PH 202

Quiz # 09 (10 pts)

Name

Solution

 

A  tall object is located  to the left of a lens.  The image formed by the lens is  tall and located  to the left of the lens.  Is this a converging or diverging lens, and what is the focal length of the lens?

 

A.

Diverging

C.

Converging

 

 

 

 

B.

Diverging

D.

Converging

 

 

 

 

- sign indicates diverging lens!

 

So Correct Answer is B !

 

A  object is  to the left of a lens.  The image is found to be  tall and upright.  What is the focal length of the lens, and it is a diverging or converging lens?

 

A.

Diverging

C.

Converging

 

 

 

 

B.

Diverging

D.

Converging

 

So image distance is

 

Now find focal length

 

 

 

 

- sign indicates diverging lens!

 

So Correct Answer is A !

 

An object is located  to the left of a converging lens with a focal length of .  A diverging lens with a focal length of  is placed  to the right of the converging lens.  Where is the final image of the two lenses formed, relative to the diverging lens?  Is this image upright or inverted?

 

A.

 to right of diverging lens and Upright

 

 

B.

 to left of diverging lens and Inverted

 

 

C.

 to right of diverging lens and Inverted

 

 

D.

 to left of diverging lens and Upright

 

The first lens creates an image found from

 

 

This is to the right of the converging lens.  This is a real image and would therefore be inverted.  So, with the second lens 30 cm to right of converging lens, this image acts as the object of the second lens. 

 

 

Note: the – sign indicates a virtual object.  Now find the second image.

 

 

 

 

This is positive so it is a real image 4.99 cm to right of diverging lens.  Now since the object was virtual the image retains the same orientation, so the virtual object was inverted since the first image was real and inverted.  Thus, the final image is also inverted.

 

Also consider the magnifications

 

 

So  is negative, so  is negative and image is inverted!

 

So Correct Answer is C !

 

A person has a far point (distance which they can see clearly without corrective lenses) of .  They would like to be able see objects up to  away.  What type of contact lenses (converging or diverging) and with what focal length should the lens have to correct their vision?

 

A.

Converging lens

C.

Diverging lens

 

 

 

 

B.

Converging lens

D.

Diverging lens

 

So the image distance is the far point but remember this is a virtual image so,

, while the object distance is the distance you want to now make out or .  Use the lens equation

 

 

 

negative focal length, so diverging lens!

 

So the Correct Answer is D !

 

A person has a near point of .  What should be the focal length of a lens, which sits  from their eye, which would allow them to read at the usual near point of ?

 

A.

C.

 

 

 

 

B.

D.

 

So the image distance is the near point but remember  first you need to subtract off the  distance to the eye, and remember this is a virtual image so,

, while the object distance is the distance you want to now make out or

.  Use the lens equation

 

 

 

So Correct answer is B !

 

 

 

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This page last updated on November 6, 2020