1. The trigger time for an SCR with a capacitor at its gate ranges from a) O deg
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1. The trigger time for an SCR with a capacitor at its gate ranges from a) O deg to 45 deg b) 0 deg to 90 deg c) O deg to 180 deg d) 180 deg to 360 deg The major disadvantage of using a photoelectric sensor using the opposed sensing method is a) Cannot detect transparent objects b) Not good for small object detection c) Short sensing distance d) All of the above 2. 3. For measuring level from 0 to 4 meters in a tank, it is installed some ultrasound device consisting of a transmitter and a receiver, and installed at the 4 m level. It was send a testing signal, received 20 msec latter. Take the sound speed in the air as 340 m/sec. The water level in the tank is: a) 0.6m b) 3.4 m c) 2.3 m d) 1.7 mO Assuming the values of all resistors connected to a difference op-amp are the same, what is the output voltage when +3 V is applied to the inverting input and +1 V is applied to the noninverting input a) +1 V b) +2 V c) +4 V d) -2V 4.Explanation / Answer
Ans 1) Option C: 0-180 deg.
This is the problem of RC firing circuit where the firing angle can be varied from 0-180 degree unlike resistor firing circuit where we can go upto 90 degree only.
Ans 2) Option A: can not detect transparent object.
as in opposed sensing method the emitter and receiver are positioned opposite to each other so that the sensing energy of emitter is directly aimed to receiver(hence maximum energy is reached so its range is maximum) and object is detected when it interrupt the sensing path between two object so in case of tranparent object there is no interruption so we can't use it to detect transparent object
Ans 3) Option A: 0.6 m.
as distance of the water surface from the sensor is, distance= (speed*time)/2 = (340*20*10^-3)/2 = 3.4m
as sensor is installed at 4m height so water level in the tank is = 4m -3.4m = 0.6m
( here as the signal from the transmitter first reached the water surface then reflect back from it to receiver hence it travels twice the distance of the actual distance between object and sensor that's why actual distance = (speed*time taken to receive signal)/2
Ans 4) Option D: -2.
as Vo= 1-3= -2 (noninverting input-inverting input).
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