Download F.2 IS Workbook Chapter 8 Answers

F.2 IS Workbook Chapter 8 Answers
8.1 Making Electricity Flow and 8.2 Electrical conductors and insulators
1. F
2. T
3. F
4. T
5. T
Questions
1. (a) The bulb will not light up because the circuit is not closed (or complete).
(b) The bulb will not light up because the bulb is not in the closed circuit (or there is no current
flowing through the bulb)
(c) The bulb will light up because the bulb is in a closed circuit with dry cells.
(d) The bulb will light up because the bulb is in a closed circuit with dry cells.
(e) The bulb will not light up because there is no electricity supply (or dry cells).
3. Conductors: iron nail, mercury, silver
Insulators: glass, wood, plastic, paper, stone
4. No. If there is a path for electricity to flow to the tram but no path for it to leave the tram, it is
not a complete circuit and no electricity will flow through the tram. In fact, the other path is the rail.
8.3
1.
4.
6.
Electric current + 8.4 voltage
ampere, volt
2. free electrons
dry cell, wire, free electrons/current
battery
7. greater
3.
5.
voltage
ammeter, voltmeter
Questions
1. (b) Connect one more dry cell to the circuit. The two dry cells should be placed in the same
direction.
(d) The reading of the ammeter in (c) is higher. This is because the voltage supplied by the two
cells is higher, so the current flowing through that circuit is larger.
2.
(b)
(d)
(e)
The reading of voltmeter is 1.5 V.
The reading of the voltmeter is 3 V.
The bulb in (c) is brighter.
8.5 Resistance
1.C
2.D
3.B
Fill in the blanks
1. ohm
4. higher
4.A
2.
5.
resistance
rheostat
3.
higher
Questions
1. Measure the resistance of the bulb with the multimeter. If the resistance is very large, then
filament is broken.
2. (b) Turn the rotating contact in anti-clockwise direction.
(c) Terminals B and C.
(d) Turn the rotating contact in clockwise direction.
(e) Dimmers / Volume control
8.6 Circuit symbols
Multiple Choice
1.B
2.C
3.C
Questions
1. (a) dry cell
(d) ammeter
(g) rheostat
(b)
(e)
(h)
battery
voltmeter
switch
(c)
(f)
bulb
resistor
8.7 Series and parallel circuits
1.T
2.T
3.F
4.F
Multiple Choice
1.A
2.A
3.B
Questions
1. (a) series
series
(e)
5.F
6.T
(f)
(c) parallel
parallel
4.B
(b) series
parallel
(d)
(g)
series
2.
(b) dry cells, switch, rheostat and ammeter
(c) voltmeter and resistor
(d) Move the sliding contact towards Q
(e) Connect one more dry cell to the circuit. The two dry cells should be connected in the same
direction. (OR replace the existing resistor with the one with lower resistance)
8.8 Fuses
Concept checking
1.T
2.T
3.F
4.T
Multiple Choice
1.B
2.C
3.D
4.B
5.T
6.F
Questions
1. (a) fuse rating
(b) glass casing
(c) metal contact cap
(d) fuse wire
2. (a) A fuse is used to prevent an excessive electric current from flowing through the circuit.
(b) The fuse and the electrical appliance should be connected in series.
(c)
(d) The melting point of the thin wire should be low.
(e) It is the fuse rating. It means that 3A is the maximum current that can flow through the fuse
without melting.
8.9 Household electricity
Multiple Choice
1.C
2.B
3.B
Fill in the blanks
1. 220 V
4. ring circuit
4.C
2.
5.
earth
3.
overloading
ground, earthing
Questions
1. (a) live wire
(b) neutral wire
(c) earth wire
(d) fuse
2. (a) neutral socket (b) earth socket
(c) live socket
3. The ammeter reading will increase and the bulb will glow brighter. This is because a short circuit
is formed and its resistance is very low.
8.10 Power of an electrical appliance
1.T
2.F
3.F
4.F
5.T
Questions
1. (a) The numbers 40 W and 60W indicate the power of the bulb. The marking 220 V indicates
the voltage at which the bulbs should work.
(b)
Current through bulb A = 40 / 220 = 0.18 A
Current through bulb B = 60 / 220 = 0.27 A
2.
Power required = IV = 5 x 220 = 1100 W
3.
(a)
(i)
Electric current = P / V = 500 / 200 = 2.5 A
(ii) Electric current = 1000 / 200 = 5A
(b)
Resistor A has a higher resistance as it allows a smaller current to flow through it.
8.11 Cost of electricity
1.F
2.F
3.T
4.T
5.T
Questions (P.56)
1.
(a) Cost per kWh = 705.76 / 802 = $ 0.88
(b) Amount being saved = 3 x 1.2 x 120 x 0.88 = $ 380.16
(c) In normal use, the air conditioners do not always operate at their maximum power (i.e.
1200 W). When the room temperature is low enough, the cooling operation of the air conditioners will
stop and so the energy consumed per second will be much lower. Therefore, the amount of electricity
consumed by the air conditioners is smaller than the expected value.
8.12 Working principle of common electrical appliances
1,F
2.T
3.T
4.F
5.T
Questions (P.59)
Heating effect
Magnetic effect
Part B
A,E,F,I
A, B, C, D, G, H
Integrated Exercise
1
F
2
F
3
F
4
T
5
T
6
T
7
F
8
F
9
T
10
T
11
F
12
F
Multiple Choice
1
B
2
D
3
D
4
D
5
D
6
D
7
D
Questions
1.
(a)
(c)
The rheostat is connected wrongly.
The reading of the ammeter decreases.
2.
(b)
Green and yellow : earth wire
Brown : live wire
Blue : neutral wire
8
B
9
C
10
B
11
B
12
A
13
D
14
C
15
A
(c) No. The earth wire is a safety device which protects people from getting an electric shock.
If there is a fault in the cooker, resulting in a leakage of current to the metal case, the leaked current
will flow through the earth wire to the ground. If the earth wire is not connected, the person who
touches the metal case of the cooker will receive an electric shock.
(d) When the cooker is switched on, the electric current flowing through the cooker is greater
than 3A. The 3A fuse will melt and an open circuit is formed. Therefore, the cooker does not work.
4.
(a) Electric current = 2 / 5 = 0.4 A
(b) If one of the bulbs burns out, all the other bulbs will not light up.
(c) A fuse should be connected in series with the set of Christmas tree lights.
(d) If the filament of a bulb burns out, the electric current can flow through that bulb via the
shunt wire, even the bulb does not light up. The circuit is still closed and therefore the rest of the
bulbs can light up.
5.
(a)
(c)
(d)
They are connected in parallel.
Total current = 100 / 220 + 1500 / 220 = 7.27 A
(i) Total current = 7.27 + 1300 / 220 = 13.2A
(ii) The fuse will melt and the circuit will be broken. All the three electrical appliances
will stop working.
(e) No, when he connects five types of electrical appliances with a low power to the extension
unit, the electrical appliances can work properly at the same time if the total current drawn from the
mains socket is smaller than 13 A. He can then use all the sockets in the extension unit at the same
time.
6.
(a)
Lamp
Washing machine
Air conditioner
Refrigerator
Television
Rice cooker
Water heater
(b)
(c)
0.45 A
1.82
11.36
0.91
0.68
6.82
8.18
1
3
13
1
1
10
10
Total units used = 1637.8 kWh
Total cost = $1521.8
(i) The air conditioner takes up the largest part of the cost of electricity.
(ii) Use electric fans instead of air conditioners to reduce the cost of electricity.