A POINT SOURCE OF LIGHT IS PLACED 50 CM ABOVE A CIRCULAR CARD OF DIAMETER 5CM, THE SOURCE BEING DIRECTLY ABOVE THE CENTRE OF THE CARD. WHAT IS THE AREA OF THE SHADOW ON THE FLOOR 70 CM BELOW THE CARD?
The diameter of the shadow is D = 5 cm immediately below the circular card. At distances farther below the card, the diameter of the shadow grows in proportion to the distance from the point source.
70 cm below the card is 120 cm from the point source. The diameter of the shadow there is (120/50)*5 = 12 cm
The area of the shadow there would be
(pi/4)*12^2 = 36 pi = 113.1 cm^2
THANK YOU!
WHAT DOES PI STAND FOR?
Sabrina,
pi is an irrational number approximated by 3.14159
It is the ratio of the circumference of a circle to the diameter.
C = pi D
the area of the circle is ten
A = pi R^2 = pi (D^2)/4
the area of the circle is then
A = pi R^2 = pi (D^2)/4
pi = 3.141592...
It is the ratio of the circumference to the radius of a circle.
It is usually represented by a Greek letter, but I cannot type it here.
thank you
would what the nature of the shadow be if the point of source of light is replaced by a luminous disc of diameter 5 cm, whose centre lies directly above the centre of the card?
pe·num·bra/peˈnəmbrə/
Noun:
The partially shaded outer region of the shadow cast by an opaque object.
The shadow cast by the earth or moon over an area experiencing a partial eclipse.
thank you
what would the dimension of shadow be?
directly below the card, dark
after you get out from that complete shadow, you can look up and see part of the light so you are in partial shadow until you get far enough out to see the entire light.