Radio,Television And Electronic Paper 2, WASSCE (SC), 2019

Question 3.

 

  1. State three differences between:
    1. primary cells and secondary cells;
    2. direct current and alternating current.
  2. Fig. 2 is the diagram of a metering coil ammeter reading in milliameter range.
    1. Name the parts labelled P and Q;
    2. State the reading displayed by the instrument.
  3. if the reading of the instrument in Fig. 2 was recorded when it was connected to circuit of 1 resistance, calculate the:

    1. Voltage drop in the circuit;
    2. Power dissipated by the circuit.   

 

Observation

The expected answers were:

The expected responses were:
(a)        (i)         Differences between primary cells and secondary cells


Primary cells

Secondary cells

They are not rechargeable

They are rechargeable

They are usually light in weight

They are usually heavy

Electrolytes are usually in solid/paste form

Electrolytes are usually in liquid form

They are usually single celled

They are usually multi-celled

They have shorter shelf life

They have longer shelf life

They are cheaper

They are more expensive

                                   
(ii)        Differences between direct current and alternating current


Direct Current

Alternating current

Its output is a straight line

Has a sinusoidal/non-linear waveform

Has no frequencyor zero frequency

Has frequency/ has non-zero frequency

Total electrical energy is effective energy.

Total electrical energy is not effective energy.

Non- reversible polarity

Reversible polarity

Its source is battery/solar cells

Its source is the mains/generator

Current flows in one direction

Current direction is reversible.

                                               
(b)        (i)         P – pointer                                          
Q – permanent magnet
(ii)        Reading = 2.7 – 2.9 mA.                                                                                                
(c)        (i)                                              
    (to )    
                                                                                 
(ii)                  OR      P = V2/R                      OR                                                                                         OR                 
      7.29mW                    

It was reported that majority of the candidates that attempted Question 3 responded very well. Only a few candidates could not read the ammeter scale appropriately.