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Question 1

Plant nutrition needs light and water.

Which row shows what else needs to be taken in?

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B6.1: Photosynthesis — nitrate ions (for amino acids) and carbon dioxide are also needed, alongside light and water.

▶️ Answer/Explanation

Photosynthesis requires carbon dioxide (raw material) along with light and water.
Nitrate ions are also absorbed by roots, needed for making amino acids/proteins, but not organic compounds directly.
✅ Answer: (C)

Question 2

The diagram shows a cell starting to plasmolyse.

In which direction is osmosis occurring?

A. X to Y
B. Y to X
C. Y to Z
D. Z to Y

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B3.2: Osmosis — net movement of water from a region of higher (less negative) water potential to a region of lower (more negative) water potential.

▶️ Answer/Explanation

As the cell plasmolyses, water is leaving the cell and moving out towards the surrounding solution.
Water moves by osmosis from a region of higher water potential (inside the cell, Z) to a region of lower water potential (outside, Y).
✅ Answer: (D)

Question 3

Which chemical element is found in all proteins, but not in all carbohydrates or fats?

A. carbon
B. hydrogen
C. oxygen
D. nitrogen

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B4.1: Biological molecules — proteins contain carbon, hydrogen, oxygen and nitrogen (some also sulfur), while carbohydrates and fats contain only carbon, hydrogen and oxygen.

▶️ Answer/Explanation

Carbohydrates and fats contain only carbon, hydrogen and oxygen.
Proteins additionally contain nitrogen (in the amino groups of amino acids), which is absent from carbohydrates and fats.
✅ Answer: (D)

Question 4

The Pompeii worm lives in deep-sea hydrothermal vents where average temperatures are often as high as 68°C.

Which graph represents the activity of enzymes found in the Pompeii worm?

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B5.1: Enzymes — rate of reaction rises with temperature to an optimum, then falls sharply as the enzyme denatures.

▶️ Answer/Explanation

The Pompeii worm’s enzymes must have an optimum temperature around 68°C, much higher than typical enzymes.
The correct graph shows the rate of reaction rising to a peak near 68°C before falling sharply as the enzyme denatures.
✅ Answer: (B)

Question 5

A plant has leaves which have white parts and green parts. One of the leaves is partly covered by a piece of black card on both sides. The plant is left in the light for two days.

The leaf is then removed and tested for the presence of starch.

Which row is correct?

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B6.1: Photosynthesis — starch is only produced where both chlorophyll and light are present (green, uncovered areas).

▶️ Answer/Explanation

Starch is only made where chlorophyll (green pigment) and light are both present, so only the uncovered green area (Q) tests positive.
White areas (P, R) lack chlorophyll and the covered green area (S) lacks light, so all three test negative for starch.
✅ Answer: (C)

Question 6

What is assimilation?

A. the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells
B. the movement of digested food molecules through the wall of the intestine into the blood
C. the passing out of food that has not been digested, as faeces, through the anus
D. the taking of food and drink into the body through the mouth

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B7.2: Digestive system — assimilation is defined as the uptake and use of nutrients by cells.

▶️ Answer/Explanation

Assimilation is the uptake and use of absorbed nutrients by the body’s cells, where they become part of the cell or are used for energy.
Option B describes absorption, C describes egestion, and D describes ingestion.
✅ Answer: (A)

Question 7

The diagram shows a plant shoot that is ringed. This removes the phloem from a section of the shoot.

The plant is left in bright light for 24 hours. Plant tissues are then tested for the presence of sucrose above the ringed section at P and below the ringed section at Q.

Which row shows the expected results?

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B8.4: Translocation — sucrose is transported in the phloem from the leaves (source) downward; removing phloem blocks this flow.

▶️ Answer/Explanation

Sucrose made by the leaves is translocated in the phloem downward through the shoot.
Since the ring removes the phloem, sucrose accumulates above the ring (at P) but cannot pass below it (absent at Q).
✅ Answer: (C)

Question 8

The diagram shows the main structures in the breathing system of humans.

Which row identifies the larynx, bronchus, trachea and bronchioles?

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B11.1: Gas exchange in humans — identifying larynx, trachea, bronchus and bronchioles from a diagram of the breathing system.

