what is the difference between ultrasonic sensors and normal sensors?

Answer 1

I have no idea what a "normal" sensor is.

And ultrasonic sensor relies on acoustic energy above human hearing range, that is it uses sound waves that are too high in pitch for humans to hear them. Typically such sensors are used for "non-destructive-inspection" of precision manufactured parts or to measure distances/range finder (essentially sonar), such as early autofocus cameras or map out separation between objects, such as with certain vehicles with back-up assistence systems.

The term is generally misapplied to sensors, as it should be ultrasound, however that term is so closely associated with medical prenatal imaging (which use the same technology greatly enhanced with computer drawn graphics).

The term ultrasonics should be applied only to the devices that use high frequency acoustic energy to change susbstances.

Answer 2

Normal sensors check which are within the normal viewing range.... Ultrasonic sensors check in the frequencies which are beyond the normal viewing range of the humans.