Question 1
(a) (i) Fig. 1.1 is a diagram of the alimentary canal and associated organs. (Sub-topic: B7.2)
State the letters in Fig. 1.1 that identify where:
- egestion occurs ……
- ingestion occurs ……
- saliva is produced ……
- water is absorbed. ……
▶️Answer/Explanation
- egestion occurs G
- ingestion occurs A
- saliva is produced B
- water is absorbed F / H
(ii) Name the organ labelled J in Fig. 1.1. (Sub-topic: B7.2)
▶️Answer/Explanation
liver
(iii) Name the organ labelled E in Fig. 1.1. (Sub-topic: B7.2)
▶️Answer/Explanation
pancreas
(b) A student has written an incorrect definition for digestion in a human. (Sub-topic: B7.3)
The definition the student has written is shown in Fig. 1.2.
Circle the two incorrect terms in the definition shown in Fig. 1.2.
▶️Answer/Explanation
oil (-soluble) and industrial should be circled.
(c) Table 1.1 shows some food molecules and the smaller molecules they are made from.
Complete Table 1.1.
| food molecules | smaller molecules |
|---|---|
| …… | fatty acids and glycerol |
| …… | amino acids |
| starch | …… |
▶️Answer/Explanation
| food molecules | smaller molecules |
|---|---|
| fats / oils | fatty acids and glycerol |
| protein | amino acids |
| starch | glucose |
Question 2 (Sub-topic: C9.5)
Metal oxides are formed when metals and oxygen react. Fig. 2.1 shows how magnesium oxide is formed.
(a)(i) The reaction releases thermal (heat) energy. State the term used to describe a chemical reaction that releases thermal energy.
▶️Answer/Explanation
Answer: Exothermic
Explanation: An exothermic reaction is a chemical reaction that releases energy in the form of heat. In this case, the formation of magnesium oxide from magnesium and oxygen releases thermal energy, making it an exothermic reaction.
(ii) Balance the symbol equation for the formation of magnesium oxide.
▶️Answer/Explanation
Answer: \(2Mg + O_2 \rightarrow 2MgO\)
Explanation: The balanced equation shows that two magnesium atoms react with one oxygen molecule to form two magnesium oxide molecules, ensuring the conservation of mass.
(b) Describe two physical properties of magnesium.
▶️Answer/Explanation
Answer: Magnesium is malleable and a good conductor of electricity.
Explanation: Magnesium is a metal that can be easily shaped (malleable) and allows the flow of electric current (good conductor). These properties are typical of many metals.
(c) Excess aqueous hydrochloric acid is added to magnesium and to magnesium oxide as shown in Fig. 2.2.
(i) Magnesium and magnesium oxide both react with aqueous hydrochloric acid. Describe one difference and one similarity in the observations made.
▶️Answer/Explanation
Answer: Difference: Gas is released with magnesium but not with magnesium oxide. Similarity: Both solids dissolve to form a soluble product.
Explanation: Magnesium reacts with hydrochloric acid to produce hydrogen gas, while magnesium oxide does not produce gas. However, both reactions result in the formation of a soluble product, magnesium chloride.
(ii) One of the products made in both reactions in (c)(i) is the same. State the name of this product.
▶️Answer/Explanation
Answer: Magnesium chloride (MgCl₂)
Explanation: Both magnesium and magnesium oxide react with hydrochloric acid to form magnesium chloride as the product.
(d) Aqueous hydrochloric acid is added to copper and to copper(II) oxide. There is no reaction between the hydrochloric acid and copper.
Copper(II) oxide reacts and dissolves in the acid.
(i) Explain why there is no reaction between copper and dilute acid. Use ideas about the relative positions of elements in the reactivity series.
▶️Answer/Explanation
Answer: Copper is less reactive than hydrogen.
Explanation: In the reactivity series, copper is below hydrogen, meaning it cannot displace hydrogen from acids. Therefore, copper does not react with dilute acids.
(ii) Predict whether the solution formed when copper(II) oxide reacts with the acid is coloured or is colourless. Explain your answer.
▶️Answer/Explanation
Answer: The solution is coloured.