▶️ Answer/Explanation

Air passes in sequence from the larynx (S) into the trachea (R), which branches into the bronchus (P), then into the smaller bronchioles (Q).
Matching each label to its correct structure gives larynx = S, bronchus = P, trachea = R, bronchioles = Q.
✅ Answer: (C)

Question 9

The diagram shows a section through the skin.

Which labelled structures help to maintain body temperature in the cold?

A. 1 and 3
B. 1 and 4
C. 2 and 3
D. 3 and 4

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B13.3: Homeostasis — in cold conditions, vasoconstriction and shivering (skeletal muscle) help conserve/generate heat.

▶️ Answer/Explanation

In the cold, blood vessels near the skin surface constrict (vasoconstriction), reducing heat loss from the skin.
Skeletal muscles also contract rapidly (shivering) to generate extra heat through respiration.
✅ Answer: (A)

Question 10

Which statements correctly describe the human male gamete?

contains enzymes
food stores present
flagellum present
surrounded by a jelly coating

A. 1 and 2
B. 1 and 3
C. 2 and 3
D. 3 and 4

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B15.4: Sexual reproduction in humans — sperm structure: acrosome (enzymes) for penetrating the egg, and a flagellum (tail) for swimming.

▶️ Answer/Explanation

Sperm cells contain enzymes in the acrosome (head) to help penetrate the egg’s membrane at fertilisation.
They also have a flagellum (tail) that allows them to swim towards the egg; food stores and a jelly coating are features of egg cells, not sperm.
✅ Answer: (B)

Question 11

The table gives statements about a human haploid nucleus.

Which row is correct?

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B16.1: Chromosomes and genes — a haploid nucleus contains a single, unpaired set of chromosomes and is found in gametes, produced by meiosis (not mitosis).

▶️ Answer/Explanation

A haploid nucleus does have a single set of unpaired chromosomes and is found in gametes — both true statements.
However, gametes are produced by meiosis, not mitosis, so the third statement is false.
✅ Answer: (B)

Question 12

What is the main factor which determines the number of trophic levels in food chains?

A. competition between organisms
B. efficiency of energy transfer between trophic levels
C. removal of a member of a food chain
D. unstable ecosystem due to changing environment

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B18.2: Food chains and food webs — energy is lost at each trophic level, limiting the number of levels a food chain can support.

▶️ Answer/Explanation

Energy is lost as heat, in waste, and through respiration at every trophic level, so only a small percentage passes to the next level.
This inefficiency of energy transfer means there is eventually too little energy left to support another trophic level, limiting chain length.
✅ Answer: (B)

Question 13

Which row shows an effect of a human activity on the environment?

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B19.1: Habitat destruction — overuse of fertilisers causes nutrient run-off into waterways, leading to eutrophication.

▶️ Answer/Explanation

Cutting down forests is linked to reduced biodiversity and increased atmospheric carbon dioxide, not acid rain or eutrophication directly.
Overuse of fertilisers causes excess nitrates/phosphates to run off into water bodies, causing eutrophication.
✅ Answer: (D)

Question 14

Substance P is separated into different parts using simple physical techniques. Substance Q is only separated into simpler parts using chemical processes. Substance R is not separated into simpler parts by either physical or chemical processes.

Which type of substance are P, Q and R?

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C2.1: Elements, compounds and mixtures — distinguishing mixtures, compounds and elements by how they can (or cannot) be separated.

▶️ Answer/Explanation

A mixture (P) can be separated by simple physical methods like filtration or distillation, since its components are not chemically bonded.
A compound (Q) requires a chemical process to break the bonds between its elements, while an element (R) cannot be broken down further at all.
✅ Answer: (D)

Question 15

Hydrogen chloride is a gas. It dissolves in water to form an acidic solution.

Three different samples of hydrogen chloride are listed.

73.0 g of hydrogen chloride gas
7.30 dm³ of hydrogen chloride gas at r.t.p.
730 cm³ of 1.00 mol/dm³ aqueous hydrogen chloride

Which row shows the relative number of moles of hydrogen chloride in these samples?

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C3.3: The mole and the Avogadro constant — calculating moles from mass, gas volume at r.t.p., and solution concentration.

