# Mechatronics Questions and Answers – Motion Sensors

This set of Mechatronics Multiple Choice Questions & Answers (MCQs) focuses on “Motion Sensors”.

1. Which type of lens is generally used in the PIR sensors?
a) Concave lens
b) Convex lens
c) Bifocal lens
d) Fresnel Lens

Explanation: Fresnel lens is most commonly used lens in the PIR sensors. These Lens help to evenly distribute the Passive Infrared waves around it which facilitates it to detect motion in 180 degrees in all X,Y and Z axis.

2. The Samuel motion sensor works on which principle?
a) Hall effect
b) Inductive effect
c) Doppler effect
d) Capacitive Effect

Explanation: The Samuel motion sensor works on the principle of “Doppler Effect”. It states that, it is the change in the frequency of light, sound or any other wave in relation to observer who is in motion with respect to wave source.

3. Tomographic sensors uses which type of waves for motion detection?
b) Ultrasonic waves
c) Infrared waves
d) Microwaves

Explanation: Tomographic sensors uses radio-waves for motion detection. They can sense objects when those radio waves are disrupted. They are generally very costly and are mostly used in the industrial areas.

4. Combined motion sensors are triggered when all the motion sensors detect a motion.
a) True
b) False

Explanation: The Combined motion sensors are triggered when all the motion sensors detect a motion. If any one of the sensor detect motion then the alarm is not triggered. This facility eliminates the possibility of fake alarms.

5. Microwave motion sensors has more area coverage than the PIR sensors.
a) True
b) False

Explanation: Microwave motion sensors have larger area of coverage than that of the Passive Infrared sensors as it uses Microwaves for the detection of the objects. They are usually more expensive than the PIR sensors.

6. What is the frequency range of the ultrasonic sound waves used by the ultrasonic sensors?
a) 20000Hz to 25000Hz
b) 25KHz to 50KHz
c) 25Hz to 55Hz
d) 25Hz to 50Hz

Explanation: The Ultrasonic Sensors produces sound waves of frequency in the range of 25KHz to 50KHz. These Ultrasonic sounds produced by the sensors transmitter bounce back the in the same path when it encounters an object in its path. The receiver part receives these waves and calculates the distance and displacement accordingly.

7. PIR stands for ____
a) Passive Infrared
b) Pulsating Infrared
c) Pulsating ratio
d) Pulse is radiation

Explanation: PIR stands for Passive infrared. The PIR sensors are most commonly used motion sensors that are used for detecting motion by recognizing the heat sensors. They are designed to detect body heat and for motion recognition.

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8. RCWL- 0516 is an example of which type of sensor?
a) Infrared Sensor
b) Microwave Radar Sensor
c) Ultrasonic Sensor
d) Temperature Sensor

Explanation: RCWL- 0516 is an example of Microwave radar sensor. It is used as an alternative to the PIR sensors. They are cheap and more accurate. Due to the usage of the microwaves, they have a greater range of detecting objects.

9. The distance range of detection of the PIR sensor is ________
a) 5-10 cm
b) 5-7 m
c) Up to 12 m
d) 5-12 cm

Explanation: The range of detection of the PIR sensor is up to 12 meter. They can accurately detect objects in motion in this range. These sensors constitute of a pyroelectric sensors that can detect different levels of infrared radiation.

10. “SAW” in respect to acoustic wave technology stands for ______
a) Sound Acoustic Wave
b) Surface Acoustic Wave
c) Simple Acoustic Wave
d) Surface Acoustic Wave

Explanation: “SAW” in respect to acoustic wave technology stands for Surface Acoustic Wave. This wave is used in the acoustic sensor for detection of motion. It is named so because acoustic wave has to propagate through a surface as a medium, any change in the propagation path, changes the velocity and other property of wave which is used to detect motion in these acoustic sensors.

11. A car moves with a speed of 30 km/hr. What will be the speed of the same car measured by a speed sensor which is placed in a truck which is moving with a speed of 20 km/hr in the same direction?
a) 30 km/hr
b) 50 km/hr
c) 10 km/hr
d) 0 km/hr

Explanation: Speed of the same car measured by a speed sensor which is placed in a truck will be 10 km/hr. Since both car and the truck moves in the same direction therefore the relative velocity of the car will be 30–20=>10km/hr.

12. A moving platform moves with a speed of 100 km/hr. What will be the speed of a boy who is running on it with a speed of 10 km/hr along the motion of the moving track measured by a speed sensor placed on stationary ground?
a) 150 km/hr
b) 160 km/hr
c) 110 km/hr
d) 140 km/hr

Explanation: Speed of the boy measured by a speed sensor who is running on the moving platform will be 110 km/hr. Since both move in the same direction then the speed of the boy gets added up with the speed of the moving platform therefore net speed becomes 100+10=110.

13. A car moves with a speed of 60 km/hr. What will be the speed of the same car measured by a speed sensor which is placed in a bicycle which is moving with a speed of 12 km/hr in the opposite direction?
a) 60 km/hr
b) 72 km/hr
c) 58 km/hr
d) 48 km/hr

Explanation: Speed of the same car measured by a speed sensor which is placed in a bicycle will be 72 km/hr. Since both car and the truck moves in the opposite direction therefore the relative velocity of the car with respect to bicycle will be 60+12=>72km/hr.

14. A moving platform moves with a speed of 80 km/hr. What will be the speed of a boy who is running on it with a speed of 20 km/hr opposite to the motion of the moving track measured by a speed sensor placed on stationary ground?
a) 50 km/hr
b) 60 km/hr
c) 100 km/hr
d) 160 km/hr

Explanation: Speed of the boy measured by a speed sensor who is running on the moving platform will be 60 km/hr. Since the boy and the moving platform moves in opposite direction then the speed of the boy gets subtracted with the speed of the moving platform therefore net speed becomes 80-20=60.

15. A car moves with a speed of 50 km/hr. What will be the speed of a stationary bicycle parked along the roadside measured by a speed sensor which is placed in the same car?
a) 50 km/hr
b) 60 km/hr
c) 0 km/hr
d) 40 km/hr

Explanation: speed of a stationary bicycle measured by a speed sensor will be 50 km/hr. Since car is moving with a speed of 50 km/hr therefore relative speed of the bicycle with respect to car will be 50–0=50 km/hr.

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