One change, explained
Why does the image move away as the candle approaches?
Move a candle and use three principal rays to follow the position and size of its real image.
Start with the question
As the candle approaches the focal point, why does the sharp real image move farther from the lens?
A converging lens must bring rays from one object point back together. When object distance decreases but remains beyond the focal length, those rays travel farther after the lens before crossing, so image distance and magnification increase.
Change just this
Change the object distance from 35cm to 25cm and watch where the image starts.
scene candle_lens_distance
object candle height=5cm #gold
lens L type=converging focal_length=10cm #blue
candle images through L 35cm #red
drive candle object_distance=16cm duration=5s
show principal_rays image_distance magnificationscene candle_lens_distance
object candle height=5cm #gold
lens L type=converging focal_length=10cm #blue
candle images through L 25cm #red
drive candle object_distance=16cm duration=5s
show principal_rays image_distance magnificationCompare before and after
Why does the image move away as the candle approaches?
01Object distance: 35 cm
Diagram description
Animated physics diagram: candle_lens_distance; showing object distance, image distance, magnification.
02Object distance changed to 25 cm
Diagram description
Animated physics diagram: candle_lens_distance; showing object distance, image distance, magnification.
The physics behind it
As the candle approaches the focal point, why does the sharp real image move farther from the lens?
Keep the focal length at 10 cm. Changing object distance from 35 cm to 25 cm moves the real image from about 14 cm to about 16.7 cm. Near the focal point, the image recedes rapidly.
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