▶️ Answer/Explanation

Sample 1: (\text{moles} = \frac{73.0}{36.5} = 2.0) mol (M_r of HCl = 36.5).
Sample 2: (\text{moles} = \frac{7.30}{24} \approx 0.30) mol; Sample 3: (\text{moles} = 1.00 \times 0.730 = 0.730) mol.
Ordering fewest to most: sample 2 (0.30) < sample 3 (0.73) < sample 1 (2.0).
✅ Answer: (C)

Question 16

Aluminium is extracted from aluminium oxide by electrolysis.

What is added to aluminium oxide in this process?

A. concentrated aqueous sodium chloride
B. cryolite
C. dilute sulfuric acid
D. water

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C9.6: Extraction of metals — cryolite is added to lower the melting point of aluminium oxide during electrolysis.

▶️ Answer/Explanation

Pure aluminium oxide has a very high melting point (over 2000°C), which would be too costly to melt on its own.
Cryolite is added because it dissolves the aluminium oxide and lowers the operating temperature needed for electrolysis, saving energy.
✅ Answer: (B)

Question 17

Which statements about the reduction of copper(II) oxide by heating with carbon are correct?

Copper(II) ions lose electrons.
Copper(II) oxide acts as an oxidising agent.
Copper(II) oxide loses oxygen.
Oxide ions are reduced.

A. 1 and 2
B. 1 and 4
C. 2 and 3
D. 3 and 4

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C6.3: Redox — copper(II) oxide is reduced (loses oxygen) and acts as the oxidising agent, while carbon is oxidised.

▶️ Answer/Explanation

Copper(II) oxide loses oxygen to carbon (reduction), so statement 3 is correct; because it supplies oxygen for this reaction, it also acts as the oxidising agent (statement 2).
Copper(II) ions actually gain electrons (are reduced) as they form copper metal, so statement 1 is incorrect; oxide ions are not reduced, they combine with carbon to form CO₂, so statement 4 is also incorrect.
✅ Answer: (C)

Question 18

Copper carbonate is insoluble in water.

Which method can be used to make copper carbonate?

A. adding aqueous sodium carbonate to aqueous copper sulfate and filtering off the product
B. adding solid calcium carbonate to aqueous copper sulfate and filtering off the product
C. adding solid copper oxide to solid calcium carbonate and heating the mixture
D. heating copper metal in carbon dioxide

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C7.3: Preparation of salts — insoluble salts are made by precipitation, mixing two soluble solutions and filtering.

▶️ Answer/Explanation

Copper carbonate, an insoluble salt, is prepared by precipitation: mixing two soluble solutions whose ions combine to form the insoluble product.
Mixing aqueous sodium carbonate with aqueous copper sulfate produces insoluble copper carbonate, which is separated by filtration.
✅ Answer: (A)

Question 19

Which test and its result identifies aqueous bromide ions?

A. adding acidified aqueous silver nitrate forming a cream precipitate
B. adding acidified aqueous silver nitrate forming a white precipitate
C. adding aluminium foil and heating with sodium hydroxide forming a gas that turns red litmus paper blue
D. adding dilute acid forming a gas that produces a white precipitate when bubbled through limewater

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C12.5: Identification of ions and gases — acidified silver nitrate gives a cream precipitate with bromide ions (white with chloride, yellow with iodide).

▶️ Answer/Explanation

Adding acidified aqueous silver nitrate to a solution containing bromide ions forms an insoluble silver bromide precipitate.
This precipitate is characteristically cream in colour, distinguishing bromide (cream) from chloride (white) and iodide (yellow).
✅ Answer: (A)

Question 20

Which row about the trends in the elements going down Group I of the Periodic Table is correct?

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C8.2: Group I properties — reactivity increases down the group while melting point decreases.

▶️ Answer/Explanation

Going down Group I, the outer electron is further from the nucleus and more easily lost, so reactivity increases.
At the same time, the metallic bonding becomes weaker as atoms get larger, so melting point decreases down the group.
✅ Answer: (C)

Question 21

An airship containing an unreactive gas floats in air, as shown.

Which gas is used to fill the airship?

A. carbon dioxide
B. helium
C. hydrogen
D. nitrogen

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C8.5: Noble gases — helium is unreactive and less dense than air, making it safe for use in airships.

▶️ Answer/Explanation

The gas must float, so it needs to be less dense than air; it must also be unreactive for safety.
Helium is a noble gas that is unreactive and much less dense than air, making it ideal, unlike flammable hydrogen or denser gases like carbon dioxide and nitrogen.
✅ Answer: (B)

Question 22

Duralumin and magnalium are alloys used in the manufacture of aircraft. They both contain aluminium and another metallic element.