Explanation: Copper(II) oxide reacts with acid to form copper(II) ions, which are typically blue or green in solution, indicating that the solution will be coloured.
(e) Rust is formed when iron reacts with oxygen and another substance.
(i) State the name of the other substance that must be present for iron to rust.
▶️Answer/Explanation
Answer: Water (or water vapour)
Explanation: Rusting of iron requires both oxygen and water. Without water, the reaction cannot proceed.
(ii) Barrier methods are used to prevent rusting. Name one substance used in the barrier method of rust prevention.
▶️Answer/Explanation
Answer: Paint
Explanation: Paint acts as a barrier, preventing oxygen and water from coming into contact with the iron, thus preventing rust.
(iii) State one way, other than forming a barrier, that prevents iron from rusting.
▶️Answer/Explanation
Answer: Making it into an alloy (e.g., stainless steel)
Explanation: Alloying iron with other metals, such as chromium, creates stainless steel, which is more resistant to rusting.
Question 3 (Sub-topic: P1.2)
(a) Fig. 3.1 shows a speed–time graph for a bus journey.
(i) Draw an X on the graph where the bus is not moving.
▶️Answer/Explanation
Solution:
The bus is not moving when the speed is 0 m/s. On the graph, this occurs at the points where the speed-time graph intersects the time axis (i.e., at t = 0 s and t = 160 s). Therefore, an X should be placed at these points.
X at (0,0) or (160,0)
(ii) Calculate the distance travelled by the bus in the first 60 s of the journey.
▶️Answer/Explanation
Solution:
The distance travelled can be calculated by finding the area under the speed-time graph for the first 60 seconds. The graph shows a triangle from 0 to 60 seconds with a base of 60 seconds and a height of 20 m/s.
The area of a triangle is given by:
\[ \text{Area} = \frac{1}{2} \times \text{base} \times \text{height} \]
Substituting the values:
\[ \text{Area} = \frac{1}{2} \times 60 \times 20 = 600 \text{ m} \]
Therefore, the distance travelled by the bus in the first 60 seconds is 600 meters.
600 m
(b) The bus has a mass of 5000 kg.
(i) Calculate the weight of the bus. The gravitational field strength g is 10 N / kg.
▶️Answer/Explanation
Solution:
The weight of an object is calculated using the formula:
\[ \text{Weight} = \text{mass} \times \text{gravitational field strength} \]
Given that the mass of the bus is 5000 kg and the gravitational field strength \( g \) is 10 N/kg:
\[ \text{Weight} = 5000 \times 10 = 50000 \text{ N} \]
Therefore, the weight of the bus is 50000 N.
50000 N
(ii) State the source of the gravitational field acting on the bus.
▶️Answer/Explanation
Solution:
The source of the gravitational field acting on the bus is the Earth.
Earth
(c) Fig. 3.2 shows the forces A, B, C and D as the bus moves forward at constant speed.
(i) Force B is increased. Describe how this affects the motion of the bus.
▶️Answer/Explanation
Solution:
If Force B is increased, the bus will accelerate because the resultant force acting on the bus will no longer be zero. The bus will start to move faster in the direction of the increased force.
The bus accelerates.
(ii) Force B is 500000 N. Force D is 100000 N. Calculate the resultant force of these two forces.
▶️Answer/Explanation
Solution:
The resultant force is calculated by subtracting Force D from Force B:
\[ \text{Resultant Force} = \text{Force B} – \text{Force D} = 500000 – 100000 = 400000 \text{ N} \]
Therefore, the resultant force is 400000 N.
400000 N
(d) The driver changes a wheel. Fig. 3.3 shows a wrench being used to loosen a wheel nut.
The driver applies a force of 1000 N on the wrench. Calculate the moment of this force on the wheel nut.
▶️Answer/Explanation
Solution:
The moment of a force is calculated using the formula:
\[ \text{Moment} = \text{Force} \times \text{Perpendicular Distance} \]
Given that the force applied is 1000 N and the perpendicular distance is 45 cm (which is 0.45 m):
\[ \text{Moment} = 1000 \times 0.45 = 450 \text{ Nm} \]
Therefore, the moment of the force on the wheel nut is 450 Nm.
