Question 1
(a) Fig. 1.1 is a diagram of a section through the heart and associated blood vessels.
(i) Name the structure labelled X in Fig. 1.1. (Sub-topic: B9.2)
▶️Answer/Explanation
Septum
(ii) Name the structure shown in Fig. 1.1 that ensures one-way flow of blood. (Sub-topic: B9.2)
▶️Answer/Explanation
Valve
(iii) Draw an arrow on Fig. 1.1 to show where blood enters the heart from the lungs. (Sub-topic: B9.2)
▶️Answer/Explanation
Arrow pointing into the heart from the pulmonary vein (furthest right blood vessel).
(b) Table 1.1 shows some of the functions of the components of blood. Complete Table 1.1 by adding the name of the component of blood which has each function. (Sub-topic: B9.4)
| Component of Blood | Function |
|---|---|
| …. | Antibody production and phagocytosis |
| …. | Promotes blood clotting |
| …. | Transport of dissolved nutrients |
| …. | Transport of oxygen |
▶️Answer/Explanation
See table below.
(c) Substances are transported around the body by blood in blood vessels. Substances are also transported around plants in vessels.
Name the two vessels that transport substances in plants. (Sub-topic: B8.1)
▶️Answer/Explanation
Xylem and phloem
(d) Water is one of the substances transported through plants and is lost by the process of transpiration.
Complete the definition of the term transpiration using words or phrases from the list. (Sub-topic: B8.3)
Each word or phrase may be used once, more than once or not at all.
absorption diffusion epidermis evaporation
palisade cells photosynthesis roots stomata
Transpiration is defined as the loss of water vapour from plant leaves by ………………………….. of water at the surfaces of the mesophyll cells followed by ……………………………….. of water vapour through the ……………………………….. .
▶️Answer/Explanation
Transpiration is defined as the loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata.
Question 2
(a) Fig. 2.1 shows the symbols of six elements and six statements about these elements. On Fig. 2.1, draw one straight line from each symbol to the correct statement.
One line has already been drawn for you. (Sub-topic: C2.2)
▶️Answer/Explanation
Answer:
– Al → the metal obtained from bauxite
– Ca → the metal combined in limestone
– F → a halogen
– C → the element in diamond
– K → a very reactive metal
– S → the element used to make sulfuric acid
Explanation:
– Aluminium (Al) is obtained from bauxite.
– Calcium (Ca) is found in limestone as calcium carbonate.
– Fluorine (F) is a halogen.
– Carbon (C) is the element in diamond.
– Potassium (K) is a very reactive metal.
– Sulfur (S) is used in the production of sulfuric acid.
(b) The chemical symbols of an atom of beryllium and an atom of boron are shown in Fig. 2.2.
Complete Table 2.1 to show the numbers of neutrons and electrons in these atoms. (Sub-topic: C2.2)
| Atom | Neutrons | Electrons |
|---|---|---|
| Be | ||
| B |
▶️Answer/Explanation
Answer:
– Be: Neutrons = 5, Electrons = 4
– B: Neutrons = 6, Electrons = 5
Explanation:
Beryllium (Be) has an atomic number of 4, so it has 4 protons and 4 electrons. The nucleon number is 9, so the number of neutrons is 9 – 4 = 5.
Boron (B) has an atomic number of 5, so it has 5 protons and 5 electrons. The nucleon number is 11, so the number of neutrons is 11 – 5 = 6.
(c) Sodium and chlorine combine to form sodium chloride. Fig. 2.3 shows the electronic structure of an atom of sodium and of an atom of chlorine.
Complete Fig. 2.4 to show the electronic structures of the ions that form from these atoms. (Sub-topic: C2.4)
▶️Answer/Explanation
Answer:
Sodium ion (Na⁺): Loses 1 electron, so it has 10 electrons.
Chloride ion (Cl⁻): Gains 1 electron, so it has 18 electrons.
Explanation:
Sodium (Na) loses one electron to form a sodium ion (Na⁺), leaving it with 10 electrons.
Chlorine (Cl) gains one electron to form a chloride ion (Cl⁻), giving it 18 electrons.
(d) Fig. 2.5 shows apparatus a student uses to produce a neutral solution of sodium chloride.
Apparatus F contains a dilute acid which is added slowly to an alkaline solution contained in the beaker.
