Radio,Television And Electronic Paper 2, WASSCE (SC), 2022

Question 2

 

 

  1. Draw the circuit diagram of the device in Fig. 1.
  2. If each of the cells has an e.m.f. of 1.5 V and the bulb is rated 5 W, calculate the
  3. Current flowing in the circuit;
  4. Resistance of the circuit.
  5. A using the flashlight for a few hours, there was a noticeable difference in the brightness of the bulb. Suggest:
  6. The difference that could have been observed;
  7. One reason for your answer in 2(c)(i).
  8. To solve the problem of buying cells several times, the instructor directed the student to convert the flashlight to a rechargeable type. Complete Table 2 by giving two of the additional equipment needed and the purpose which each will serve in the new circuit.


Table 2


S/N

Additional component

Purpose in the new circuit

(i)

 

 

(ii)

 

 

 

Observation

The expected responses were:

(a) Circuit diagram of the flashlight in Fig.1
 

 


                                                                                                                       
(b)    V = 1.5 + 1.5 = 3.0                    
P = 5 W

  • Current flowing in the circuit

I =  =  = 1.67 A                 

  • Resistance in the circuit

R=  =  = 1.80 Ω     
Or                                                              

(c) (i) the brightness decreases | reduces | the bulb goes dim                                     
(ii) Reasons for the Observations in 2(c)(i)

  • the e.m.f. of the battery reduces
  • the battery drains
  • current in the circuit reduces                                                             

(d)       Components needed to convert flashlight to rechargeable type


S/N

Additional component

Purpose in the new circuit

(i)

Rechargeable cells

To ensure that charge can be stored

(ii)

Diode

To convert a.c. current from the mains to d.c. which will charge the cells

(iii)

Capacitor

To store charge temporarily,
It removes/filters ac voltage
It is used to reduce ac voltage magnitude before rectification

(iv)

LED

To  indicate charging process

(v)

Resistor

To limit current

(vi)

AC plug/socket

To connect external grid or external supply source for recharging

(vii)

Transformer

To reduce ac voltage in purpose built charger