The only formula you need for this problem is from high school (even middle school) physics class:
. The difficult thing to keep track is what to be substituted in this formula.
First, consider only the first lens. Here
and
. Plugging these values in the formula above, we have
As a result,
.
What does this mean? It means that the image is real and is
behind the first lens. Because the second lens is
behind the lens. It means that the real image is
behind the second lens. That is,
for the second lens.
Now, we can plug this value into the same formula:
As a result,
It means that the resultant image is real and is at
behind the second lens.
The correct answer is (A). 28 of 100 people answered this question correctly.
ฟิสิกส์โอลิมปิก วิทยาศาสตร์โอลิมปิก ข้อสอบแข่งขัน ข้อสอบชิงทุน
