# Surveying Questions and Answers – EDM – Electromagnetic Waves

This set of Surveying Multiple Choice Questions & Answers (MCQs) focuses on “EDM – Electromagnetic Waves”.

1. Modern EDM uses which among the following waves?
a) Visible rays
b) Thermal infra-red
c) Modulated infra-red

Explanation: Modern EDM uses the modulated infra-red waves, which are capable of receiving the reflected waves from a distance of 100km.

2. Which property of an electromagnetic wave, depends on the medium in which it is travelling?
a) Velocity
b) Frequency
c) Time period
d) Wave length

Explanation: The frequency, wavelength and time period can all vary according to the wave producing source. But, the velocity of an electromagnetic wave depends upon the medium through which it is travelling. The velocity of wave in a vacuum is termed as speed of light, which is assumed to be 3 x 108 m/s.

3. The distance in EDM is measured by______________
a) Frequency of the wave
b) Wave length
c) Phase difference
d) Amplitude

Explanation: In general, the various EDM systems available do not measure the transit time directly. The distance is determined by measuring the phase difference between the transmitted and reflected signals, which possible only when the process is done without errors.

4. Tellurometer, a type of EDM uses which of the following waves?
a) Visible rays
b) Infra-red waves
c) Micro waves

Explanation: Tellurometer is generally having a range of 100km i.e., it is capable of measuring distance up to 100km. In order to function properly it requires a high range propagating wave, which can reflect back to the instrument.

5. Find the value of D if the wave length of the wave is 40m, n=2 m and the angles are given as θ1 = 0˚, θ2 = 180˚.
a) 50m
b) 40m
c) 20m
d) 10m

Explanation: The value of D can be found by,
2D = n*λ + Δ*λ. On substitution, we get
2D = 40*(2 + (180-0/360))
D = 50 m.
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6. Electromagnetic waves are represented in which of the following format?
a) Longitudinal waves
b) Transverse waves
c) Sinusoidal waves
d) Surface waves

Explanation: A sinusoidal wave describes the oscillation periodically. Since the electromagnetic wave is represented in the form of sine curve it is named after it as sinusoidal wave.

7. For increasing accuracy, high frequency of propagation is used.
a) True
b) False

Explanation: In order to increase accuracy, it is recommended to use an extremely high frequency of propagation. However, the available phase comparison techniques cannot be used at frequencies greater than 5* Hz, which corresponds to a wavelength of 0.6 m.

8. What would be the value of length if the distance is given as 30m, m= 3 and the change in length is 8m.
a) 7.43m
b) 7.34m
c) 6.34m
d) 5.43m

Explanation: The value of length can be found out by using the formula,
D = m*l + Δ l. On substitution, we get
30 = 3*l + 8
L = 7.34 m.

9. Phase difference can be expressed in which of the following format?
a) Meters per second
b) Meters
c) Cycles
d) Seconds

Explanation: In the total station, the distance between two point scan be determined by measuring the phase difference between transmitted and reflected signals. Phase difference can be expressed in terms of the fraction of cycles, which provides the best output for quick calculation and for easy understanding.

10. Which of the following represents the correct sequence for the basis of EDM propagation?
a) Propagation, generation, reflection and reception
b) Generation, reception, reflection and propagation
c) Generation, propagation, reception and reflection
d) Generation, propagation, reflection and reception

Explanation: Electronic Distance Measurement method is based on generation, propagation, reflection and subsequent reception of electromagnetic waves. The type of electromagnetic waves generated depends on many factors but mainly, on the nature of the electrical signal used to generate the waves. It follows the above-mentioned sequence without any disturbance in it.

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