Question 1
- List:
- four component parts of a cathode ray tube;
- three a.c. quantities that can be measured by the cathode ray oscilloscope.
- State the:
- type of multivibrator used in the cathode ray oscilloscope;
- function of multivibrator in 1(b)(i).
The expected responses were:
(a) (i) Component parts of a cathode ray tube
- Cathode
- Grid
- Accelerating anode
- Focusing anode
- X – plate
- Y – plate
- Screen
- Pre-accelerator anode
(ii) AC quantities that can be measured by cathode ray oscilloscope
- Voltage
- Current
- Frequency
- Period
- Phase shift
(b) (i) Triggered/Astable multivibrator
(ii) Provides/serves as a time base generator
This question tested the familiarity of the candidates with the cathode ray tube and the oscilloscope. It was reported that in question (a), only a few candidates listed more than two of the component parts of a cathode ray tube. Likewise, many candidates could not provide the quantities that can be measured by a CRO.
The oscilloscope has a time base (a saw-tooth signal generator), whose functionality is controlled by a trigger circuit. It is correct therefore, to state that the oscillator is a triggered- astable multivibrator, which functions to provide the time-base signal. Majority of the candidates did not respond well to question (b).