(a) State two properties of cathode rays. (b) Explain how the intensity and energy of cathode rays may be increased.
Question 1 Report
(a) State 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 from the cathode and cast sharp shadows of objects placed in their path.
- They are streams of negatively charged particles (electrons), so they are deflected by both electric and magnetic fields (towards the positive plate).
Other acceptable properties: they carry energy and momentum, they produce heat and fluorescence on striking a screen, and they can produce X-rays on hitting a metal target.
(b) Increasing the intensity and energy of cathode rays
Intensity (number of electrons per second) is increased by raising the filament (heater) current. A hotter cathode emits more electrons by thermionic emission, so the beam current and hence the brightness increase.
Energy (speed of each electron) is increased by raising the accelerating potential difference between the cathode and the anode. Each electron gains kinetic energy \(eV\) as it is accelerated, so a larger anode voltage gives faster, more energetic electrons.
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