Question

Cathode rays__________.
A. are the atoms moving toward the cathode
B. are electromagnetic waves
C. are negative ions traveling from cathode to anode
D. are electrons emitted by cathode and moving towards anode

Answer 1

Hint: Cathode rays travel in straight lines through the empty tube. These rays carry electric currents through the tube. Cathode rays struck the glass wall of the tube, excite the atoms of the glass and cause them to emit light.

Complete step by step answer:
Cathode rays, or electron beam or e-beam, are streams of electrons being observed in the discharge tubes. If an evacuated and clear glass tube is equipped with two electrodes and a voltage is applied across them, glass behind the positive electrode is observed to glow, due to electrons emitted from the cathode.
Cathode rays, as the name suggests, are the rays emitted by the negative electrode called cathode, in a vacuum tube. To release electrons into the cathode tube, they have to be detached from the atoms of the cathode. Modern vacuum tubes use thermionic emission, in which the cathode is made of a thin filament of wire which is heated by a separate electric current passing through it. The increased random motion of the filament produces heat and knocks electrons out of the surface of the filament, directly into the evacuated space of the tube.

The electrons carry negative charge. As a result, they are repelled by the negative cathode and attracted towards the positive anode. They move in straight lines through the empty tube. The voltage applied between the electrodes of the tube accelerates these low mass particles, electrons, to high velocities. Cathode rays struck the glass wall of the tube, excite the atoms of the glass and cause them to emit light. This glow is called fluorescence.
Cathode rays are the electrons emitted by cathode and moving towards anode.
Hence, the correct option is D.

Note:
The cathode is a negatively-charged electrode or conductor, and the anode is a positively-charged conductor. Electrons carry negative charge, so they flow off the cathode and are attracted towards the positive electrode, anode. A tiny hole in the anode allows some of the electrons to pass through it, creating a beam of electrons, known as cathode rays.