Which surface has a positive and which surface has a negative power?

Which lens has positive and which lens has negative power?

Which rubbed body acquires a positive charge and which acquires a negative charge?

Which surface can act as a mirror?

Which planet has life?

Light with enrgy flux of 9 xx 10^5 W m^(-2) falls of a non - refleting surface at normal incidence.If trhe surface has an area of 50 cm^2 ,find average force exerted on the surface during an intervl of 10 minutes.How will the result get modified ,if the surface is a perfect reflector?

Light with an energy flux of 20W//cm^2 falls on a non-reflecting surface at normal incidence. If the surface has an area of 30cm^2 , the total momentum delivered (for complete absorption) during 30 minutes is:

Under what conditions will a convex lens have a negative and a concave lens a positive power?

The magnetic susceptibility for a sample has a small positive value.To which class of magnetic substances, does the specimen belong?