| Aim | Measuring the Thickness of a Sheet Using a Screw Gauge |
| Apparatus Required | Sheet whose thickness is to be measured Screw gauge Vernier scale Flat surface Paper or cloth for cleaning the screw gauge |
| Theory | The screw gauge is a precision measuring instrument that is commonly used to measure the thickness of small objects. The screw gauge works by using a calibrated screw that moves a spindle and jaws towards each other. The spindle is attached to a thimble that can be rotated, while the jaws are used to hold the object being measured. The screw gauge consists of two scales: the main scale and the Vernier scale. The main scale has evenly spaced markings, while the Vernier scale has slightly different markings that allow for more precise readings. The Vernier scale is a sliding scale that is used to read the fractions of a division on the main scale. The measurement of thickness using a screw gauge involves placing the object being measured between the jaws of the screw gauge and rotating the thimble until the jaws touch the object. The measurement is then obtained by reading the main scale and the Vernier scale. The main scale reading is obtained by counting the number of divisions on the main scale that are visible to the left of the zero mark. The Vernier scale reading is obtained by noting the division on the Vernier scale that coincides with a division on the main scale. The measurement obtained is then calculated using the formula: Thickness = Main scale reading + (Vernier scale reading x Least count). The least count of the screw gauge is the smallest measurement that can be read on the instrument. The least count is calculated by dividing the pitch of the screw by the number of divisions on the Vernier scale. The pitch of the screw is the distance travelled by the screw for one complete rotation. The accuracy of the measurement using a screw gauge depends on the least count of the instrument and the ability of the person taking the measurement. To ensure accuracy, it is important to take multiple measurements and calculate the average. It is also important to ensure that the screw gauge is clean and free from any debris, and that the object being measured is held firmly and is not at an angle. In conclusion, the screw gauge is a precision measuring instrument that is commonly used to measure the thickness of small objects. The measurement obtained using a screw gauge depends on the least count of the instrument and the ability of the person taking the measurement. By following the correct procedure and taking appropriate precautions, accurate measurements can be obtained using a screw gauge. |
| Procedure | Ensure that the screw gauge is clean and free from any dust or debris. Place the sheet whose thickness is to be measured on a flat surface. Open the jaws of the screw gauge by rotating the thimble until the two jaws are slightly apart. Place the jaws of the screw gauge on the sheet, ensuring that they are held firmly and are not at an angle. Rotate the thimble clockwise until the jaws of the screw gauge are just touching the sheet. Look at the Vernier scale and note the number of divisions that are visible to the left of the zero mark. Determine the main scale reading by noting the number of millimeter divisions on the main scale that are visible to the left of the zero mark. Determine the Vernier scale reading by noting the division on the Vernier scale that coincides with a division on the main scale. Add the main scale reading and the Vernier scale reading to obtain the measurement of the sheet’s thickness. Repeat the measurement two or three times to ensure accuracy and record the average of the readings. |
| Observation | Observations: The screw gauge has two jaws that move towards each other when the thimble is rotated. The Vernier scale on the screw gauge has 10 divisions that correspond to 9 divisions on the main scale. The Vernier scale allows for measurements to be taken with a greater degree of accuracy than would be possible with just the main scale. |
| Calculations | The thickness of the sheet can be calculated using the formula: Thickness = Main scale reading + (Vernier scale reading x Least coun The least count of the screw gauge can be calculated using the formula: Least count = Pitch / Number of divisions on the Vernier scale where Pitch is the distance travelled by the screw for one complete rotation and is usually equal to 1 mm. The accuracy of the measurement can be calculated by dividing the least count of the screw gauge by the measurement obtained and multiplying by 100%. Conclusion: By following the above procedure and precautions, the thickness of a sheet can be accurately measured using a screw gauge. The accuracy of the measurement can be improved by taking multiple readings and calculating the average. The screw gauge provides a greater degree of accuracy than would be possible with just the main scale. |
