To find the diameter of a wire with the help of screw gauge

Q.3 Write necessary material and procedures for the conduct of following practicals:
i. To find the diameter of a wire with the help of screw gauge.

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 b) Zero Error This error occurs if we move the screw in one direction and then in opposite directions repeatedly. If on bringing the flat end of the screw in contact with the zero mark on base line of the main scale, the instrument is said to be free from zero error. Otherwise an error is said to be there. This can be both positive and negative zero error. 

Apparatus

Micrometer screw gauge, small sphere, fine wire, and half-meter rod. 

Procedure 

1. Find the pitch and least count of screw gauge. 
2. Find the zero error, and determine the sign of screw gauge. 
3. Place the wire in gap AB (see the fig.) and turn the screw gauge till the wire is gently pressed. Note the reading of linear as well as the circular scale in table. 
4. Complete the table up to last column. Take the reading from different places of the wire. 
5. Repeat the process for the given small sphere. 
6. Calculate mean diameter of the sphere. 
7. Find the radius and hence area of cross-section of wire. Also the volume of the sphere by applying the formula

ii. Staining of check cells.

Answer:

Observing human cheek cells under a microscope is a simple way to quickly view and learn about human cell structure. Many educational facilities use the procedure as an experiment for students to explore the principles of microscopy and the identification of cells, and viewing cheek cells is one of the most common school experiments used to teach students how to operate light microscopes. The observation uses a wet mount process that is straightforward to achieve by following an effective preparation method. You can replicate the observational experiment at home or in the classroom with any standard light microscope with magnification settings of X-40 and X-100.

How to Prepare a Wet Mount of Cheek Cells

Before starting, it is always important to ensure that the working surface is clean and that you are wearing a pair of clean gloves to avoid contamination.

Cheek cells can be easily obtained by gently scraping the inside of the mouth using a clean, sterile cotton swab.

Once the cells have been obtained, the following procedure is used for cheek cell wet mount preparation:

1. Physiological saline on a clean microscopic slide (central part of the slide)
2. Smear the cotton swab on to the center (part containing the saline drop) of the clean slide for about 4 seconds to get the cells on to the center of the slide
3. Add a drop of methylene blue solution on to the smear and gently place a cover slip on top (to cover the stain and the cells)
4. Any excess solution can be removed by touching one side of the slide with a paper towel or blotting paper.
5. Place the slide on the microscope for observation using 4 x or 10 x objective to find the cells
6. Once the cells have been found, they can then be viewed at higher magnification

Note- Used cotton swabs and cotton towel should be safely discarded in the trash and not left lying on the working table.

Why do we have to Stain the Cells?

The cell has different parts, and those that can absorb stains or dyes are referred to as chromatic. Having absorbed the stain, these parts of the cell become more visible under the microscope and can therefore be easily distinguished from other parts of the same cell.

Without stains, cells would appear to be almost transparent, making it difficult to differentiate its parts.

Methylene blue has a string affinity for both DNA and RNA. When it comes in contact with the two, a darker stain is produced and can be viewed under the microscope.

The nucleus at the central part of the cheek cell contains DNA. When a drop of methylene blue is introduced, the nucleus is stained, which makes it stand out and be clearly seen under the microscope. Although the entire cell appears light blue in color, the nucleus at the central part of the cell is much darker, which allows it to be identified.

Observation

On mounting the wet slide, the following will be observed:

• Large irregularly shaped cells with distinct cell walls.
• A distinct nucleus at the central part of each individual cell (dark blue in color).
• A lightly stained cytoplasm in each cell. Conclusion

This is an easy and fun experiment that will show kids the basic structure of a cell and its major parts. For easy identification of the parts, the parent or teacher can first show the kids some samples of the cells in advance.This will help them identify different parts with ease.

Once this has been achieved, kids can move on to the next stage of learning the functions of these different parts.