(i) Name apparatus F. (Sub-topic: C12.1)
▶️Answer/Explanation
Answer:
Burette
Explanation:
Apparatus F is a burette, which is used to add a solution drop by drop in a controlled manner.
(ii) State the alkaline solution and the dilute acid that react to produce sodium chloride. (Sub-topic: C7.1)
▶️Answer/Explanation
Answer:
Alkaline solution: Sodium hydroxide (NaOH)
Dilute acid: Hydrochloric acid (HCl)
Explanation:
Sodium hydroxide (NaOH) is an alkaline solution, and hydrochloric acid (HCl) is a dilute acid. They react to form sodium chloride (NaCl) and water (H₂O).
(iii) Suggest a value of the pH of the solution in the beaker before any acid is added. (Sub-topic: C7.1)
▶️Answer/Explanation
Answer:
pH > 7 (e.g., pH = 12)
Explanation:
Before any acid is added, the solution is alkaline, so the pH will be greater than 7. A typical value for a strong alkali like sodium hydroxide could be around 12.
Question 3 (Sub-topic: P1.2)
(a) A girl is on a bridge over a river.
(i) Complete the sentences by choosing the correct words or phrases from the list.
Each word or phrase may be used once, more than once or not at all.
chemical constant decreasing friction gravitational potential
increasing joules kinetic newtons weight
The girl picks up a stone and drops it over the side of the bridge.
The stone loses ………………. energy and gains ………………. energy.
The stone falls with ………………. acceleration due to gravity.
The vertical force acting upwards on the stone as it falls is called ………………. and is due to air resistance.
▶️Answer/Explanation
The stone loses gravitational potential energy and gains kinetic energy.
The stone falls with constant acceleration due to gravity.
The vertical force acting upwards on the stone as it falls is called friction and is due to air resistance.
(ii) The river is 30 m below the bridge. After 1.7 s the stone hits the surface of the water. Calculate the average speed of the falling stone.
▶️Answer/Explanation
To calculate the average speed, use the formula:
\[ \text{speed} = \frac{\text{distance}}{\text{time}} \]
Given: distance = 30 m, time = 1.7 s
\[ \text{speed} = \frac{30}{1.7} \approx 17.65 \, \text{m/s} \]
So, the average speed is approximately 17.65 m/s.
(iii) State the source of the gravitational field that is accelerating the stone vertically downwards.
▶️Answer/Explanation
The source of the gravitational field is Earth.
(b) The stone enters the water.
(i) The stone enters the water. Describe how the force of water acting on the stone affects the downwards motion of the stone.
▶️Answer/Explanation
The force of water acting on the stone slows it down or causes it to decelerate.
(ii) The stone enters the water with 450 J of kinetic energy. 200 J is transferred to kinetic energy of the water. 100 J is transferred to thermal energy of the water. 2 J is transferred to sound energy. Determine the remaining kinetic energy of the stone.
▶️Answer/Explanation
To find the remaining kinetic energy, subtract the energy transferred to other forms from the initial kinetic energy:
\[ \text{Remaining kinetic energy} = 450 \, \text{J} – (200 \, \text{J} + 100 \, \text{J} + 2 \, \text{J}) \]
\[ \text{Remaining kinetic energy} = 450 \, \text{J} – 302 \, \text{J} = 148 \, \text{J} \]
So, the remaining kinetic energy is 148 J.
(c) A hydroelectric power station is being built in the river valley.
(i) Describe how electrical energy is obtained from the water behind a hydroelectric dam.
▶️Answer/Explanation
Electrical energy is obtained from the water behind a hydroelectric dam by:
- Water stored behind the dam flows through turbines.
- The flowing water provides kinetic energy to the turbines, causing them to turn.
- The turbines are connected to generators, which convert the kinetic energy into electrical energy.
(ii) The power cables from the power station are supported by pylons. Fig. 3.1 shows the arrangement of the cables between the pylons.
Describe the effect of cold weather on the length of the cables between the pylons.
▶️Answer/Explanation
In cold weather, the cables contract or get shorter due to the decrease in temperature.
(iii) The pylons are spaced equally so that the weight of the cables on each side of the pylon balance. This means the pylons are in equilibrium. State the resultant turning effect on the pylons.
▶️Answer/Explanation
The resultant turning effect on the pylons is zero or none because the forces are balanced.
