CIE iGCSE Co-Ordinated Science P2.3.1 Conduction Exam Style Questions Paper 3
Question
A room in a house has an electric heater.
(a) Fig. 12.1 shows part of the circuit containing the heater.
Complete the circuit diagram in Fig. 12.1 by adding the correct electrical symbol for a fuse.
(b) When the circuit is switched on, the current in the heater is 3A and the supply voltage is 240V.
(i) Calculate the resistance of the heater.
State the unit of your answer.
resistance = ……………………………….. unit ………..
(ii) The fuse in the circuit needs to be replaced.
Explain why a 5A fuse is used and not a 3A fuse.
(c) Fig. 12.2 shows the heater as part of an underfloor heating system.
(i) When the heater is switched on, thermal energy passes through the solid floor to heat the air in the room.
The temperature of the air in the room increases slowly.
State the method of thermal energy transfer through the solid floor.
(ii) State the method of thermal energy transfer that heats all the air in the room.
(d) Some water spills onto the floor and evaporates.
Describe evaporation in terms of the motion of water molecules.
(e) There are solar cells on the roof of the house.
State one advantage and one disadvantage of generating electricity using solar cells. Do not include the cost.
advantage ………………………………………………………………………
disadvantage ………………………………………………………………….
▶️Answer/Explanation
Ans : 12(a) fuse inserted in gap using the correct symbol ;
12(b)(i) evidence of resistance = voltage / current (in any form) or 240 / 3 ;
= 80 ;
Ω / ohms ;
12(b)(ii) fuse needs to be slightly greater than maximum current (or it would blow in normal use) ;
12(c)(i) conduction ;
12(c)(ii) convection ;
12(d) faster moving / most energetic molecules (leave) ;
(leave) from the surface of the liquid ;
12(e) renewable energy / does not produce CO2 etc ;
need sunlight / only works during the day etc ;
Question
(a) An electric heater is used to heat a classroom in a school.
The arrows on Fig. 12.1 show the circulation of air around the classroom.
P and Q are two positions within the air circulation.
Complete the sentences using words from the list.
conduction convection cooled radiation warmed
Position P shows ………………………………. air.
Position Q shows ………………………………. air.
This method of thermal energy transfer is called ………………………………. .
(b) In the classroom, a student draws diagrams to represent the three states of matter.
Fig. 12.2 shows the diagrams drawn. Box X shows the arrangement of particles in a solid.
Box Y shows the arrangement of particles in a liquid.
(i) In box Z, draw the arrangement of particles in a gas.
(ii) Complete the sentences below using only the words solid, liquid and gas.
Solidification occurs when a …………………………….. turns into a …………………………….. .
Condensation occurs when a …………………………….. turns into a …………………………….. .
(iii) State the melting point and the boiling point of water at standard atmospheric pressure.
melting point = ……………….. °C
boiling point = ………………… °C
(c) In another lesson, the student builds an electric circuit.
Fig. 12.3 shows the circuit diagram.
(i) State the name of the components represented by the symbols in Table 12.1.
(ii) When there is a potential difference of 6V across the lamp, a current of 0.3A passes through the lamp.
Calculate the resistance of the lamp.
resistance = …………………………………………….. Ω
▶️Answer/Explanation
Ans: 12(a) cooled ;
warmed ;
convection ;
all correct ;
12(b)(i)
random arrangement and widely spaced ;
12(b)(ii) liquid and
solid ;
gas and
liquid ;
12(b)(iii) 0 °C and 100 °C ;
12(c)(i) ammeter ;
voltmeter ;
12(c)(ii) R = V ÷ I (symbols or words) or 6 ÷ 0.3 ;
R = 20 (Ω) ;
Question
Fig. 9.1 shows a refrigerator.
(a) The freezing compartment at the top of the refrigerator cools all the air in the refrigerator.
State the main method of thermal energy transfer used in this cooling process.
▶️Answer/Explanation
Answer:
Convection
Explanation:
Convection is the main method of thermal energy transfer in the refrigerator. Cold air from the freezing compartment sinks, and warmer air rises, creating a convection current that cools the entire refrigerator.