450 Nm
Question 4 (Sub-topic: B11.1)
A scientist investigates the recovery time of an athlete and a non-athlete after exercise. Recovery time is the time taken for the pulse rate to return to normal after exercise.
The results are shown in Fig. 4.1.
(a)(i) State the pulse rate of the non-athlete at rest.
▶️Answer/Explanation
Answer: 72 bpm
Detailed Solution:
(a)(i) The pulse rate of the non-athlete at rest is 72 bpm. This is determined by observing the point on the graph where the non-athlete’s pulse rate is at its lowest before exercise begins.
(ii) State the length of recovery time for the athlete and the non-athlete.
▶️Answer/Explanation
Answer: Athlete: 3 minutes, Non-athlete: 7 minutes
Detailed Solution:
(a)(ii) The recovery time for the athlete is 3 minutes, and for the non-athlete, it is 7 minutes. This is calculated by measuring the time it takes for each individual’s pulse rate to return to their resting rate after exercise.
(iii) Calculate the difference in recovery times between the athlete and the non-athlete using your answers to (a)(ii).
▶️Answer/Explanation
Answer: 7 – 3 = 4 minutes
Detailed Solution:
(a)(iii) The difference in recovery times between the athlete and the non-athlete is 4 minutes. This is calculated by subtracting the athlete’s recovery time (3 minutes) from the non-athlete’s recovery time (7 minutes).
(iv) Describe the changes to the pattern of breathing of the non-athlete between 4 and 8 minutes.
▶️Answer/Explanation
Answer: The breathing rate would increase, and the breathing depth would increase.
Detailed Solution:
(a)(iv) Between 4 and 8 minutes, the non-athlete’s breathing rate and depth increase. This is because the body requires more oxygen to recover from the exercise and to remove the buildup of carbon dioxide.
(b) During exercise there is increased blood flow through the blood vessels. Fig. 4.2 is a photomicrograph of a cross‑section through an artery.
(i) State one piece of evidence from Fig. 4.2 that shows this blood vessel is an artery.
▶️Answer/Explanation
Answer: Thick wall
Detailed Solution:
(b)(i) The thick wall of the blood vessel is evidence that it is an artery. Arteries have thicker walls compared to veins to withstand the higher pressure of blood being pumped from the heart.
(ii) Name one component of blood visible in Fig. 4.2.
▶️Answer/Explanation
Answer: Red blood cell
Detailed Solution:
(b)(ii) One component of blood visible in Fig. 4.2 is the red blood cell. Red blood cells are responsible for carrying oxygen from the lungs to the rest of the body.
(c) The heart is responsible for pumping blood around the body.
(i) Name the structure that separates the right and the left sides of the heart.
▶️Answer/Explanation
Answer: Septum
Detailed Solution:
(c)(i) The structure that separates the right and left sides of the heart is called the septum. The septum ensures that oxygen-rich and oxygen-poor blood do not mix.
(ii) Name the type of tissue the walls of the heart are made from.
▶️Answer/Explanation
Answer: Muscular tissue
Detailed Solution:
(c)(ii) The walls of the heart are made from muscular tissue. This muscular tissue allows the heart to contract and pump blood throughout the body.
Question 5
Thermal decomposition happens when compounds are heated and break down into simpler substances.
(a) Limestone thermally decomposes to produce lime in a lime kiln.
Fig. 5.1 shows a lime kiln.
(i) State the chemical names of limestone and lime. (Sub-topic: C9.6)
▶️Answer/Explanation
Limestone: calcium carbonate
Lime: calcium oxide
(ii) Suggest why the limestone and carbon inside the lime kiln are in small pieces. (Sub-topic: C6.2)
▶️Answer/Explanation
The limestone and carbon are in small pieces to increase the surface area, which speeds up the reaction rate by allowing more contact between the reactants.
(iii) Explain why farmers often treat soil with limestone. (Sub-topic: C10.1)
▶️Answer/Explanation
Farmers treat soil with limestone to neutralize acidic soil, improving soil quality and making it more suitable for plant growth.
