Size of image

[karimretina]

Hi, who can solve this problem?
A distant object subtends an angle of 10 degree;find the size of the image formed by the +4D lens .
Actually,my answer is -0.044m (i.e. 4.4 cm inverted image).however, the answer key is 4.37cm !!!!!!
Thank you

[HarryChiling]

Hi, who can solve this problem?
A distant object subtends an angle of 10 degree;find the size of the image formed by the +4D lens .
Actually,my answer is -0.044m (i.e. 4.4 cm inverted image).however, the answer key is 4.37cm !!!!!!
Thank you

It looks like they converted the degree measure to radians before multiplying the focal length by the tangent of the angle. In either case the error is negligable IMO, but the radian measure is going to provide more accuracy.

[Darryl Meister]

The most accurate answer will be just over 4.40 cm, assuming that the lens is "thin." But if the author relied on a small angle approximation to determine the answer, instead of using the actual tangent of the angle, the result will be closer to 4.36 cm.

You can read an article on ray tracing thin lenses at OptiCampus.com: Ray Tracing Thin Lenses, which will cover many of the formulas and fundamentals involved.

Best regards,
Darryl

[Matevz]

surely over 4.40 cm