waecE-LEARNING
Radio, TV & Electr. Work Paper 2, May/June 2014  
Questions: 1 2 3 4   Main
General Comments
Weakness/Remedies
Strength













































Question 4

Question 4
                        (a)        Define
                                    (i)         thermionic emission;
                                    (ii)        photoelectric emission.

                        (b)        State one application each of the emissions defined in 4 (a).
                        (c)        Complete Table 1.

                                                                      Table `1                       


TRANSDUCER TYPE

CONVERSION

APPLICATION

FROM

TO

Loudspeaker

Electrical energy

Sound energy

Public address system

Microphone

 

 

 

 

 

 

Waveform display

 

Moving picture

 

 

                         The expected answers were:
(a)(i)    Thermionic emission is the process of liberating electrons from the surface of a  metal when the metal is heated.                                                                              
    (ii)  Photoelectric emission is the emission of electrons from a metallic
           surface  when light of certain frequency is incident on it.
                                               
                         (b)(i) Any one application of thermionic emission
                            -       Thermionic converter
                            -       Electron tube or valves

     (ii) Any one application of thermionic emission
                       -            Solar cell
           -            Photoconductive  devices
           -            Photo cells
           -            Security doors
           -            Alarm circuit
           -            Security light
           -            Charging system
                                                                       
            (c)   


TRANSDUCER TYPE

CONVERSION

APPLICATION

FROM

TO

Loudspeaker

Electrical energy

Sound energy

Public address system

Microphone

Sound energy

Electrical energy

Public address system

Cathode Ray Tube (CRT)

Electrical energy

Light

Waveform display

Digital camera

Moving picture

Electrical signal

Video recording or CCTV

  
            The question was on Electronic devices and circuits. It was unpopular with the candidates. It showed that many candidates that attempted it had little depth of knowledge. The performance of candidates was reported to be average.

 

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