**Screw Gauge Viva Questions and Answers**

**(i) Name the instrument used for measuring the thickness of a piece of paper**

Ans: Screw gauge.

**(ii) What is meant by pitch of a screw gauge?**

Ans: It is the distance advanced by the screw for one complete rotation of the head.

**(iii) The pitch of a screw is 1 mm and the number of divisions on the head scale is 100. What is the least count?**

Ans: Least count = pitch/ No: of divisions on the head scale = 1/100 = 0.01 mm

**(iv) What is zero error of a screw gauge?**

Ans: If the zero of the head scale does not coincide with the zero of the pitch scale when the end of the movable screw is in contact with the stud, the screw gauge is said to have zero error.

**(v) If the zero of the head scale is 5 divisions above the line of graduation of the pitch scale when the gap is closed, what is the zero error? What is the zero correction? Least count of the vernier = 0.01 mm**

Ans: zero error = -5 x 0.01 = -0.05 mm and zero correction = +0.05 mm

**(vi) If the zero of the head scale is 5 divisions below the line of graduation of the pitch scale when the gap is closed, what is the zero error and correction? Least count = 0.01 mm**

Ans: zero error = +5 x 0.01 = +0.05 mm and zero correction = -0.05 mm

**(vii) Why do we take a number of observations for the diameter of a wire?**

Ans: Even if the wire appears uniform it may not be true. So to take the average value we take a set of readings

**(viii) Why do you stop rotating the screw as soon as the ratchet begins to turn between the fingers?**

Ans: When the ratchet begins to turn, the two faces are in contact or in contact with the body held between them. The device avoids undue pressure on the screw.

**(ix). Another name of screw gauge.**

Micrometer

**(x). What is the principle of screw gauge?**

The linear distance moved by screw is directly proportional to the rotation given to the head. This is the principle of the micrometer screw.

**(xi). Why is screw gauge so named?**

Screw gauge is generally used to measure the diameter of wires which are governed by some standard numbers called standard wire gauge. As the screw gauge makes use of a screw for such measurements, it is named screw gauge.

**(xii). What is zero error of the screw gauge?**

When the screw tip is in contact with the stud and the zero line of the head scale does not coincide with the reference line of the pitch scale, there is zero error.

**(xiii). What is the basic function of a ratchet?**

It prevents the screw being pressed too hard or too son against the object

**(xiv). Define pitch of the screw gauge**

The pitch of the %mu gauge is the distance moved by the screw for one complete rotation of the head scale.

Pitch = Distance moved /Number of rotations

**(xv). A screw gauge has 100 divisions on its head scale and the pitch of the screw is 1 mm. What is its least count?**

Least count = 1mm/100 = 0.01mm

**(xvi) Aim of Screw Gauge Experiment**

Ans: To find

(a) the diameter of a wire and

(b) thickness of an irregular glass plate using screw gauge and find their volumes.

**(xvii) Theory of Screw Gauge Experiment**

Ans: Dimension measured = P.S.R + fraction = P.S.R + (H.S.R x L.C);

where P. S . R = Pitch Scale Reading,

H.S.R = Head Scale Reading

and L.C = Least count of the screw gauge

Volume of the wire = πr^{2}l; where r = radius of the wire and l = length of the wire

**(xviii) How to find the pitch of the screw?**

Ans: Pitch = Distance moved/Number of rotations

**(xix) How to find the least count of the screw gauge?**

Ans: The least count of the screw is the distance moved by it when it is rotated through one division of the head scale.

Least count = Pitch/No: of divisions on the head scale.

**(xx) How to find the zero correction?**

Ans: The screw is turned till the tip touches the stud. If the zero division does not coincide with zero of the pitch scale, then it is zero error. So a correction has to be applied. If it is not screwed, there is no zero correction. If it is over screwed, the zero correction is positive (+3 divisions). If it is under screwed, the zero correction is negative (-2 divisions).

**(xxi) How to find the diameter and volume of the wire?**

Ans: Diameter of the wire = P.S.R + fraction = P.S.R+ (corrected H.S.R. x L.C)

Volume (V) of the wire is calculated using the equation, V = πr^{2}l

**(xxii) How to find the thickness and volume of the glass plate?**

Ans: The given glass plate is griped between the tip of the screw and the stud. The P.S.R and the H.S.R are noted as before. The thickness of the glass plate is

t = P.S.R + (corrected H.S.R) x LC

The glass plate is placed over a graph paper and its outline is traced on the graph paper. The area A of the glass plate is taken from the graph paper. The volume of the glass plate is calculated from the equation.

V = A x t