The alloys are made up of …1… of each element. They are used because they are …2… than the pure metals.

Which words complete gaps 1 and 2?

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C9.3: Alloys and their properties — alloys are mixtures of atoms of different sizes, making them harder than the pure metals.

▶️ Answer/Explanation

Alloys are made of atoms (not molecules) of different elements mixed together, since metals consist of atoms held by metallic bonding.
The different-sized atoms disrupt the regular layers of a pure metal lattice, preventing layers sliding easily, so alloys are harder than the pure metals.
✅ Answer: (A)

Question 23

Iron is extracted in the blast furnace.

Which reactions are involved in removing acidic impurities as slag?

(\text{C} + \text{O}_2 \rightarrow \text{CO}_2)
(\text{C} + \text{CO}_2 \rightarrow 2\text{CO})
(\text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2)
(\text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2)
(\text{CaO} + \text{SiO}_2 \rightarrow \text{CaSiO}_3)

A. 1 and 2 only
B. 1, 2 and 3
C. 3, 4 and 5
D. 4 and 5 only

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C9.6: Extraction of metals — limestone decomposes to calcium oxide, which reacts with silica (acidic impurity) to form slag.

▶️ Answer/Explanation

Reactions 1, 2 and 3 concern the reduction of iron oxide to iron using carbon and carbon monoxide, not the removal of acidic impurities.
Reactions 4 and 5 show limestone decomposing to calcium oxide, which then reacts with acidic silica (sand) impurity to form calcium silicate (slag).
✅ Answer: (D)

Question 24

Which statements about the reactions in a catalytic converter are correct?

The catalyst needs to be hot for the reactions to work.
Carbon dioxide is converted to carbon monoxide.
It converts pollutant gases into gases present in clean air.
Nitrogen and oxygen combine to form nitrogen monoxide.

A. 1 and 2
B. 1 and 3
C. 2 and 4
D. 3 and 4

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C10.2: Air quality and climate — catalytic converters convert pollutant gases (CO, NOx, unburnt hydrocarbons) into cleaner gases (CO₂, N₂, H₂O).

▶️ Answer/Explanation

The catalyst must be hot to operate effectively, and it converts harmful pollutant gases such as carbon monoxide and nitrogen oxides into cleaner gases like carbon dioxide and nitrogen.
Carbon dioxide is not converted into carbon monoxide (the reverse actually happens), and nitrogen monoxide is a pollutant formed in the engine, not deliberately formed by the converter.
✅ Answer: (B)

Question 25

Which substances neutralise acids?

lime
limestone
calcium hydroxide

A. 1 and 2 only
B. 1 and 3 only
C. 2 and 3 only
D. 1, 2 and 3

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C7.1: The characteristic properties of acids and bases — lime (CaO), limestone (CaCO₃) and calcium hydroxide are all bases that neutralise acids.

▶️ Answer/Explanation

Lime (calcium oxide) is a base and reacts with acids to form a salt and water.
Limestone (calcium carbonate) reacts with acids to form a salt, water and carbon dioxide, and calcium hydroxide (slaked lime) is also a base that neutralises acids.
✅ Answer: (D)

Question 26

Which statements about ethene and but-1-ene are correct?

Only ethene reacts with bromine water.
They are both formed by cracking alkanes.
They both react with steam to form alcohols.
They have different general formulae.

A. 1 and 2
B. 1 and 4
C. 2 and 3
D. 3 and 4

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C11.5: Alkenes — both ethene and but-1-ene are alkenes (general formula (C_nH_{2n})), formed by cracking and reacting with steam to form alcohols.

▶️ Answer/Explanation

Both ethene and but-1-ene are alkenes formed by cracking larger alkane molecules, so statement 2 is correct.
As alkenes with a C=C double bond, both add steam to form the corresponding alcohol, so statement 3 is also correct; both share the same general formula (C_nH_{2n}), and both decolourise bromine water, so statements 1 and 4 are false.
✅ Answer: (C)

Question 27

The flow chart shows some chemical substances and processes.

Which row identifies compound X and process Y?

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C11.6: Alcohols — fermentation of glucose with yeast produces ethanol, which burns (combustion) to give carbon dioxide and water.