(b) Fig. 5.2 shows apparatus used for the thermal decomposition of sodium hydrogencarbonate.
When the sodium hydrogencarbonate in the test-tube is heated for several minutes, the following observations are made:
- A gas is released that turns limewater milky.
- The cobalt chloride paper changes colour from blue to pink.
- A different compound, sodium carbonate, remains in the test-tube.
(i) Use this information to complete the word equation for the thermal decomposition of sodium hydrogencarbonate. (Sub-topic: C6.1)
▶️Answer/Explanation
sodium hydrogencarbonate → sodium carbonate + carbon dioxide + water
(ii) The mass of sodium carbonate that remains after the reaction is smaller than the original mass of sodium hydrogencarbonate. (Sub-topic: C3.2)
Explain why.
▶️Answer/Explanation
The mass of sodium carbonate is smaller because gaseous products (carbon dioxide and water) are released during the reaction, reducing the total mass of the solid residue.
(c) Cracking of hydrocarbons is another example of thermal decomposition.
Fig. 5.3 shows the cracking of hydrocarbons.
(i) Both X and Y in Fig. 5.3 are mixtures of hydrocarbons. (Sub-topic: C11.5)
Describe two ways in which molecules in mixture X are different from molecules in mixture Y.
▶️Answer/Explanation
1. Mixture Y contains unsaturated hydrocarbons (and X does not).
2. Molecules in mixture Y are smaller on average than those in mixture X.
(ii) Predict the change in colour, if any, when mixture Y is shaken with aqueous bromine. (Sub-topic: C11.5)
▶️Answer/Explanation
The colour will change from orange to colourless.
Question 6
(a) A car is driven along a road.
(i) State the type of energy the car has due to its motion. (Sub-topic: P1.6.1)
▶️Answer/Explanation
Kinetic energy
(ii) During the journey, the car becomes electrostatically charged.
State what has been added to or removed from the car for it to become charged. (Sub-topic: P4.2.1)
▶️Answer/Explanation
Electrons
(iii) After the journey, the car needs to be refuelled at a gasoline (petrol) station.
State the type of energy stored in the fuel. (Sub-topic: P1.6.1)
▶️Answer/Explanation
Chemical potential energy
(iv) Not all of the energy stored in the fuel is transferred to the forward motion of the car.
Explain why this is. (Sub-topic: P1.6.1)
▶️Answer/Explanation
Energy is transferred to other forms, such as thermal energy due to friction and sound energy, and is lost to the surroundings.
(b) An electric car may be recharged by solar cells. (Sub-topic: P1.6.3)
Complete the sentences to describe how a solar cell can provide energy.
Light energy from the …… is absorbed by the solar cell.
The solar cell changes the light energy to …… energy.
▶️Answer/Explanation
Light energy from the Sun is absorbed by the solar cell.
The solar cell changes the light energy to electrical energy.
(c) The electric car has a powerful d.c. motor. (Sub-topic: P4.5.5)
The turning effect of the motor can be increased by increasing the number of turns on the coil in the motor.
State one other way to increase the turning effect of the d.c. motor.
▶️Answer/Explanation
Increase the strength of the magnetic field or increase the current.
(d)(i) The two headlamps of the car are powered by the car battery. (Sub-topic: P4.3.2)
The lamps are connected in parallel.
Complete the circuit diagram in Fig. 6.1 to show the two lamps connected in parallel, both controlled by one switch.
The battery has been drawn for you.
▶️Answer/Explanation
The circuit diagram should show the two lamps connected in parallel, with one switch controlling both lamps. The battery should be connected to the parallel circuit.
(ii) State one advantage of connecting the lamps in parallel. (Sub-topic: P4.3.2)
▶️Answer/Explanation
If one lamp fails, the other will still light up.
Question 7 (Sub-topic: B7.2)
(a) A student investigates the changes to plant cells when they are immersed in different concentrations of sugar solutions.
Fig. 7.1 shows a plant cell before immersion in a sugar solution.
Fig. 7.2 shows the concentrations of the sugar solutions used and the appearance of the cells after immersion.
