a) List two properties of cathode rays. (b) Explain how the intensity and energy of cathode rays may be increased

Answer Details

(a) Two properties of cathode rays

• They travel in straight lines and cast sharp shadows of objects placed in their path.
• They are streams of negatively charged particles (electrons); hence they are deflected by both electric and magnetic fields (towards the positive plate).

(Other valid properties: they possess kinetic energy and momentum, they can produce heat, they cause certain substances to fluoresce, and they can produce X-rays on striking a metal target.)

(b) Increasing the intensity and energy of cathode rays

Intensity: The intensity (number of electrons emitted per second) is increased by raising the temperature of the cathode/filament, that is by increasing the heating (filament) current. A hotter cathode emits more electrons per second by thermionic emission, giving a more intense beam.

Energy: The energy (speed) of the cathode rays is increased by raising the accelerating potential difference (the anode voltage) between the cathode and anode. Each electron gains energy \(eV\), so a larger \(V\) gives faster, more energetic electrons.