Exam 23: Mirrors and Lenses

The objective lens of a telescope has a focal length of 1.90 m.When viewed through this telescope,the Moon appears 5.25 times larger than normal.How far apart are the objective lens and the eyepiece when this instrument is focused on the Moon?

The focal length of the lens of a simple digital camera is 40 mm,and it is originally focused on a person 25 m away.In what direction must the lens be moved to change the focus of the camera to a person 4.0 m away?

The angular magnification of a refracting telescope is 40.When the object and final image are both at infinity,the distance between the eyepiece and the objective is 143.5 cm.The telescope is used to view a distant radio tower.The real image of the tower,formed by the objective,is 6.0 mm in height.The focal point of the eyepiece is positioned at the real image.What is the focal length of the objective lens?

A person's eye lens is 2.8 cm from the retina,and his near point is at 25 cm.What must be the focal length of his eye lens so that an object at the far point of the eye will focus on the retina?

The closest object that a typical young person with normal vision can see clearly is closest to

An upright object is 50 cm from a concave mirror of radius 60 cm.The character of the image is

A wrench is placed at 30 cm in front of a concave lens with a focal length of magnitude 10 cm.What is the magnification of the wrench?

The power of a lens is 4.0 diopters and its diameter is 5.0 cm.What is the focal length of this lens?

Without glasses,a person can comfortably read a magazine when it is held at 60 cm from his eyes.What should be the focal length of his contact lenses to allow him to read the magazine comfortably at a distance of 30 cm?

Which one of the following statements is correct?

Is it possible to see a virtual image?

A nearsighted person has a far point of 50 cm for his right eye and 150 cm for his left eye.For each eye,what power contact lens will allow the person to see gorgeous sunsets?

Farsightedness can usually be corrected with

A farsighted girl has a near point at 2.0 m but has forgotten her glasses at home.The girl borrows eyeglasses that have a power of +2.75 diopters.With these eyeglasses,what is the near point of the girl,assuming that she wears them extremely close to her eyes?

You have a choice between two lenses of focal lengths f_a and f_b,where f_b = 2f_a,to use as the objective lens in building a refracting telescope.If the magnification you obtain using lens a is M_a,what will be the magnification when using lens b?

A simple compound microscope normally uses

A cup that is 6.0 cm tall is in front of a concave lens.The image of the cup is 2.5 cm tall and 7.5 cm from the lens.What is the focal length of the lens?

An object 2.0 cm tall is placed 24 cm in front of a convex mirror having a focal length of magnitude 30 cm. (a)Where is the image formed and how far is it from the mirror? (b)How tall is the image?

A very delicate sample is placed 0.150 cm from the objective lens of a microscope.The focal length of the objective is 0.140 cm,and that of the eyepiece is 1.0 cm.The near-point distance of the person using the microscope is 25.0 cm.The magnitude of the final magnification of the microscope is closes to

A certain slide projector has a lens of focal length 15.0 cm.This lens forms an image measuring 100 cm × 100 cm on the screen when a slide whose dimensions are 50.0 mm × 50.0 mm is being magnified.How far from the lens should the screen be placed?