Thora leans a magnifying glass close over a page of tiny print. The letters look bigger and right-way-up, floating somewhere behind the glass. When she lifts the lens a little higher, they swell even more.
You constructed this case last lesson: the object inside the focal point. Now the result gets stated as a profile you can quote without drawing.
Put any object inside the focal point of a convex lens, closer to the glass than one focal length.
The construction always ends the same way: the beam's refracted rays spread, and their dashed trace-backs meet on the object's own side.
Virtual: only the trace-backs meet, so no screen catches it; you see it by looking through the lens.
Upright: the trace-back meeting sits on the same side of the principal axis as the object's tip, so nothing flips.
Enlarged: the meeting sits farther from the lens than the object, and higher than its tip, so the seen picture is bigger than the thing.
Thora's print sits closer than one focal length, so the profile applies: big, right-way-up letters, viewed through the glass.
This profile belongs to ONE position. Slide the object past the focal point and the lens switches to the other ending: real and inverted.
A coin lies 4 cm under a convex lens of focal length 9 cm. Describe the image a viewer sees through the lens.
4 cm is less than 9 cm, so the coin sits inside the focal point.
The profile applies: virtual, upright, enlarged.
The viewer looks through the lens and sees a bigger, right-way-up coin; no screen could catch it.
The image is virtual, upright, and enlarged: a magnified coin seen through the glass.
Quill uses the same lens on the same coin, but holds the lens so the coin sits 14 cm away. Does the magnifier profile still apply?
14 cm is more than 9 cm, so the coin now sits beyond the focal point.
The magnifier profile belongs only to the inside-the-focal-point position.
Beyond the focal point the construction ends in an actual crossing: real and inverted.
No. Past the focal point the lens gives the other profile: a real, inverted image.
An object sits inside the focal point of a convex lens. Describe the image.
For which object position does a convex lens work as a magnifying glass?
Romilly says: 'Hold a convex lens over print, closer than one focal length, and you see the letters bigger and right-way-up.' Is Romilly correct?
A pressed flower sits inside the focal point of a convex lens. Which description of its image is correct?
Thora's stamp sits 5 cm from a convex lens of focal length 10 cm. She slides it out to 20 cm. What happens to the image?
Where must a viewer look to see the enlarged image a magnifying glass makes?