| Aim | Measuring the Diameter of a Wire Using a Screw Gauge |
| Apparatus Required | Wire whose diameter is to be measured Screw gauge Vernier scale Flat surface Paper or cloth for cleaning the screw gauge |
| Theory | If the wire is placed between the plane faces A and B and the edge of the cap is located ahead of the Mb division of the linear scale, the linear scale reading (L.S.R.) will be equal to N. If the nth division of the circular scale is aligned with the reference line, the circular scale reading (C.S.R.) will be equal to n multiplied by the least count of the screw gauge (L.C.). The total reading (T.R.) can be calculated as the sum of the L.S.R. and C.S.R., which is equal to N+n x (L.C.). If the mean diameter of the wire is D and the mean length is l, the volume of the wire can be calculated by multiplying pi by the square of the mean diameter and the mean length, which is expressed as V = pi x D^2 x l. |
| Procedure | Ensure that the screw gauge is clean and free from any dust or debris. Place the wire whose diameter 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 wire between the jaws of the screw gauge, ensuring that it is held firmly and is not bent or distorted. Rotate the thimble clockwise until the jaws of the screw gauge are just touching the wire. 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 wire’s diameter. 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 diameter of the wire can be calculated using the formula: Diameter = Main scale reading + (Vernier scale reading x Least count) 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 diameter of a wire 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. |
