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
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