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Multiple choice question for engineering

Set 1

1. In a RADAR system the transmitter of the radar is more sensitive than the receiver.
a) True
b) False

View Answer

Answer: b [Reason:] The basic operation of RADAR is that the transmitter sends out a signal, which is partially reflected by the distant target, and then detected by a sensitive receiver. Because of the presence of noise in the received signal, the receiver has to be more sensitive.

2. For radar system, antennas with a large beam width are preferred over narrow beam antennas.
a) True
b) False

View Answer

Answer: b [Reason:] If a narrow beam width antenna is used in radar, the target’s direction can be accurately given by the angular position of the antenna. Hence narrow beam antennas give more accurate position of the objects.

3. The radar in which both transmission and reception is done using the same antenna are called:
a) Monostatic radar
b) Bistatic radar
c) Monopole radar
d) Dipole radar

View Answer

Answer: a [Reason:] Radar transmits electromagnetic waves and receives the waves that are reflected by objects. If a single antenna is used both for transmission and reception of the signals, they are called monostatic radar.

4. For applications like missile fire control, bistatic radars are used.
a) True
b) False

View Answer

Answer: a [Reason:] In missile fire control, the target is illuminated with one antenna and the reflected wave is received from another antenna in the radar. In situations where continuous transmission and reception of signals is required, bistatic radars are used.

5. When a power Pt is transmitted by an antenna, amount of energy incident on the target is given by the expression:
a) Pt×G/4πR2
b) Pt/4πR2
c) Pt×4 πR2/G
d) None of the mentioned

View Answer

Answer: a [Reason:] The amount of energy incident on the target is proportional to the energy radiated; gain of the antenna G, and R is the distance of the target from the radar system. As the distance from the radar system, the energy incident on the target reduces.

6. The term radar cross section defines the:
a) Scattering ability of the target
b) Power radiating ability of the radar
c) Amount of energy scattered by unwanted objects
d) Cross section of radar area through which energy is emitted

View Answer

Answer: a [Reason:] Radar cross section is defined as the ratio of scattered power in a given direction to the power incident on it. The power incident is the energy radiated by the transmitting antenna of the radar.

7. A ________ determines the target range by measuring the round trip time of a pulsed microwave signal.
a) Pulse radar
b) Doppler radar
c) Cross section radar
d) None of the mentioned

View Answer

Answer: a [Reason:] The working principle of pulse radar is that continuous pulses are transmitted and time is recorded until the pulse is received back by the radar. Based on this delay recorded, the range of target is estimated.

8. Construction of pulse radar is much simpler than a Doppler radar.
a) True
b) False

View Answer

Answer: b [Reason:] In Doppler radar the power / signal is continuously radiated by the transmitting antenna. In pulse radar, pulses are transmitted to the target. Generation and transmission of pulses is more complex as compared to continuous signal.

9. In military applications the radar cross sections of vehicles is minimized.
a) True
b) False

View Answer

Answer: a [Reason:] In military applications the radar cross sections of vehicles is minimized so that the military vehicles remain undetected. Lower the radar cross section, lower is the power scattered, and hence the object remains undetected.

10. Pulse radar operating at 10GHz frequency has an antenna with a gain of 28 dB and a transmitted power of 2kW. If it is desired to detect a target of cross section 12m2, and the minimum detectable signal is -90 dBm, the maximum range of the radar is:
a) 8114 m
b) 2348 m
c) 1256 m
d) 4563 m

View Answer

Answer: a [Reason:] The maximum range of a radar system is given the expression, [PtG2σλ22/ (4π) Pmin] 0.25. Pt is the transmitted power, σ is the radar cross section, G is the antenna gain. Substituting the given values in the above equation, the maximum range of the radar is 8114 m.

Set 2

1. Process annealing is applied to which kind of materials?
a) Steel castings
b) Low carbon steels
c) High carbon steels
d) Medium carbon steels

View Answer

Answer: b [Reason:] Process annealing is a method used to soften and increase the ductility of a previously strain-hardened metal. It is mainly used in case of steel wires and sheet products, especially low carbon steels.

2. For process annealing, the steel is heated at a temperature range of _________
a) 550-650oC
b) 723-910oC
c) 723-1138oC
d) 750-800oC

View Answer

Answer: a [Reason:] In process annealing, the low carbon steels are heated to a temperature slightly below the A1 line, which ranges between 550oC and 650oC. Full annealing is carried out at 723-910oC (hypoeutectoid) or 723-1138oC (hypereutectoid).

3. Which among the following is not applicable to process annealing of steels?
a) Low scaling
b) Rapid
c) Expensive
d) Single phase morphology

View Answer

Answer: c [Reason:] Process annealed steels are heated around 550-650oC, held for some time for softening, then cooled at any desired rate. This process induces single phase morphology. This process is cheaper, more rapid, and produces less scaling as the material is not heated at a high temperature like for full annealing.

4. What happens when internal residual stresses are not removed?
a) Coarse structure
b) Reduction of grain size
c) Distortion
d) Recrystallization

View Answer

Answer: c [Reason:] When internal residual stresses are not removed, distortion or warpage of the material may occur. In order to remove these stresses, stress relief annealing is carried out.

5. Subcritical annealing is another name for ____________
a) Process annealing
b) Stress relief annealing
c) Recrystallization annealing
d) Spheroidise annealing

View Answer

Answer: a [Reason:] Process annealed steels are heated around 550-650oC, held for some time for softening, then cooled at any desired rate. This process induces single phase morphology. This process is otherwise known as subcritical annealing.

6. Commercial annealing is another name for ____________
a) Process annealing
b) Stress relief annealing
c) Recrystallization annealing
d) Spheroidise annealing

View Answer

Answer: b [Reason:] When internal residual stresses are not removed, distortion or warpage of the material may occur. Stress relief annealing is carried out to remove these stresses caused by castings, quenching, machining, welding etc. Stress relief annealing is otherwise also known as commercial annealing.

7. Removal of internal residual stresses at low temperatures is known as ________
a) Recrystallization
b) Recovery
c) Morphology
d) Phase transformation

View Answer

Answer: b [Reason:] Recovery is a low-temperature phenomenon used to remove internal residual stresses. This is done with little change in mechanical properties and no major changes in microstructure. Stress relief is also known as recovery.

8. What kind of annealing does this graph illustrate?
tricky-engineering-materials-metallurgy-questions-answers-q8
a) Process annealing
b) Stress relief annealing
c) Recrystallization annealing
d) Spheroidise annealing

View Answer

Answer: d [Reason:] Stress relief annealing is carried out to remove the stresses caused by castings, quenching, machining, welding etc. This can be done by prolonged heating of the material slightly above and below the A1 line. Full annealing occurs above the A1 and A3 lines, whereas process annealing occurs slightly below the A1 line.