Microscope

            The microscope is a tool that is used to view small specimins.  The specemin is magnified so that we can see the different parts of it.  A microscope consists of an eyepiece which is attached to an objective, and a plate.  The plate holds the specimin, and there is either a light source or a mirror under the plate.  The mirror serves the purpose of the light source, because by moving it, light from the room can be sent into the microscope.

            The Case 4 situation is used with the microscope.  The object is placed between f and 2f.  The total magnification is determined by the product of the magnification of the eyepiece and the magnification of the objective.  The magnification of the eyepiece and the magnification of the objective must be calculated separately.  There are two basic equations involved in finding the magnification.  The first is 1/f=1/d_i + 1/d_o, and the second is d_i/d_o = s_i/s_o = magnification.  For our purposes, the distance to the image for the eyepiece will be 25 cm, which is the near point for a normal eye.  In a problem, another variable must be given in order for you to calculate anything.  For instance, they might give the magnification, the focus length, or the length of the barrel of the microscope.  In the case of the latter, keep in mind that the distance to the image for the objective added to the distance to the object for the eyepiece will equal the barrel length. 

Example:

            A microscope with a barrel length of 20cm has an eyepiece with an objective with a magnification of 10.  The objective’s focus is 0.5cm.  What is the total magnification of this microscope?

Answer: 

Barrel length:  20cm

eyepiece magnification:  10

Objective’s focus:  0.5cm

d_i for eyepiece = 25cm

eyepiece

            Magnification = d_i/d_o

            10 = 25/d_o

            d_o = 2.5cm

Objective

            d_i = barrel length – d_o(eyepiece)

            d_i = 20 – 2.5

            d_i = 17.5cm

            1/f = 1/d_i + 1/d_o

            1/0.5 = 1/17.5 + 1/d_o

            d_o = 0.5cm

            Magnification = d_i/d_o

            Magnification = 17.5/0.5

            Magnification = 35

Total Magnification

            M_T = M_eyepiece x _Mobjective

            M_T = 10 x 35

            M_T = 350

Therefore the total magnification for this microscope is 35

Visit in the fun section: How to Make a Microscopie