Question
Fig. 9.1 shows an electric circuit.
(a) When the circuit is in a cool room, the voltmeter reading is 5.6 V and the ammeter reading is 0.040 A.
Calculate the resistance of the thermistor.
resistance of thermistor = …………………………………………….. Ω
(b) The temperature of the thermistor increases and the buzzer turns on.
State and explain how the increase in temperature affects the current in the thermistor.
(c) Suggest a possible use for the circuit shown in Fig. 9.1.
Answer/Explanation
Answer:
(a) V= IR or (R =) V / I
5.6 ÷ 0.04
140 (Ω)
(b) (current in thermistor) increases
(because) resistance of thermistor decreases
(c) fire / high temperature alarm / warning
Question
Fig. 9.1 and Fig. 9.2 each show an electrical circuit. Each circuit has two lamps connected to an electrical supply.
(a) State the term used to describe each electrical circuit. Write the term under each circuit.
(b) State two disadvantages of the circuit in Fig. 9.2.
1. ……………………………………………………………………………………………………………………………..
2. ……………………………………………………………………………………………………………………………..
(c) Redraw the circuit in Fig. 9.1 with switches that will turn lamps X and Y on and off independently of each other.
(d) Fig. 9.3 shows another circuit.
The lamps can be turned on and off using two different switches S1 and S2.
Complete the table stating when the lamps are on or off. The first one has been done for you.
|
switch positions |
lamps on or off |
|
|
S1 |
S2 |
|
|
K |
Z |
off |
|
K |
W |
|
|
J |
W |
|
|
J |
Z |
|
Answer/Explanation
Answer:
(a) (Fig. 9.1 is a) parallel (circuit)
(Fig. 9.2 is a) series (circuit)
(b) Any two from:
lamps less bright
if one lamp breaks the other does not light
lamps cannot be switched independently
(c) two correct switch symbols
switch on each branch
(d) (K W) on
(J W) off
(J Z) on