Question 4
(a) A student investigates the conditions needed for germination of cress seeds. She puts the same number of cress seeds into four test-tubes, A, B, C and D.
The test-tubes are left in different conditions for five days. Table 4.1 shows the conditions of each test-tube and the results after five days.
(i) Explain why the cress seeds in test-tubes A and B did not germinate. (Sub-topic: B15.3)
▶️Answer/Explanation
A – The temperature was too low (4°C), which is not suitable for germination.
B – The seeds were not given water, which is essential for germination.
(ii) State one conclusion from the results shown by test-tubes C and D. (Sub-topic: B15.3)
▶️Answer/Explanation
Light is not necessary for the germination of cress seeds.
(b) Germinating seeds need oxygen for respiration. State the word equation for respiration. (Sub-topic: B12.1)
▶️Answer/Explanation
glucose + oxygen → carbon dioxide + water
(c) Energy released from respiration has many different uses. Put ticks (✓) in the boxes to show all the uses of energy needed by germinating seeds. (Sub-topic: B12.1)
▶️Answer/Explanation
✓ protein synthesis, ✓ cell division, ✓ growth
(d) Respiration is one of the characteristics of living things. Name the characteristic of living things that is defined by: (Sub-topic: B1.1)
the ability to detect and respond to changes in the environment
an action by an organism causing a change of position or place.
▶️Answer/Explanation
sensitivity
movement
Question 5
(a) Meteorites fall to Earth from space.
Some meteorites are mixtures of iron, nickel and other metals.
(i) State the term used for a mixture of metals. (Sub-topic: C9.3)
▶️Answer/Explanation
An alloy is a mixture of metals.
(ii) Metals tend to be shiny and some are sonorous (make a ringing sound when struck).
State two other physical properties of metals. (Sub-topic: C9.1)
▶️Answer/Explanation
1. Metals are malleable (can be hammered into thin sheets).
2. Metals are ductile (can be drawn into wires).
(iii) Name the collection of metals in the Periodic Table that contains iron and nickel. (Sub-topic: C8.4)
▶️Answer/Explanation
Transition elements (or transition metals).
(b) A teacher uses the apparatus shown in Fig. 5.1 to heat four different mixtures containing a powdered metal oxide and powdered carbon.
His observations are shown in Table 5.1.
Use ideas about reactivity to explain the observations. (Sub-topic: C9.4)
▶️Answer/Explanation
Calcium and magnesium are more reactive than carbon, so no reaction occurs when their oxides are heated with carbon. Copper and lead are less reactive than carbon, so carbon can reduce their oxides, resulting in an exothermic reaction.
(c) The symbol equation for the reaction between zinc oxide and carbon is shown.
2ZnO + C → 2Zn + CO2
Use the substances involved in this reaction to describe reduction and oxidation. (Sub-topic: C6.3)
▶️Answer/Explanation
Zinc oxide is reduced because it loses oxygen. Carbon is oxidized because it gains oxygen.
Question 6
(a) Fig. 6.1 shows a bar magnet. It is not known which end is the north pole or the south pole. (Sub-topic: P4.1)
(i) A boy has a second bar magnet. He knows which end is the south pole and which end is the north pole. Describe how he can use the second magnet to determine which end is the south pole and which end is the north pole of the magnet in Fig. 6.1.
▶️Answer/Explanation
The boy can use the second magnet to determine the poles of the magnet in Fig. 6.1 by bringing the known north pole of the second magnet close to one end of the unknown magnet. If the end of the unknown magnet is attracted to the north pole of the second magnet, then that end is the south pole of the unknown magnet. Conversely, if the end of the unknown magnet is repelled by the north pole of the second magnet, then that end is the north pole of the unknown magnet. This is because like poles repel each other, and unlike poles attract each other.
(ii) Draw the pattern and direction of magnetic field lines around the bar magnet in Fig. 6.2.
▶️Answer/Explanation
The magnetic field lines around a bar magnet emerge from the north pole and enter the south pole. The lines should be drawn as continuous curves that loop from the north pole to the south pole, with arrows indicating the direction of the magnetic field (from north to south). The field lines should be closer together near the poles, indicating a stronger magnetic field in those regions.
