K.C.S.E Physics Q & A - MODEL 2011PP2QN18

K.C.S.E Physics Q & A - MODEL 2011PP2QN18

​(a) State two differences between cathode rays and electromagnetic radiations. 
(b) Figure 10, shows the main features of a cathode ray oscilloscope (CRO)

​(i) Name the parts labelled M and N. 
M
N
(ii) Explain how electrons are produced in the tube. 
(iii) When using the CRO to display waveforms of voltages, state where the following should be connected:
(I) the voltage to be displayed on the screen; 
(II) the time base voltage. 
(iv) state why the tube is highly evacuated. 
(c) Figure 11, shows the waveform of a voltage displayed on the screen of a CRO.
The Y-gain calibration was 5V per cm.

​(i) Determine the peak-to-peak voltage of the Y-input. 
(ii) Sketch on the same figure the appearance of the waveform after the voltage of the input signal is halved and it’s frequency is doubled. 

answers

(a) -Cathode rays have charge but e.m  radiations don’t have charge;
-Cathode rays are particles and have a mass but e.m radiations are waves;
-Cathode rays travel at a speed depending on the accelerating voltage but e.m radiations
travel at the speed of light in vacuum;
- Different in the mode of production.
(b) (i) M - grid;
N - accelerating anode/anode/vacuum;
(ii) Cathode is heated by filament;
electrons are released from cathode;
by thermionic emission
(iii) (I) across Y-Y plates.
(Il) across X-X plates. (2 m
(iv) to reduce collisions, (hence ionization) with air molecules in the tube.
(c) (i) peak-to-peak voltage = 5 x 2 =10v