▶️ Answer/Explanation

Fermentation of glucose solution with yeast produces compound X, which is ethanol, along with carbon dioxide.
Ethanol then undergoes process Y (combustion) to produce water and carbon dioxide, releasing energy.
✅ Answer: (A)

Question 28

An object falls freely in a vacuum.

Which speed–time graph represents the motion of the object?

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P1.2: Motion — free fall in a vacuum produces constant (uniform) acceleration, giving a straight line of increasing gradient on a speed–time graph.

▶️ Answer/Explanation

In a vacuum there is no air resistance, so the object experiences a constant acceleration due to gravity, (g).
A speed–time graph for constant acceleration from rest is a straight line through the origin with a positive, constant gradient.
✅ Answer: (D)

Question 29

An irregularly shaped object is lowered into a measuring cylinder of water.

As the object is lowered into the water, the water level rises from 50 cm³ to 75 cm³. The object has a mass of 50 g.

What is the density of the object?

A. 0.50 g/cm³
B. 0.67 g/cm³
C. 1.5 g/cm³
D. 2.0 g/cm³

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P1.4: Density — using water displacement to find volume, then calculating density as mass ÷ volume.

▶️ Answer/Explanation

The volume of the object equals the volume of water displaced: (75 – 50 = 25) cm³.
Density is calculated as (\rho = \frac{\text{mass}}{\text{volume}} = \frac{50}{25} = 2.0) g/cm³.
✅ Answer: (D)

Question 30

Which source of energy is non-renewable?

A. hydroelectric
B. nuclear fission
C. tides
D. waves

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P1.6.3: Energy resources — nuclear fuel is a finite resource, making nuclear fission non-renewable, unlike hydroelectric, tidal and wave power.

▶️ Answer/Explanation

Hydroelectric, tidal and wave power all rely on ongoing natural processes (water cycle, tides, wind/waves) that are continuously replenished.
Nuclear fission relies on a finite supply of uranium fuel, which is used up and cannot be replenished on a human timescale, making it non-renewable.
✅ Answer: (B)

Question 31

The diagram shows an object made partly of wood and partly of iron. Thermal energy is supplied in the position shown. Point P is marked at the bottom of the object.

How does most thermal energy reach point P?

A. by conduction through the iron
B. by conduction through the wood
C. by convection through the iron
D. by convection through the wood

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P2.3.1: Conduction — metals are good thermal conductors due to free (delocalised) electrons, transferring energy far faster than wood, a poor conductor/insulator.

▶️ Answer/Explanation

Solids transfer thermal energy by conduction, not convection, so options C and D can be ruled out immediately.
Iron is a good thermal conductor (due to its free/delocalised electrons) while wood is a poor conductor (insulator), so energy reaches P mainly by conduction through the iron.
✅ Answer: (A)

Question 32

Light undergoes total internal reflection in an optical fibre.

Which statement explains why this reflection occurs?

A. The angle of incidence is equal to the angle of refraction.
B. The angle of incidence is greater than the angle of reflection.
C. The angle of incidence is greater than the critical angle.
D. The angle of incidence is less than the critical angle.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P3.2.2: Refraction of light — total internal reflection occurs when the angle of incidence exceeds the critical angle.

▶️ Answer/Explanation

The critical angle is defined as the angle of incidence at which the angle of refraction is exactly 90°.
When the angle of incidence exceeds this critical angle, no light can be refracted out, so all of it is totally internally reflected back into the fibre.
✅ Answer: (C)

Question 33

Which statement about sound waves is not correct?

A. They are caused by vibrations.
B. They are longitudinal.
C. They transfer energy.
D. They travel in a vacuum.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P3.4: Sound — sound waves are longitudinal, caused by vibrations, transfer energy, but require a medium and cannot travel through a vacuum.

▶️ Answer/Explanation

Sound waves are longitudinal, are caused by vibrating sources, and transfer energy through a medium — statements A, B and C are all correct.
Unlike electromagnetic waves, sound needs a medium (solid, liquid, or gas) of particles to travel through, so it cannot travel through a vacuum.
✅ Answer: (D)

Question 34

A circuit contains a battery, a fixed resistor, an ammeter and a variable resistor.

The reading on the ammeter is 1.8 mA.

How much charge flows through the variable resistor in 30 s?

