SOLUTION: A small spherical light source is 1.8m above the centre point of a square table of a side of 2 figure 1. the illuminance E at the centre point of the table is 300 lx. calculate

Algebra ->  Numeric Fractions Calculators, Lesson and Practice -> SOLUTION: A small spherical light source is 1.8m above the centre point of a square table of a side of 2 figure 1. the illuminance E at the centre point of the table is 300 lx. calculate       Log On


   

Question 935922: A small spherical light source is 1.8m above the centre point of a square table of a side of 2 figure 1. the illuminance E at the centre point of the table is 300 lx.
calculate the ecrnr at the tip of the table.
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Calculate the distance from the bulb to the corner of the table (I assume that's what you mean by tip).
R%5E2=1.8%5E2%2B1%5E2%2B1%5E2
R%5E2=3.24%2B1%2B1
R%5E2=5.24
Illuminance is inversely proportional to the square of the distance.
k%2F1.8%5E2=300
k%2F5.24=X
X=300%283.24%2F5.24%29
X=185.5lx
Since the distance from the source to the edge of the table is 1.8 down, 1 up, and 1 over, the source is no longer directly over the point but at an angle,+theta.
tan%28theta%29=sqrt%281%5E2%2B1%5E2%29%2F1.8
theta=38.2 degrees
En=X%2Acos%28theta%29=185.5%2Acos%2838.2%29=145.7 lx