Question Video: Angular Magnification of a Refracting Telescope

What is the angular magnification of a telescope that has a 100 cm-focal length objective and a 2.50 cm-focal length eyepiece?

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Video Transcript

What is the angular magnification of a telescope that has a 100-centimeter focal length objective and a 2.50-centimeter focal length eyepiece?

Let’s call the 100-centimeter focal length objective 𝑓 sub π‘œ and the 2.50-centimeter focal length eyepiece 𝑓 sub 𝑒. We want to know the angular magnification of the telescope, which we’ll call 𝑀.

And to help us in that direction, let’s recall the equation for the angular magnification of a telescope with an objective lens and an eyepiece. The angular magnification of the telescope is equal to negative the focal length of the objective divided by the focal length of the eyepiece.

In our case, since we know both those values, we can plug them in and solve for 𝑀, which we find to be negative 40 times. This means that the size of the image created by this telescope is 40 times larger than the object that it’s imaging.

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