[Physics Class Notes] on Measure Diameter of Given Wire Using Screw Gauge Pdf for Exam

A screw gauge can be described as an object which is used to measure cylindrical and spherical objects. It gives precise measurements but can be a bit difficult to use. In technical terms, the screw gauge can be defined as a mechanical tool that facilitates the measurement of diameter, radius, or thickness of a thin metal sheet, or the thickness of a wire with maximum accuracy. 

A screw gauge is an instrument that measures the diameter of thin objects like a wire. The name screw gauge is provided because it is most commonly used to measure the diameters of wire which in turn are governed by the standard numbers that are called the standard wire gauge.

A screw gauge also measures the thickness of small sheets such as glass and plastic.

Since a screw gauge works on the principle of a micrometer, that’s why we call it the principle of a micrometer screw.

Screw Gauge

When accurately cut, a single threaded screw is placed inside a closely fitted nut and rotated. The two types of motions occur, one is circular and the other is a linear motion of the screw along its axis.

The distance moved by the screw in one complete rotation of the screw equals the distance between the two consecutive threads of the screw gauge. This distance is called ‘Pitch’ and it is always a constant value.

Since the linear motion (the small distances) made by the screw gauge is hard to be measured, these linear distances are amplified into larger distances by the rotational motion of the screw. These rotations are easily measurable. The screw gauge is constructed in a way that follows the principle of ‘micrometer screw.’

Now, to measure the diameter of a given wire using a screw gauge, we need to know its structure.

Structure of a Screw Gauge

The screw gauge consists of a screwed spindle which is fitted with a U-shaped frame and is attached to the thimble. A graduated scale in mm is engraved parallelly over the axis of the thimble. To the head of the screw, a sleeve is attached. 

There is a racket that is present at the head of the screw which avoids undue tightening of the screw. The circular scale which is present on the thimble is known as the head scale which is divided into 50 or 100 equal parts. The sleeves start moving over the pitch scale when the screw is worked. ‘Anvil’ is a stud that is fixed on the ‘U’ frame with a plane-ended surface. It is exactly opposite to the tip of the screw. The zero of the head scale coincides with the zero of the pitch scale when the top of the screw comes in contact with the anvil.

Determine the Diameter of Wire Using Screw Gauge

Pitch

Aim- To measure the diameter of a given wire by using a screw gauge

Apparatus- wire, screw-gauge, magnifying lens, half-meter scale

Procedure- 

1. Observe the value of one linear scale division (LSD).

2. Find the pitch and the least count of the screw gauge step-wise.

3. The plane face B and the plane face A are brought into contact and see if there is any zero error. This is to be done thrice and if there is no zero error, then record the zero error nil.

4. Now, face B and face A is moved away and the wire is length-wise placed over face A and face B is moved towards face A by using the ratchet head R. Stop is R is turning without moving the screw.

5. After this, the number of visible divisions of the linear scale is noted and these divisions should be uncovered by the edge of the cap. This reading IV is called the LSR or the linear scale reading.

6. Now, the number of divisions of the circular scale n which are lying over the reference line is noted. 

7. Now the steps 5 and 6 are repeated after the wire is rotated by 90° to measure the diameter in the perpendicular direction. 

8. Now the steps 4,5,6, and 7 are repeated for five different positions which are separated equally on the length of wire. Each of the observations is recorded in a tabular form.

9. Now, the total reading is calculated and zero correction is applied in each case.

10. Mean of different values of diameter is taken.

11. After stretching the wire along a half-meter scale, the length of the wire is measured. Now, one end of the wire is kept at a known mark and the position of the other end is noted. The length of the wire is the difference between the two ends of the wire. This is done thrice and recorded.

To Determine the Diameter of A Wire By Screw Gauge

Firstly, we count the number of divisions on the linear scale on a place completely uncovered by the cap. Let’s suppose that we got the reading as 4.0 mm as a linear scale reading.

Now, we rotate the screw 3 times till the zero mark of the head scale reaches the reference line, it means one rotation is complete.

After four rotations, we note the reading and it comes out 6.0 mm. We got the linear distance mode as:   7.0 mm –  4.0 mm  = 3.0 mm.

So, the pitch can be calculated as:

=[frac{Linear distance moved by a screw}{one rotation of the screw}]=[frac{3mm}{3}]

= 1 mm

So, the pitch of the screw is 1 mm or 0.1 cm.

So, the distance moved by the screw in one complete rotation of the circular cap is 1 mm.

Least Count of the Screw Gauge

A circular cap has 100 divisions, if the cap moves one division, then the distance moved is 1/100 of the pitch, which is the least count of the screw gauge.

So, the formula for the least count is:

L.C.=[frac{Pitch}{No of Division in a circular/head scale}]=[frac{1}{100}]

= 0.01 mm or 0.001 cm.

Zero error reading:

1.  …… mm

2. ……..mm

3. ……..mm

Mean zero error…….mm.

The table used in the calculation

Formulas Used

Length of the wire, l= (i) ……cm, (ii)……cm, (iii)……cm.

Mean Diameter of the wire,

D=[frac{D_1(a)+D_1(b)+…+D_3(a)+D_3(b)}{6}=….mm+….cm]

Mean length of the wire,

l=[frac{l_1+l_2+l_3}{3}=….cm]

Volume of the wire,

V=[pi (frac{D}{2})^2l=….cm^3]

Conclusion

This is all about how a screw gauge can be used for measuring the diameter of a given wire. There is a list of precautions that need to be taken care of to get the right values. Focus on the process and learn how to use it to measure the diameter of small objects.