(b) The boy hears music from a radio. The loudness of the music increases. At the same time, the music changes to a lower pitch. State how the amplitude and the frequency of the sound wave change as the loudness increases and the pitch becomes lower. (Sub-topic: P3.4)
▶️Answer/Explanation
As the loudness of the music increases, the amplitude of the sound wave increases. Amplitude is directly related to the loudness of the sound. As the pitch of the music becomes lower, the frequency of the sound wave decreases. Frequency is directly related to the pitch of the sound. Therefore, an increase in loudness corresponds to an increase in amplitude, and a decrease in pitch corresponds to a decrease in frequency.
(c) The boy has healthy hearing so he can clearly hear the sounds from the radio. State the range of audible frequencies that the boy can hear. (Sub-topic: P3.4)
▶️Answer/Explanation
The range of audible frequencies for a person with healthy hearing is typically from 20 Hz to 20,000 Hz (20 kHz). This range can vary slightly depending on the individual’s age and hearing health.
Question 7
(a) A student investigates the conditions needed for photosynthesis. He keeps similar plants in different conditions for two days and then tests the leaves for starch.
Table 7.1 is a table for the results. (Sub-topic: B6.1)
Complete Table 7.1 to predict the expected results.
▶️Answer/Explanation
Answer:
Test 1: ✓
Test 2: X
Test 3: X
Test 4: X
Explanation:
Photosynthesis requires both carbon dioxide and light. Test 1 has both, so photosynthesis occurs. Tests 2, 3, and 4 lack either carbon dioxide or light, so photosynthesis does not occur.
(b) Describe the test for starch and the positive result. (Sub-topic: B6.1)
▶️Answer/Explanation
Answer:
Test: Add iodine solution to the leaf.
Positive result: The leaf turns blue-black.
Explanation:
Iodine solution is used to test for the presence of starch. If starch is present, the iodine solution will turn blue-black, indicating a positive result for photosynthesis.
(c) Oxygen produced during photosynthesis moves out of the plant cells. Explain in detail how oxygen moves out of plant cells. Use the word concentration in your answer. (Sub-topic: B6.1)
▶️Answer/Explanation
Answer:
Oxygen moves out of plant cells by diffusion. The concentration of oxygen is higher inside the cell than outside, so oxygen diffuses down its concentration gradient through the cell membrane and out of the cell.
Explanation:
During photosynthesis, oxygen is produced as a byproduct. This increases the concentration of oxygen inside the cell. Since the concentration outside the cell is lower, oxygen diffuses out of the cell through the cell membrane, moving from an area of high concentration to an area of low concentration.
(d) Fig. 7.1 is a diagram of a plant cell.
(i) Identify the letter from Fig. 7.1 that shows where photosynthesis occurs. (Sub-topic: B2.1)
▶️Answer/Explanation
Answer:
D
Explanation:
Photosynthesis occurs in the chloroplasts, which are labeled as D in the diagram.
(ii) Name the part you have identified in (d)(i). (Sub-topic: B2.1)
▶️Answer/Explanation
Answer:
Chloroplast
Explanation:
The part identified in (d)(i) is the chloroplast, which is the organelle where photosynthesis takes place.
(iii) Name two parts of plant cells that are also present in animal cells. (Sub-topic: B2.1)
▶️Answer/Explanation
Answer:
1. Cell membrane
2. Nucleus
Explanation:
Both plant and animal cells have a cell membrane and a nucleus. These structures are essential for the basic functions of the cell, such as controlling what enters and exits the cell and storing genetic material.
Question 8 (Sub-topic: C10.2)
Fig. 8.1 is a chart showing the composition of clean air.
(a) (i) Suggest the percentage of the section labelled other gases.
Use your knowledge of the amounts of nitrogen and oxygen in air.
▶️Answer/Explanation
1%
Explanation: Clean air is composed of approximately 78% nitrogen and 21% oxygen. The remaining 1% consists of other gases such as argon, carbon dioxide, and trace amounts of other gases.
(ii) The other gases in Fig. 8.1 include very unreactive elements.
State one of these unreactive elements.
▶️Answer/Explanation
Argon
Explanation: Argon is a noble gas and is very unreactive due to its full outer electron shell.
(iii) State, in terms of electronic structure of its atoms, why the element in (a)(ii) is unreactive.
▶️Answer/Explanation
It has a full outer shell of electrons.
Explanation: Noble gases like argon have a complete outer electron shell, making them stable and unreactive.
(iv) State two harmful gaseous oxides that are present in polluted air.
