3.3 Microscopic measurements and calculations
No description yet. This curated deck is ready for daily study.
Card preview (5)
How can you measure the size of objects in a light microscope
. Use an eyepiece graticule
What is a graticle and what is etched onto it
. A glass disc that is placed in the eyepiece of a microscope . A scale is etched onto it which is typically 10mm long and is divided into 100 sub divisions
Why can’t the scale on the eyepiece graticule be used directly to measure the size of objects under a microscopes objective lens What must be done to fix this
Each objective lens magnifies to a different degree, so the graticule must be calibrated for a particular objective lens. However once calibrated it can remain in place for future use as long as the same objective lens is used
How do you calibrate the eyepiece graticle
. You use a special microscope slide called a stage micrometer . This slide has a scale etched onto it and the scale is 2mm long and has sub divisions that are 0.01mm . So as a result: for example 10 units on a qm scale are equivalent to 40 units on a graticule scale So 1 unit on a qm scale is equivalent to 4 on a graticule scale . So each unit on the qm scale equals 10qm, each unit on the graticule equals 10/4 which is 2.5
How can you calculate the scale for different objective lenses
. Dividing the differences in magnification Eg if an objective lens magnifying X40 gives a calibration of 25qm per graticule unit, then an objective lens magnifying X400 which is 10 times more, gives a calibration of 25/10 which is 2.5qm.