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Question on Lenses

can anyone pls help me with this question?
"Sketch the three refracted rays and locate the image (I)."
i know the second ray is parallel to the principal axis and it will lies on F.
but what about the other two?
pls help me
thx

Reply 1

stumpy07

The parallel ray is bent so that it passes thruough the F on the right (Fr).
Construct a line from O through the exact centrepoint of the lens and out to the right.
You now have 2 diverging lines on the right. Extend these back over to the LHS till they join to form the point O' on the left - the virtual image. Now draw the other lines from the lens back to the image O', and then extend to the right, this gives you the right angle of refraction.

Edit - Pic attached. Red lines are extended back via blue to give O'