Which waves are used in sonography?
(a). Microwaves
(b). Infrared rays
(c). Radio rays
(d). Ultrasonic rays

- Hint: Here, one should know the difference between all the electromagnetic waves spectrum. There are many rays in the spectrum, but we use only a few rays in routine like X-rays to scan bones in the body, Ultraviolet rays which come from sunlight, etcetera. So, in this question some uses of rays should be known.

Complete step-by-step solution -

Now, let’s start with option (a): Microwaves are used in point to point communication systems to transmit data like voice, signal in analog and digital form. These waves have frequencies ranging from 1 Gigahertz to 300 Gigahertz.

Now, taking option (b): Infrared radiation is also known as IR is a type of energy which is invisible to human eyes but can feel in the form of heat. Its frequencies range from 300 Gigahertz to 400 Terahertz. Anything around the temperature of 5degree Kelvin emits IR radiation. For example: TV remote control which relies on infrared radiation, energy comes out from light emitting diode (LED) and strikes a TV receiver section and thus remote works and we can change channels.

Now, option (c): Radio rays are part of the electromagnetic spectrum which have frequencies more than microwaves. Range is 3hertz to 1 Gigahertz. These waves are used in standard radio and Television broadcast, line to line communications, cellular telephony, etcetera.

Now, option (d): Ultrasonic waves or ultrasound is a technique which uses high frequency sound waves and echo. Its frequencies range from 1 to 5Gigahetrz. It is highly used in the medical field to detect pregnancy. It is also used in submarines as SONAR.

Thus, option (d) is the correct answer.

Note: In this type of theoretical question, one should remember some basic applications regarding all the waves or rays present in the spectrum along with some approx. frequency range to avoid mistakes in exams. Otherwise, there are high chances of getting answers wrong in these simple questions.