Figure 14 (a) is a diagram of a cathode ray tube. M and N are parallel vertical plates
(a) When switch S is open, a spot is seen at the centre of the screen as shown in figure 14(b).
(i) State what happens to the sport when S is closed.
(ii) State what would happen to the spot if the potential difference across MN is increased.
(iii) State what would be seen on the screen if the battery is replaced with an alternating
e.m.f of:
(I) A low frequency of about 1Hz,
(II) A high frequency of about 50Hz.
(b) Explain the process by which electrons are produced are produced at F.
(c) State with a reason how the brightness of the spot can be increased.
(d) The accelerating voltage of the tube is 1000V and the electron in the beam is 1.5mA.
Determine the energy conveyed to the screen per second.
Answer:
a) i) - It deflects towards the positive plate i.e towards N.
ii)- Deflection will be greater, it increases.
iii)
I)The spot will move back and forth or to and fro it oscillate.
II)- There will be a horizontal line.
b)
-The heating effect of the current increases the energy of the electrons.
As a result, they break off the surface
c)-By increasing the filament current so that more electrons are released
d)
P=VI
=#1000 times 1.5times10^(-3)#
=1.5 Joules.
ii)- Deflection will be greater, it increases.
iii)
I)The spot will move back and forth or to and fro it oscillate.
II)- There will be a horizontal line.
b)
-The heating effect of the current increases the energy of the electrons.
As a result, they break off the surface
c)-By increasing the filament current so that more electrons are released
d)
P=VI
=#1000 times 1.5times10^(-3)#
=1.5 Joules.
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The control grids in a Cathode Ray Oscilloscope (CRO) is used to control the brightness of the beam on the screen. How is this achieved? 