(i) On Fig. 7.2, draw lines to link each concentration of sugar solution to the final appearance of the plant cell.
(ii) Suggest which plant cell, A, B, C or D, was placed in a solution of the same concentration as the plant cell.
▶️Answer/Explanation
(i) The lines should be drawn as follows:
- No sugar – B
- Low – A
- Medium – D
- High – C
(ii) The plant cell that was placed in a solution of the same concentration as the plant cell is A.
(b) The change in appearance of the plant cells is caused by osmosis.
Describe the process of osmosis.
▶️Answer/Explanation
Osmosis is the movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) through a partially permeable membrane. This process does not require energy and is a passive transport mechanism.
(c) Water and carbon dioxide are the raw materials needed for photosynthesis.
(i) State two other requirements needed for photosynthesis.
(ii) Complete the flowchart to show the pathway of water through a plant.
…… → root cortex cells → …… → mesophyll cells
▶️Answer/Explanation
(i) The two other requirements needed for photosynthesis are:
- Light
- Chlorophyll
(ii) The pathway of water through a plant is:
- Root hair cells → root cortex cells → xylem → mesophyll cells
(d) Plants use photosynthesis to make their own nutrients.
State the term used to describe organisms that use photosynthesis to make their own nutrients.
▶️Answer/Explanation
The term used to describe organisms that use photosynthesis to make their own nutrients is producers.
Question 8
Electrolysis is used to extract some elements from their ores.
(a) Aluminium is extracted using electrolysis. State the name of the ore from which aluminium is extracted. (Sub-topic: C4.1)
▶️Answer/Explanation
Answer: Bauxite
(b) Use words from the list to complete the sentences about electrolysis. Each word may be used once, more than once or not at all. (Sub-topic: C4.1)
boiling chemical current electron evaporation
melting physical reacting resistance voltage
In electrolysis, an electric …………. passes through an electrolyte. The electrolyte is made either by dissolving a compound in water or by …………. it. Electrolysis is an example of a …………. change.
▶️Answer/Explanation
Answer: current; melting; chemical
(c) Fig. 8.1 shows three sets of apparatus, Q, R and S, that a student uses to investigate electrolysis. Each beaker contains aqueous solutions of different compounds.
All of the electrodes are inert. (Sub-topic: C4.1)
Table 8.1 shows the observations the student makes.
(i) Suggest the compound that is dissolved to form the electrolyte in apparatus Q.
▶️Answer/Explanation
Answer: Sodium chloride / other correct compound
(ii) Suggest a reason why the solution in apparatus R does not conduct.
▶️Answer/Explanation
Answer: The liquid is not an electrolyte / does not contain (free) ions / the compound dissolved is not ionic.
(iii) The electrolyte in apparatus S is an aqueous acid. Suggest the name of this acid. (Sub-topic: C4.1)
▶️Answer/Explanation
Answer: Sulfuric (acid) / other correct acid
(d) Atoms and ions contain protons and electrons. Protons and electrons are electrically charged particles. (Sub-topic: C2.2)
(i) Explain why a potassium atom is electrically neutral. Use ideas about the charges on the particles in your answer.
▶️Answer/Explanation
Answer: Reference to protons being positive and electrons being negative. In an atom, the number of protons and electrons is equal, so the charges cancel out, making the atom electrically neutral.
(ii) Explain why a potassium ion has an electrical charge of +1. Your answer should include:
- how a potassium ion is formed
- why it has a charge of +1.
▶️Answer/Explanation
Answer: A potassium ion is formed when a potassium atom loses one electron. Since the potassium atom originally had equal numbers of protons and electrons, losing one electron means there is one more proton than electrons, resulting in a net charge of +1.
Question 9 (Sub-topic: B18.1)
Beneath the surface of the Earth, solid rocks are heated and form liquid rock (magma) and gases.
(a) (i) On Fig. 9.1, draw lines to link each state of matter with the correct arrangement of particles.
▶️Answer/Explanation
Answer: Gas – particles far apart; Liquid – particles close together; Solid – particles in fixed positions.
