Chapter 19: Optical Instruments
Example Questions Problems
Example 19.1
A pinhole camera is made from an 80-cm-long box with a small hole in one end. If the hole is 5.0 m from a 1.8-m-tall person, how tall will the image of the person on the film be?
Example 19.2
For a patient, a doctor prescribes glasses with a converging lens having a power of 4.0 D.
a. Is the patient nearsighted or farsighted? What is the focal length of the glasses?
b. If another patient uses these glasses and places an object at her near point, where is the image produced?
Example 19.3
The near point for your myopic uncle is 10 cm. Your own vision is normal; that is, your near point is 25 cm. Suppose you and your uncle hold dimes (which are 1.7 cm in diameter) at your respective near points.
a. What is the dime's angular size, in radians, according to you?
b. What is the dime's angular size, in radians, according to your uncle?
a. Do these calculations suggest any benefit to near-sightedness? Explain.
Example 19.4
The objective lens of the refracting telescope at the Lick Observatory in California has a focal length of 57 ft.
a. What is the refractive power of this lens?
b. What focal length (mm) eyepiece would give a magnification of 1000× for this telescope?
Example 19.5
An inexpensive microscope has a tube length of 12.0 cm, and its objective lens is labeled with a magnification of 10X.
a. Calculate the focal length of the objective lens.
b. What focal length eyepiece lens should the microscope have to give an overall magnification of 150X?
Example 19.6
A forensic scientist is using a standard biological microscope with a 15X objective and a 5X eyepiece to examine a hair from a crime scene. How far from the objective is the hair?
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