A. 0.054 C
B. 17 C
C. 54 C
D. 17 000 C

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P4.2.2: Electric current — using (Q = It) to calculate charge from current and time.

▶️ Answer/Explanation

In a series circuit, the same current (1.8 mA = 0.0018 A) flows through the variable resistor as through the ammeter.
Charge is calculated using (Q = It = 0.0018 \times 30 = 0.054) C.
✅ Answer: (A)

Question 35

A copper wire has a resistance of 8.0 Ω.

Four of these wires are arranged side by side to form a cable, as shown.

What is the resistance of this cable?

A. 0.50 Ω
B. 2.0 Ω
C. 32 Ω
D. 128 Ω

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P4.2.4: Resistance — four identical resistors side by side act as four equal resistors in parallel.

▶️ Answer/Explanation

Four wires side by side act as four equal resistors connected in parallel, so their combined resistance is lower than a single wire.
For (n) identical resistors in parallel, (R_{total} = \frac{R}{n} = \frac{8.0}{4} = 2.0) Ω.
✅ Answer: (B)

Question 36

The diagram shows a circuit containing a resistor and an NTC thermistor.

The temperature of the thermistor increases.

What happens to the resistance of the thermistor and what happens to the reading on the voltmeter?

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P4.2.4: Resistance — an NTC thermistor’s resistance decreases as temperature rises, changing the voltage shared across it.

▶️ Answer/Explanation

An NTC (negative temperature coefficient) thermistor’s resistance decreases as its temperature increases.
Since the thermistor’s share of the total resistance falls, the voltage dropped across it (read by the voltmeter across the thermistor) also decreases.
✅ Answer: (A)

Question 37

An electrical extension block has four sockets, a cable which can safely take a current of 6 A and a plug. It is protected by a fuse rated at 5 A.

The extension block is used with four appliances and the 5 A fuse blows. The owner replaces the 5 A fuse with a 13 A fuse.

Why is the extension block now dangerous?

A. The appliances may not receive enough current.
B. The cable may overheat before the fuse blows.
C. The sockets may burn out before the fuse blows.
D. The 13A fuse may blow too soon.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P4.4: Electrical safety — a fuse rating higher than the cable’s safe current limit fails to protect against overheating and fire risk.

▶️ Answer/Explanation

The cable is only rated to safely carry up to 6 A, but the 13 A fuse will not blow until the current exceeds 13 A.
This means a current between 6 A and 13 A could flow through the cable without the fuse cutting it off, causing the cable to overheat and potentially start a fire.
✅ Answer: (B)

Question 38

The diagram shows a wire in a magnetic field. There is a current in the wire in the direction shown. The direction of the magnetic field is also shown.

The magnetic field causes a force on the wire.

In which direction does this force act?

A. into the page
B. out of the page
C. towards the bottom of the page
D. towards the top of the page

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P4.5.4: Force on a current-carrying conductor — the direction of the force follows from the relative directions of current and magnetic field (left-hand rule).

▶️ Answer/Explanation

Using the relative directions of current, magnetic field and force (Fleming’s left-hand rule), the force on a current-carrying conductor is perpendicular to both the current and the field.
Applying this to the directions shown in the diagram gives a force acting into the page.
✅ Answer: (A)

Question 39

How do the ionising effect and the penetrating ability of alpha-emissions compare with those of beta-emissions?

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P5.2.2: The three types of nuclear emission — comparing the relative ionising effects and penetrating abilities of alpha and beta radiation.

▶️ Answer/Explanation

Alpha particles are large and heavily charged, so they interact strongly with matter, making them more ionising than beta particles.
Because they lose energy quickly through this strong interaction, alpha particles are also less penetrating than the smaller, faster beta particles.
✅ Answer: (B)

Question 40

A radioactive isotope has a half-life of 18 years. A sample contains 80 million atoms of this isotope.

How long does it take for the number of atoms of this isotope in the sample to decrease to 10 million?

A. 2.25 years
B. 6.0 years
C. 54 years
D. 180 years

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P5.2.4: Half-life — counting the number of half-lives needed for the atom count to fall from 80 million to 10 million.

▶️ Answer/Explanation

Each half-life halves the number of atoms: (80 \to 40 \to 20 \to 10) million, which takes 3 half-lives.
Total time = (3 \times 18 = 54) years.
✅ Answer: (C)