▶️Answer/Explanation
1. Sulfur dioxide
2. Nitrogen oxides
Explanation: Sulfur dioxide (SO2) and nitrogen oxides (NOx) are harmful gaseous oxides commonly found in polluted air, contributing to acid rain and respiratory problems.
(b) Fig. 8.2 shows apparatus used in the electrolysis of dilute sulfuric acid.
(i) State the term used to describe the dilute sulfuric acid in this electrolysis experiment.
▶️Answer/Explanation
Electrolyte
Explanation: The dilute sulfuric acid acts as an electrolyte, allowing the conduction of electricity through the movement of ions.
(ii) Identify the gas produced at the cathode.
▶️Answer/Explanation
Hydrogen
Explanation: During the electrolysis of dilute sulfuric acid, hydrogen gas is produced at the cathode.
(c) Fig. 8.3 shows apparatus a student uses to investigate the rate of reaction between calcium carbonate and dilute hydrochloric acid.
(i) Complete the word equation for this reaction.
▶️Answer/Explanation
hydrochloric acid + calcium carbonate → calcium chloride + carbon dioxide + water
Explanation: The reaction between hydrochloric acid and calcium carbonate produces calcium chloride, carbon dioxide, and water.
(ii) It takes 50 seconds for 80 cm3 of gas to collect in the gas syringe.
Calculate the rate at which the gas is produced in cm3/s.
▶️Answer/Explanation
1.6 cm3/s
Explanation: The rate of gas production is calculated by dividing the volume of gas by the time taken: 80 cm3 / 50 s = 1.6 cm3/s.
(iii) State one change to the reaction conditions that reduces the rate of reaction.
▶️Answer/Explanation
Decrease the temperature
Explanation: Lowering the temperature reduces the kinetic energy of the particles, leading to fewer effective collisions and a slower reaction rate.
Question 9
(a) A technician is checking for sources of radioactive emissions around a building. (Sub-topic: P5.2.1)
(i) A radiation detector is placed in front of a source of ionising radiation. A piece of paper is placed in front of the source, and the radiation is no longer detected from the source. Identify the type of radiation being emitted by the source.
▶️Answer/Explanation
Alpha radiation (α). Alpha particles are stopped by a piece of paper, which is why the radiation is no longer detected when the paper is placed in front of the source.
(ii) The radioactive source is removed. State why the radiation detector continues to detect a small amount of radiation.
▶️Answer/Explanation
Background radiation. Even when the radioactive source is removed, the detector will still pick up background radiation from natural sources such as cosmic rays, rocks, and building materials.
(b) The graph in Fig. 9.1 shows the decay curve for a radioactive source.
Determine the half-life of the source. Show on the graph how you determined your answer. (Sub-topic: P5.2.4)
▶️Answer/Explanation
The half-life is the time taken for the activity of the radioactive source to decrease to half of its initial value. To determine the half-life from the graph, identify the point where the activity is half of its initial value and read the corresponding time from the x-axis. For example, if the initial activity is 80 counts per second, the half-life is the time it takes for the activity to drop to 40 counts per second. This can be shown by drawing a horizontal line from 40 counts per second to the curve and then dropping a vertical line to the time axis.
(c) The radiation detector is powered by a battery. Fig. 9.2 shows the part of the electrical circuit which lights a lamp when the detector is switched on. (Sub-topic: P4.2.2)
(i) The technician checks the potential difference across the lamp. On Fig. 9.2, add the circuit symbol for a meter to measure the potential difference across the lamp.
▶️Answer/Explanation
To measure the potential difference across the lamp, a voltmeter should be connected in parallel with the lamp. The circuit symbol for a voltmeter is a circle with a “V” inside it. Draw this symbol across the lamp in the circuit diagram.
(ii) The current supplied by the battery is 0.1A. The technician adds another cell to the battery. Describe how the current changes.
▶️Answer/Explanation
Adding another cell to the battery increases the voltage (potential difference) of the battery. According to Ohm’s Law (V = IR), if the resistance of the circuit remains constant, an increase in voltage will result in an increase in current. Therefore, the current in the circuit will increase.
(iii) Complete the sentence to describe current in metals.
Current in metals is due to the flow of ……
▶️Answer/Explanation
electrons. In metals, electric current is due to the flow of free electrons, which are negatively charged particles.
Question 10 (Sub-topic: B19.1)
(a) The graph in Fig. 10.1 shows the area of land cleared by deforestation in one country between 2000 and 2010.
