Which one among the following is not an electromagnetic wave?

Introduction / Context:
Electromagnetic waves form a broad spectrum that includes radio waves, microwaves, infrared, visible light, ultraviolet, X rays and gamma rays. These waves consist of oscillating electric and magnetic fields and can travel through vacuum. In contrast, some types of radiation are streams of particles with mass and charge. This question asks you to distinguish between true electromagnetic waves and particle rays such as cathode rays.

Given Data / Assumptions:

• X rays and gamma rays are high energy parts of the electromagnetic spectrum.
• Infrared rays are lower frequency electromagnetic waves associated with heat radiation.
• Cathode rays are streams of electrons emitted from the cathode in a discharge tube.
• We are choosing which option is not an electromagnetic wave.

Concept / Approach:
Electromagnetic waves are massless and electrically neutral disturbances that propagate at the speed of light in vacuum. They do not consist of moving material particles. Cathode rays, on the other hand, are actual electrons moving at high speed in a vacuum tube. Because electrons have mass and negative charge, cathode rays are considered streams of charged particles, not electromagnetic waves. X rays, gamma rays and infrared rays all belong to the electromagnetic spectrum, differing only in frequency and wavelength. Therefore, cathode ray is the correct choice as not being an electromagnetic wave.

Step-by-Step Solution:
Step 1: Recall that X rays are high energy electromagnetic waves used in medical imaging.Step 2: Recall that gamma rays are even higher energy electromagnetic waves emitted in nuclear transitions.Step 3: Recall that infrared rays are lower energy electromagnetic waves associated with heat and thermal radiation.Step 4: Understand that cathode rays are electrons emitted from a heated or negatively charged cathode in a discharge tube.Step 5: Note that electrons have rest mass and electric charge, so a beam of electrons is not an electromagnetic wave.Step 6: Conclude that cathode ray is the only option that is not an electromagnetic wave.

Verification / Alternative check:
Historical experiments with cathode ray tubes showed that cathode rays are deflected by electric and magnetic fields in a way consistent with negatively charged particles. J J Thomson measured the charge to mass ratio of cathode ray particles and identified them as electrons. Electromagnetic waves, in contrast, are not deflected in the same way because they are not charged particles. X rays, gamma rays and infrared rays are all produced and detected by methods involving accelerating charges and transitions in atoms, consistent with electromagnetic theory.

Why Other Options Are Wrong:
X rays are electromagnetic waves with very short wavelength and high energy, widely used in medicine and material testing. Gamma rays are even more energetic electromagnetic waves associated with nuclear processes. Infrared rays are part of the electromagnetic spectrum with longer wavelength than visible light and are felt as heat. All three are genuine electromagnetic waves and therefore cannot be the correct answer for a question asking which is not an electromagnetic wave.

Common Pitfalls:
Students may be misled by the word ray, assuming that anything called a ray must be electromagnetic. However, cathode rays are an important exception because they are beams of electrons. It is important to distinguish naming conventions from physical nature. Remember that electromagnetic waves are massless and neutral, while cathode rays are made of particles with mass and charge.

Final Answer:
Cathode ray is not an electromagnetic wave; it is a stream of electrons.