Question

If the spacing of cross-hairs in a stadia diaphragm of a tachometer is 12 mm and the focal length of the object glass is 24 cm, then multiplying constant of the tachometer is:
1. 20
2. 100
3. 0.005
4. 200

Answer 1

Correct Answer - Option 1 : 20

Distance from instrument location to staff is given by:

D = ks +c

Where, c is the additive constant and k is the multiplying constant.

\(k = \frac{f}{i}\)

c = f + d

where,

i = stadia interval = staff intercept = 12 mm

f = focal length = 24 cm = 240 mm

d = distance of the instrument axis from the centre of the object glass = 190 mm

\(k = \frac{{240}}{12} = 20\)

Multiplying constant of the tachometer is 20