(i) Describe the pattern in the results shown in Fig. 10.1. Include data in your answer.
▶️Answer/Explanation
The graph shows that the area of land cleared by deforestation increased from 2000 to 2004, reaching a peak of approximately 27,000 hectares in 2004. After 2004, the area of land cleared decreased steadily, reaching around 7,000 hectares by 2009. The data indicates a significant reduction in deforestation after 2004.
(ii) Calculate the percentage decrease in the area of land cleared between 2008 and 2009.
▶️Answer/Explanation
To calculate the percentage decrease:
Area in 2008 = 12,000 hectares
Area in 2009 = 7,000 hectares
Decrease = 12,000 – 7,000 = 5,000 hectares
Percentage decrease = (5,000 / 12,000) × 100 = 41.67%
The percentage decrease in the area of land cleared between 2008 and 2009 is approximately 41.67%.
(b) Deforestation can cause a build-up of carbon dioxide in the atmosphere. Describe one way that humans directly increase the concentration of carbon dioxide in the atmosphere.
▶️Answer/Explanation
One way humans directly increase the concentration of carbon dioxide in the atmosphere is through the combustion of fossil fuels. When fossil fuels such as coal, oil, and natural gas are burned for energy, they release carbon dioxide as a byproduct, which contributes to the greenhouse effect and global warming.
(c) Many human activities create pollution which is harmful to the environment.
(i) The boxes on the left show some water pollutants. The boxes on the right show the sources of these pollutants.
Draw one line from each pollutant to its source.
▶️Answer/Explanation
Correct pairings:
- chemical waste → industries
- fertiliser → crop plant agriculture / farming
- rubbish (solid waste) → domestic / household waste
- untreated sewage → human and animal faeces
(ii) State one harmful effect of untreated sewage.
▶️Answer/Explanation
One harmful effect of untreated sewage is the spread of waterborne diseases such as cholera and dysentery. Untreated sewage contains harmful pathogens that can contaminate water sources, leading to outbreaks of disease in human populations.
Question 11 (Subtopic: C2.5)
Fig. 11.1 shows the structure of three molecules, ethene, ethanol and methane.
(a) State which of these molecules is not a hydrocarbon. Explain your answer.
(b) (i) Alkanes and alkenes are two different families of hydrocarbons.
Six hydrocarbons, L to Q, are listed below.
L butene
M dodecane
N hexane
O octane
P pentene
Q propane
Select from the letters L to Q the hydrocarbons that are alkenes.
(ii) Describe a chemical test that shows whether a hydrocarbon is an alkane or an alkene.
(c) Ethanol is made when ethene reacts at high temperatures with substance U in the presence of a catalyst.
(i) Identify substance U.
(ii) State the purpose of a catalyst in chemical reactions.
(d) Fig. 11.2 shows a process that produces an aqueous solution containing ethanol.
The gas given off causes limewater to turn milky.
(i) Name the process shown in Fig. 11.2.
(ii) Name the gas given off.
(iii) State a method that is used to separate ethanol from the aqueous solution.
▶️Answer/Explanation
(a) Ethanol is not a hydrocarbon because it contains oxygen, whereas hydrocarbons contain only carbon and hydrogen.
(b)(i) L and P are alkenes.
(b)(ii) Test: Add bromine water.
Result with an alkane: No change (remains orange).
Result with an alkene: Orange to colorless (bromine is decolourised).
(c)(i) Substance U is steam (H₂O).
(c)(ii) A catalyst increases the rate of a chemical reaction without being consumed in the process.
(d)(i) The process shown is fermentation.
(d)(ii) The gas given off is carbon dioxide.
(d)(iii) Distillation is used to separate ethanol from the aqueous solution.
Question 12
(a) Fig. 12.1 shows an electric heater containing three heating elements.
Fig. 12.2 shows how a heating element is made of metal wire wound around a ceramic rod.
(i) Describe what happens to the motion of the atoms in the solid metal wire as it increases in temperature. (Sub-topic: P2.1.2)
▶️Answer/Explanation
The atoms in the metal wire vibrate more vigorously as the temperature increases due to the gain in kinetic energy.
Explanation: As the temperature of the metal wire increases, the atoms in the solid metal wire vibrate more vigorously. This increased vibration is due to the atoms gaining kinetic energy from the heat, causing them to move more rapidly within their fixed positions in the lattice structure.