(ii) In some places, the hot magma comes to the surface as lava. Some hot lava flows into water in a lake. A liquid-in-glass thermometer is used to measure the temperature of the water in the lake. The liquid in the thermometer rises as the water in the lake is heated. Explain why the liquid in the thermometer is able to show the increase in temperature.
▶️Answer/Explanation
Answer: The liquid in the thermometer expands as it absorbs thermal energy from the heated water, causing it to rise and indicate the increase in temperature.
(iii) A different thermometer has no scale on it. Describe how melting ice and boiling water can be used to identify fixed points on this thermometer.
▶️Answer/Explanation
Answer: Melting ice can be used to mark the 0°C point, and boiling water can be used to mark the 100°C point. These fixed points help in calibrating the thermometer.
(b) People standing near the hot lava feel the thermal energy being emitted by infrared radiation. On Fig. 9.2, place infrared radiation in the correct place on the incomplete electromagnetic spectrum.
▶️Answer/Explanation
Answer: Infrared radiation should be placed between visible light and microwaves on the electromagnetic spectrum.
(c) A cooled sample of lava is tested for radioactivity. Describe how a radiation detector is used to determine if α-particles are being emitted.
▶️Answer/Explanation
Answer: A radiation detector, such as a Geiger-Muller tube, is used to detect α-particles. The detector measures the ionizing radiation emitted by the sample, and if α-particles are present, they will cause a noticeable increase in the count rate.
(d) The lava contains the isotope potassium-40. The nuclide notation is \( _{19}^{40}\textrm{K}\).
State the number of protons and neutrons in the nucleus of potassium-40.
▶️Answer/Explanation
Answer: Number of protons = 19; Number of neutrons = 21.
Question 10 (Sub-topic: B13.1)
(a) Complete the sentences about the nervous system using words from the list.
Each word may be used once, more than once or not at all.
backbone brain chemical electrical nerve peripheral
There are two parts to the human nervous system. The central nervous system and the …… nervous system.
The central nervous system consists of the …… and the spinal cord.
Responses are coordinated by impulses, which are …… signals passed along …… cells called neurones.
▶️Answer/Explanation
Answer:
There are two parts to the human nervous system. The central nervous system and the peripheral nervous system.
The central nervous system consists of the brain and the spinal cord.
Responses are coordinated by impulses, which are electrical signals passed along nerve cells called neurones.
(b) Fig. 10.1 shows a type of neurone.
Identify the type of neurone shown in Fig. 10.1.
▶️Answer/Explanation
Answer:
The type of neurone shown in Fig. 10.1 is a sensory neurone.
(c) Hormones coordinate and regulate responses.
A hormone controls the response in shoots and roots in plants.
(i) Describe the response of the shoots and roots to gravity.
Include the name of the response in your answer.
▶️Answer/Explanation
Answer:
The response of shoots and roots to gravity is called gravitropism.
– Shoots exhibit negative gravitropism, meaning they grow away from the direction of gravity.
– Roots exhibit positive gravitropism, meaning they grow towards the direction of gravity.
(ii) Name one other stimulus that shoots and roots respond to.
▶️Answer/Explanation
Answer:
One other stimulus that shoots and roots respond to is light (phototropism).
Question 11 (Sub-topic: B16.1)
Carbon occurs as a free element in the Earth’s crust. Carbon also occurs in millions of different compounds.
(a) Fig. 11.1 shows the structures of two forms of carbon, A and B.
(i) State the names of these forms of carbon.
▶️Answer/Explanation
A: Diamond
B: Graphite
Detailed Solution:
11(a)(i): The two forms of carbon shown in Fig. 11.1 are diamond and graphite. Diamond has a tetrahedral structure where each carbon atom is bonded to four other carbon atoms, forming a rigid three-dimensional network. Graphite, on the other hand, has a layered structure where each carbon atom is bonded to three others, forming hexagonal rings. The layers are held together by weak van der Waals forces, allowing them to slide over each other.
(ii) State the type of chemical bonding and structure present in both A and B.
▶️Answer/Explanation
Type of bonding: Covalent
Type of structure: Giant
Detailed Solution:
11(a)(ii): Both diamond and graphite are composed of carbon atoms bonded together by strong covalent bonds. However, the type of structure differs: diamond has a giant covalent structure, while graphite also has a giant covalent structure but with layers that can slide over each other due to weak interlayer forces.
