1.

Solid angle subtended by hemisphere at centre is ...... .

Answer»

1sr
`2PI sr`
`4PI sr`
`pi sr`

Solution :Surface area of sphere of radius `r=4pi r^(2)`
`:.` Surface are of HEMISPHERE `DeltaA=2pi r^(2)`
`:.` Solid ANGLE `=(DeltaA)/(r^(2))=(2pir^(2))/(r^(2))=2pi sr`


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