A telescope uses one long focal length lens (objective lens) and one short focal

Question

A telescope uses one long focal length lens (objective lens) and one short focal length lens (eyepiece, where you put your eye).
Tom's homemade telescope consists of two convex lenses with a common principal axis: the eyepiece (focal length feye = 5.61 cm) and the objective lens (focal length fobj = 40.7 cm). He is looking through the eyepiece of his telescope at an object 7.61 m beyond the objective lens. If the telescope tube is adjusted so the distance between the lenses is 0.47 m, find
i. The distance from the eyepiece to the image created by the telescope eyepiece: cm
ii. The magnfication of Tom's telescope: ____________

Explanation / Answer

Part 1)

For the objective, apply 1/f = 1/p + 1/q

1/40.7 = 1/761 + 1/q

q = 43.0 cm

Then, for the eyepeice

1/5.61 = 1/4 + 1/q

q = -13.94 cm

Thus the distance from the eyepiece is 13.94 cm in front of the eyepeice (That is why q was -13.94 from the calculation above. Your answer key may want the negative, so try it if it does not like the positive value)

Part 2)

M for a telescope = fo/fe

M = 40.7/5.61

M = 7.25

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.