In a refracting telescope, the angular magnification is greater than 1 when which condition holds?

In a refracting telescope, the angular magnification is greater than 1 when which condition holds?

• A. fo > fe
• B. fo < fe
• C. fe > fo
• D. fo = fe

Answer: (A)

In a refracting telescope, the angular magnification comes from how the two lenses work together: the objective with focal length fo forms an image, and the eyepiece with focal length fe magnifies that image. The angular magnification is approximately fo divided by fe (taking magnitude, the sign would indicate inversion). So to get magnification greater than 1, the ratio fo/fe must be greater than 1, which means fo is larger than fe. When the objective’s focal length is longer than the eyepiece’s, the telescope makes the incoming light bend into rays that spread out more at the eyepiece, producing a larger angle for the final image. If fo were smaller than fe, the magnification would be less than 1. If they were equal, the magnification would be exactly 1.

In a refracting telescope, the angular magnification comes from how the two lenses work together: the objective with focal length fo forms an image, and the eyepiece with focal length fe magnifies that image. The angular magnification is approximately fo divided by fe (taking magnitude, the sign would indicate inversion).

So to get magnification greater than 1, the ratio fo/fe must be greater than 1, which means fo is larger than fe. When the objective’s focal length is longer than the eyepiece’s, the telescope makes the incoming light bend into rays that spread out more at the eyepiece, producing a larger angle for the final image.

If fo were smaller than fe, the magnification would be less than 1. If they were equal, the magnification would be exactly 1.