Engineering Metrology Questions and Answers – Optical Instruments for Angular Measurement

This set of Engineering Metrology test focuses on “Optical Instruments for Angular Measurement”.

1. Which of the following is not true for autocollimators?
a) Has an infinity telescope
b) Has an autocollimator
c) For smaller angle it is not accurate
d) Very high sensitivity

Explanation: Autocollimator is an optical instrument which is used for the measurement of small angular differences. Autocollimator provides a very sensitive and accurate approach for small angular measurements. Autocollimator is an infinity telescope and a collimator combined into one instrument.

2. What is the relationship between the linear displacement of the graticule image in the eyepiece plane and reflector tilt?
a) Both are independent of each other
b) Linear displacement is directly proportional to the reflector tilt
c) Linear displacement is inversely proportional to the reflector tilt
d) Linear displacement is directly proportional to the square of the reflector tilt

Explanation: Linear displacement of the graticule image is directly proportional to tilt of the reflector. It can be measured by an eyepiece graticule, electronic detector system or optical micrometer, scaled directly in angular units.

3. Up to which accuracy length can be measured by laser interferometer?
a) 1 part in 108
b) 2 part in 108
c) 1 part in 106
d) 2 part in 106

Explanation: It is possible to measure length to accuracy of 1 part in 106 with laser interferometer. With two retro-reflectors that are placed at a fixed distance, and a length measuring laser interferometer the angle change can be measured to an accuracy of 0.1 second.

4. Which of the following option is correct for the given statements about optical instruments for angular measurements?
Statement 1: Laser interferometer with two-retro reflector uses sine principle.
Statement 2: Photoelectric microptic autocollimator can be used as a visual collimator.
a) F, F
b) T, F
c) F, T
d) T, T

Explanation: Laser interferometer uses the Sine principle. The line which joins the poles of the reflectors makes the hypotenuse of the right triangle. Photoelectric collimator can be used as a visual autocollimator and is available with a dark field graticule.

5. Which of the following is true for automatic position sensing autocollimator?
a) Accuracy is affected by normal mains fluctuations
b) There is no effect of lamp ageing on the accuracy of this instrument
c) Instrument measure in all planes simultaneously
d) It is not ideal for the repetitive checking

Explanation: Accuracy of automatic position sensing autocollimator is not affected by lamp ageing or normal mains fluctuations. Automatic autocollimators are ideal for the repetitive checking of the components.
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6. How many pads are included for use under the foot screws in leveling base of autocollimator?
a) 2
b) 3
c) 4
d) 5

Explanation: Three pads are present in the leveling base of autocollimator for use under the foot screws. There is no requirement to remove the autocollimator after use as the autocollimator case is constructed to take both items.

7. What is the main use of steel cube reflector in autocollimator?
a) To provide a 90 degree standard in 3 planes
b) For general bench use
c) Calibrate surface plate
d) For setting but not checking perpendiculars

Explanation: Steel cube reflector can be used as a general purpose reflector. It can be used for providing a 90 degree angle standard in three planes. It can be used for setting or checking perpendiculars.

8. What is the range of readings up to distance of 9 metres in microptic autocollimator?
a) 15 minutes of arc
b) 20 minutes of arc
c) 5 minutes of arc
d) 10 minutes of arc

Explanation: A pair of target wires is used in this instrument. These wires are placed in the focal plane of a collimating lens. It is possible to read the tilt of reflector to normal upto 1/2 sec. of arc with the help of micrometer. The instrument has a range of readings of 10 minutes of arc up to 9 meter distance.

9. Which of the following used moire gratings for angular measurements?
a) Laser interferometer
b) Microptic autocollimator
c) Precision polygons
d) Goniometer

Explanation: Goniometer constitutes the continuously rotating Moire gratings for angular measurements with high accuracy. Two radial gratings are employed in goniometers which are rotating in unison.

10. Which of the following is true for Reading heads present in goniometer?
c) There is only one reading head which is moving with a rotatable work table
d) Two reading heads, one is stationary and other is rotating with work table

Explanation: Two reading heads are present in the goniometer. One head remains stationary while other moving with a rotatable work table. The phase difference between the outputs of heads varies continuously as the second head attached to the rotary table is moved.

11. How much angle accuracy is possible with a goniometer fitted with two 32400 lines radial grating?
a) 0.1 second of arc
b) 1 second of arc
c) 2 second of arc
d) 0.5 second of arc

Explanation: Advantage of goniometer is that grating errors are entirely averaged to zero during the time of measurement thus giving the inherent accuracy. With a goniometer which is fitted with two 32400 lines radial gratings, it is possible to obtain angle measurements to an accuracy of 0.1 second of arc.

12. Which of the following is not true for angle dekkor?
a) It is a type of autocollimator
b) It can be used as a comparator
c) It is a more precise instrument than autocollimator
d) It has a wide field of application without the operation of a micrometer

Explanation: It is a type of collimator and contains a small illuminated scale. The instrument measures by comparing the readings obtained from a standard. This is less precise instrument than autocollimator but it has wide field of application for general angular measurement.

13. What is the alternate name of constant deviation prism?
a) Optical square
b) Dowell prism
c) Circular prism
d) Reflector prism

Explanation: Constant deviation prism is also known as optical square. The special property of optical square is that it always reflects the ray through the same angle, which means doesn’t depend on the angle of incident.

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