This set of Engineering Drawing Multiple Choice Questions & Answers (MCQs) focuses on “Types of Scales – 4”.
1. Which of the following statement is incorrect with regard to plain scales?
a) Plain scales represent two units
b) Zero should be placed between the units and its subdivisions
c) The representative factor should be mentioned below the scale
d) It can read up to three decimal places
Explanation: Plane scales measure a unit and its subunits so it can represent only the first decimal place of measurement. In the construction of plain scales, all units are placed to the right side of the zero, which is called as the main scale and to the left of zero, sub-divisions of units are placed.
2. The relation between main scale division (M.S.D) and Vernier scale division (V.S.D) for backward Vernier scale is _______
a) n*V.S.D = (n-2)*M.S.D
b) n*M.S.D = (n-1)*V.S.D
c) n*M.S.D = (n-2)*V.S.D
d) n*V.S.D = (n+1)*M.S.D
Explanation: In Vernier scale, (n+1) or (n-1) divisions on the main scale are divided into n divisions in Vernier scale. If it is (n+1) M.S.D. it is called as backward Vernier and if it is (n-1) it is called as forward Vernier.
3. How do we calculate least count (L.C) for a forward Vernier?
a) L.C = 1V.S.D – 1M.S.D
b) L.C = (V.S.D/n)
c) L.C = M.S.D/(n+1)
d) L.C = V.S.D/(n-1)
Explanation: In forward Vernier, for nV.S.D we have (n-1) M.S.D and the least count (L.C) or the Vernier constant (V.C) is equal to (1 M.S.D -1 V.S.D), as nV.S.D = (n-1) M.S.D. Hence replacing M.S.D with nV.S.D/(n-1) . We get L.C= V.S.D/(n-1).
4. Diagonal scales can only measure the first decimal place of measurement.
Explanation: Diagonal scales can measure even minute distances accurately to three decimal places. This is achieved through the principle of diagonal scale, using the principle of similar triangles, sub-divisions are again divided into the number of equal parts.
5. Put the statements in an order to divide the line AB into 10 parts using the principle of diagonal scales.
i. Number the division-points as 1, 2, 3, up to 9 starting from C and later join AC.
ii. Divide the line BC into 10 equal parts.
iii. Draw a perpendicular line BC TO the line AB.
iv. Hence 9’9 is 0.9AB and similarly, other 2’2 is 0.2AB.
v. Number the cutting points on AC as 1’, 2’, 3’ and so on up to 9’.
vi. Draw lines parallel to AB through the division-points.
a) i, iv, v, ii, vi, iii
b) i, v, vi, ii, iv, iii
c) iii, ii, i, vi, v, iv
d) i, ii, iii, iv, v, vi
Explanation: In the principle of the diagonal scale we apply the concept of similar triangles. So, we need to draw a perpendicular to B, say BC and form a right angle triangle ABC. By dividing the line BC into 10 equal parts (required number of parts as mentioned in the question) and drawing lines parallel to AB through division points, all these lines give the measurement as 0.1AB, 0.2 AB, 0.3AB, 0.4AB and so on up to 0.9AB.
6. Scales which can read different units and having the same representative fraction is called ________
a) Diagonal scales
b) Vernier scales
c) Comparative scales
d) Plain scales
Explanation: Comparative scales are graduated to read different system of units they have two scales with the same R.F. placed one above the other. They may be plain scales, diagonal scales or Vernier scales.
7. Which of the following is used to measure angles accurately in surveying?
a) Plain scales
b) Diagonal scales
c) Circular Vernier scales
d) Comparative scales
Explanation: Vernier scales may be used as a straight or circular. Circular Verniers are used in surveying are called Theodolite which measures angles between the two points in surveying.
8. How can we decide the minimum length of a scale, when Representative factor (R.F) and the maximum length of measurement (L) are known?
a) Length of scale = R.F+L
b) Length of scale = R.F/L
c) Length of scale = R.F-L
d) Length of scale = R.F*L
Explanation: We can draw the scale as long as possible but the minimum length of scale should be capable of measuring the maximum length of required measurement. We know R.F = (length of the drawing)/(Actual length of the object), Hence length of scale = R.F* maximum length of required measurement.
9. When the value of one Vernier scale division is less than one it is called as forward Vernier.
Explanation: In forward Vernier for every nV.S.D we have (n-1) M.S.D, where the least count of forward Vernier scale is [(n-1)M.S.D/n], which gives a value less than one. Hence the given statement is true.
10. When the length of the line drawn is 2 mm, and the taken representative fraction is 1:2. Find the actual length of the line?
a) 1 mm
b) 0.5 mm
c) 4 mm
d) 3 mm
Explanation: Representative fraction is the ratio of the length of the drawings to actual length, hence actual length = (length of the drawing)/R.F. Here R.F is 1:2 mm and length of the drawing is 2 mm, therefore the actual length of the line is 2*2 mm = 4 mm.
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