(b) The pie charts in Fig. 11.2 show the compositions of two gas mixtures, L and M.
(i) Gas mixture L is the fossil fuel, natural gas. Identify gas Q.
▶️Answer/Explanation
Gas Q: Methane (CH4)
Detailed Solution:
11(b)(i): Natural gas primarily consists of methane (CH4), which is a simple hydrocarbon. Methane is a major component of natural gas and is used as a fuel.
(ii) A student wants to distinguish between mixture L and mixture M. Describe a test he can do. Include the results in each case.
▶️Answer/Explanation
Test: Use damp red litmus paper.
Result with L: No reaction (remains red).
Result with M: Turns blue (indicating the presence of ammonia).
Detailed Solution:
11(b)(ii): To distinguish between natural gas (L) and a mixture containing ammonia (M), a simple test using damp red litmus paper can be performed. Ammonia is a basic gas and will turn damp red litmus paper blue, whereas natural gas (methane) is neutral and will not affect the litmus paper.
Question 12
(a) Fig. 12.1 shows a boy looking into a plane mirror. He can see the reflection of an apple. (Sub-topic: P3.2.1)
(i) Name the line XY shown on Fig. 12.1.
▶️Answer/Explanation
Answer: The line XY is called the normal.
Explanation: In optics, the normal is an imaginary line perpendicular to the surface of the mirror at the point where the light ray strikes the mirror. It is used to measure the angles of incidence and reflection.
(ii) On Fig. 12.1, draw the reflected ray to the boy and label with the words “reflected ray”.
▶️Answer/Explanation
Answer: The reflected ray should be drawn at the same angle as the incident ray but on the opposite side of the normal. Label it as “reflected ray”.
Explanation: According to the law of reflection, the angle of incidence is equal to the angle of reflection. The reflected ray should be drawn symmetrically to the incident ray with respect to the normal.
(iii) On Fig. 12.1, mark the angle of incidence and label with the letter i.
▶️Answer/Explanation
Answer: The angle of incidence is the angle between the incident ray and the normal. Mark this angle and label it as i.
Explanation: The angle of incidence is always measured between the incident ray and the normal, not the mirror surface.
(iv) Circle the two correct words or phrases that describe the image of the apple in the mirror.
diminished enlarged laterally inverted same size upside down
▶️Answer/Explanation
Answer: The correct words are laterally inverted and same size.
Explanation: In a plane mirror, the image formed is always the same size as the object and is laterally inverted (left and right are swapped). The image is not diminished, enlarged, or upside down.
(b) The boy takes a photograph of the apple using a digital camera with a thin converging lens as shown in Fig. 12.2. (Sub-topic: P3.2.3)
(i) On Fig. 12.2, draw a ray of light from the bottom of the apple to show where it will be detected on the image sensor of the camera.
▶️Answer/Explanation
Answer: Draw a ray from the bottom of the apple that passes through the lens and converges to a point on the image sensor.
Explanation: In a converging lens, light rays from the object converge to form an image on the image sensor. The ray from the bottom of the apple should pass through the lens and focus on the sensor.
(ii) On Fig. 12.2, draw a double-headed arrow (↔) to show the focal length of the lens.
▶️Answer/Explanation
Answer: Draw a double-headed arrow from the center of the lens to one of its focal points, labeling it as the focal length.
Explanation: The focal length is the distance from the center of the lens to its focal point, where parallel rays of light converge after passing through the lens.
(c) To improve the photograph, the boy uses the camera flash. The flash is a lamp operated by a cell and a switch. The current in the lamp is 0.5A. The voltage across the lamp is 6V. Calculate the resistance of the lamp. (Sub-topic: P4.2.4)
▶️Answer/Explanation
Answer: The resistance of the lamp is 12 Ω.
Explanation: Using Ohm’s Law, \( R = \frac{V}{I} \), where \( V = 6V \) and \( I = 0.5A \). Therefore, \( R = \frac{6}{0.5} = 12 \Omega \).