Question

• Differentiate between a compound microscope and a stereomicroscope (dissecting microscope) in terms of: i. Magnification (which of the two microscopes has a higher magnification); ii. Working distance (which of the two microscopes has a larger working distance) – look in Lab Protocol section to determine definition of working distance; iii. Type of image formed by microscope (one of the microscope produces an erect image while the other produces an inverted image) – look in Lab Protocol section to determine definition of these types of images; Type of specimen viewed; Size (one of the microscopes is better for small, thin specimens while the other is better for large, thick specimens) Number of objective lenses (one of the microscopes has four objective lenses while the other has two objective lenses) vi. Location of light source (one of the microscopes has the light source below the stage while the other has the light source above the stage) iv. V

Answer 1

1) ans- Magnification

Compound microscope is used where higher magnification is required to study internal structure of cells eg- blood cells , bacteria , skin etc .varies from 40x to 1000 x .

Stereomicroscope is used for lower magnification for dissection of larger object eg- flower , rocks , insects .Varies from 6x to 50x

2) Working distance - definition - distance between microscope lens and focussed object.

Compound microscope (CM) have a fairly small working distance ,varies from 0.14 - 4 millimetres.

SM varies from 25- 150 millimetres . used durin dissection eg- watch repair .

3) Type of image formed

In compound microscope - It is an optical devices which uses two lenses primary lens forms real imge aand sevondar lens is used as a magnifier to make an enlarged virtual image . When an object is placed farther from a convergent lens than the focal length , tbe lens produced an inverted , real and enlarged image . Image formed by stereo microscope is inverted . .( Inverted image means that the imge is upside down when compared to the object .)

An image in which directions are the same as those in the object, in contrast to an inverted imaage is called an erect image . It is the one that appears right side up.

4) Type of specimen viewed

Compound microscope - specimen are thin enough that light can pass through them from below. It is designed for viewing small cells or thin sections of orgns or tissues placed on a glass mounting side.

Stereomicroscope - large specimen such animals plant nd organs .

5) No of objective lenses-

Compound microscope are typically supplied with 3_4 objective lenses .

Stereo microscope use 2 objective lenses to generate 3 dimensional image .

6) Location of light source

Compound microscope- light is passed through the sample ( called transmitted light illumination ) i.e rely on light shining from beneath the specimen.Larger objects need to be sliced to allow this to happen efficiently .

Stereomicroscope - using incident light illumination ( light reflected off the surface of the sample observed by the user ) . Although it can also be combined with transmitted light in same instrument.