(ii) Explain why the metal wire is wound around a ceramic rod and not around a metal rod. (Sub-topic: P4.5.4)
▶️Answer/Explanation
The ceramic rod is used because it is an insulator, preventing a short circuit that would occur if a metal rod were used.
Explanation: The metal wire is wound around a ceramic rod because ceramic is an electrical insulator, whereas metal is a conductor. If the wire were wound around a metal rod, it could cause a short circuit, as the current would flow through the metal rod instead of the heating element. The ceramic rod prevents this by insulating the wire and ensuring that the current flows only through the heating element, allowing it to heat up properly.
(iii) State two methods of thermal energy transfer from the heater to a person in the room. (Sub-topic: P2.3)
▶️Answer/Explanation
Convection and radiation are the two methods of thermal energy transfer from the heater to a person in the room.
Explanation: Two methods of thermal energy transfer from the heater to a person in the room are:
- Convection: The heater warms the air around it, causing the air to rise and circulate, transferring heat to the person.
- Radiation: The heater emits infrared radiation, which travels through the air and is absorbed by the person, warming them.
(b) The heater is plugged into an extension socket along with other appliances. (Sub-topic: P4.4)
Fig. 12.3 shows the extension socket plugged into a single socket which is connected to the mains supply.
(i) Identify two electrical hazards in Fig. 12.3.
▶️Answer/Explanation
Overloaded socket and damaged cable are the two electrical hazards identified in Fig. 12.3.
Explanation: Two electrical hazards in Fig. 12.3 are:
- Overloaded socket: The extension socket is connected to multiple appliances, which could draw more current than the socket is designed to handle, leading to overheating and potential fire hazards.
- Damaged cable: The insulation on the cable to the electric heater appears to be damaged, which could expose the wires and lead to electric shocks or short circuits.
(ii) The plug for the heater requires a new fuse.
The current through the heater is 10A in normal use.
Four different fuse ratings are available.
3A 10A 13A 30A
State the most appropriate fuse rating.
▶️Answer/Explanation
The most appropriate fuse rating is 13A.
Explanation: The most appropriate fuse rating for the heater is 13A. This is because the fuse should be rated slightly higher than the normal operating current to allow for small surges in current without blowing, but not so high that it fails to protect the circuit in case of a fault.
(iii) State the purpose of a fuse in an electrical appliance.
▶️Answer/Explanation
The fuse protects the appliance and circuit by breaking the circuit if the current exceeds a safe level.
Explanation: The purpose of a fuse in an electrical appliance is to protect the appliance and the electrical circuit from excessive current. If the current exceeds a safe level, the fuse will blow, breaking the circuit and preventing damage to the appliance or potential fire hazards.
(c) The heater emits visible light and infrared radiation.
(i) Place visible light and infrared in their correct positions in the incomplete electromagnetic spectrum in Fig. 12.4. (Sub-topic: P3.3)
▶️Answer/Explanation
Visible light is in the middle box, and infrared is in the fifth box of the electromagnetic spectrum.
Explanation: In the electromagnetic spectrum, visible light should be placed in the middle box, and infrared should be placed in the fifth box. The order of the electromagnetic spectrum from left to right is: gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, and radio waves.
(ii) Each part of the electromagnetic spectrum has a different frequency.
In terms of waves, state the meaning of the term frequency. (Sub-topic: P3.1)
▶️Answer/Explanation
Frequency is the number of wave cycles passing a fixed point per unit of time, measured in hertz (Hz).
Explanation: Frequency, in terms of waves, refers to the number of wave cycles that pass a fixed point per unit of time. It is typically measured in hertz (Hz), where 1 Hz equals one wave cycle per second.
(d) Two heating elements are connected in series.
Each heating element has an electrical resistance of 6 Ω.
Calculate the combined resistance of the two heating elements. (Sub-topic: P4.3.2)
▶️Answer/Explanation
The combined resistance of the two heating elements is 12 Ω.
Explanation: When two resistors are connected in series, their resistances add up. Therefore, the combined resistance \( R_{\text{total}} \) is:
\[ R_{\text{total}} = R_1 + R_2 \]
Given that each heating element has a resistance of 6 Ω:
\[ R_{\text{total}} = 6 \, \Omega + 6 \, \Omega = 12 \, \Omega \]