(b) The volume of air in the refrigerator is 210 000 cm3.
The density of air is 0.00126 g/cm3.
Calculate the mass of air in the refrigerator. Show your working.
Mass = …… g
▶️Answer/Explanation
Answer:
265 g
Explanation:
Mass = Density × Volume
Mass = 0.00126 g/cm3 × 210,000 cm3
Mass = 265 g
(c) A liquid-in-glass thermometer is placed inside the freezing compartment to measure a temperature of –20 °C.
- Name a suitable liquid to use in the thermometer.
- State the physical property of the liquid that varies with temperature in a liquid-in-glass thermometer.
▶️Answer/Explanation
Answer:
1. Mercury or alcohol
2. Volume
Explanation:
– Mercury or alcohol is commonly used in liquid-in-glass thermometers because they expand and contract predictably with temperature changes.
– The volume of the liquid changes with temperature, causing it to rise or fall in the thermometer’s narrow tube.
(d) The refrigerator emits a quiet sound with a low pitch.
- Describe the amplitude and frequency of this sound.
Amplitude
Frequency - State the unit of frequency.
▶️Answer/Explanation
Answer:
1. Small amplitude, low frequency
2. Hertz (Hz)
Explanation:
– A quiet sound has a small amplitude, and a low-pitched sound has a low frequency.
– The unit of frequency is hertz (Hz), which measures the number of vibrations per second.
(e) The refrigerator contains two lamps connected in series.
Lamp A has a resistance of 4000 Ω and lamp B has a resistance of 5000 Ω.
- Calculate the combined resistance of the two lamps connected in series.
Resistance = …… Ω - The potential difference across the lamps is 240 V. Use your answer to (e)(i) to calculate the current in the lamps. Show your working.
Current = …… A
▶️Answer/Explanation
Answer:
1. 9000 Ω
2. 0.027 A
Explanation:
1. Combined resistance in series = R1 + R2
Combined resistance = 4000 Ω + 5000 Ω = 9000 Ω
2. Current (I) = Voltage (V) / Resistance (R)
I = 240 V / 9000 Ω = 0.027 A
Question
(a) Fig. 3.1 shows water in a saucepan on an electric cooker. (Sub-topic – P2.3.1)
State the process that transfers thermal energy through the base of the saucepan.
▶️Answer/Explanation
Answer:
Conduction
(b) The temperature of the water is recorded as the saucepan is heated. (Sub-topic – P2.2.2)
Fig. 3.2 shows a graph of the results.
(i) State the temperature rise over the first 2 minutes.
……………….. °C
▶️Answer/Explanation
Answer:
38 °C
(ii) State how the graph shows that the water boils at 100°C.
▶️Answer/Explanation
Answer:
The temperature stops increasing at 100°C, indicating that the water is boiling.
(c) (i) The saucepan is made from steel.
State one difference between the magnetic properties of steel and the magnetic properties of soft iron. (Sub-topic – P4.1)
▶️Answer/Explanation
Answer:
Steel is magnetised slowly and retains its magnetism, while soft iron is magnetised quickly but loses its magnetism easily.
(ii) The mass of steel used to make the saucepan is 900g.
The volume of the steel is 115cm3.
Calculate the density of the steel used to make the saucepan.
State the units of your answer. (Sub-topic – P1.4)
density = ……………………………. units …………..
▶️Answer/Explanation
Answer:
Density = mass + volume
or mass value ÷ volume value
or 900 + 115 = 7.83 g/cm3
(d) When the base of the steel saucepan is heated, the steel expands. (Sub-topic – P2.2.1)
(i) State one example where the thermal expansion of a material is useful.
▶️Answer/Explanation
Answer:
(liquid in glass) thermometers / bimetallic strips ;
(ii) State one example where the thermal expansion of a material is a problem.
▶️Answer/Explanation
Answer:
bridges / roads / overhead electricity cables etc. ;