a) I solved. (I/c)(0.2*0.3)=F=4*10^-8 N Part (b) I know is double the force. My question is conceptual. Why is the force doubled when the EM wave is reflected? Thank you for any and all replies.