Examination Details

• Examination Body: Botswana Examinations Council in collaboration with University of Cambridge Local Examinations Syndicate
• Certificate: Botswana General Certificate of Secondary Education
• Paper: Science: Double Award Paper 3
• Centre Number: [to be filled in by candidates]
• Candidate Number: [to be filled in by candidates]
• Examination Date: October/November 2009
• Duration: 2 hours
• Instructions:
  • Candidates answer on the Question Paper.
  • Write in dark blue or black pen; soft pencil can be used for diagrams, graphs, or rough working.
  • Do not use staples, paper clips, highlighters, glue, or correction fluid.
  • Answer all questions and use space provided.
  • Periodic Table is printed on page 20.

Questions Overview

Question 1: Pendulum Mechanics

• Fig. 1.1: Diagram of a pendulum swinging to-and-fro about point A.
• Time for one complete swing: 2.00 seconds

(a)

1. Terms:
   • (i) One complete to-and-fro swing is known as one period.
   • (ii) Period of the pendulum: 2.00 s
   • (iii) Frequency Calculation:
     • Formula: f = rac{1}{T} where $T$ is the period.
     • f = rac{1}{2.00} = 0.5 ext{ Hz}

(b)

1. Effects on period:
   • (i) Increasing the mass of the bob: No effect on the period.
   • (ii) Decreasing the length of the string: Decreases the period; a shorter length results in increased frequency.

Question 2: Energy and Work Calculation

(a)

• Scenario: A boy with mass 15 kg slides down a slope of length 30 m and climbs 3 m vertically.

1. Work Done Calculation:
   • Work done to reach the top: $W = mgh$
   • Where $m = 15 ext{ kg}$, $g = 9.81 ext{ m/s}^2$, $h = 3 ext{ m}$, leads to
   • $W = 15 imes 9.81 imes 3 = 441.45 ext{ J}$

(b)

• Energy Change: The major energy change as the boy slides down the slope is from potential energy to kinetic energy.

(c)

1. Velocity Calculation:
   • Using conservation of energy, potential energy lost equals kinetic energy gained. At the bottom of the slope:
   • mgh = rac{1}{2}mv^2
   • Thus, $v = ext{sqrt}(2gh)$
   • $v = ext{sqrt}(2 imes 9.81 imes 3) ext{ m/s} <br /> ightarrow 7.75 ext{ m/s}$

Question 3: Heat Conductivity and Bimetallic Strips

(a)

1. Heat Conduction in Solids:
   • Solids conduct heat primarily through vibration of atoms and transfer of kinetic energy; particles in the solid lattice vibrate and collide, transferring heat.

(b)

1. Heating Iron and Copper Rods:
   • Increases/Decreases/Remains Constant for the following quantities:
     • Mass: Remains the same
     • Volume: Increases due to thermal expansion
     • Density: Decreases as mass remains constant while volume increases

(c)

1. Bimetallic Strip:
   • (i) Reason for Bending Upon Heating: Different thermal expansion rates of brass and copper cause bending.
   • (ii) Use of a Bimetallic Strip: Commonly used in thermostats.

Question 4: Alternating Current Generator

(a)

1. Parts of a Generator:
   • (i) Name parts X and Y from Fig. 4.1
   • X: Coil
   • Y: Magnet
   • (ii) Ways to Increase Output Voltage:
     • 1. Increase the number of turns in the coil.
     • 2. Increase the strength of the magnetic field.
   • (iii) Direction of Induced Current: Draw an arrow on the diagram indicating the direction.

(b)

1. Voltage Waveform:
   • Draw one complete cycle with maximum voltage 3V.

Question 5: Radiation and Particles

(a)

1. Background Radiation Definition:
   • Background radiation is the low-level ionizing radiation present in the environment. It originates from natural and artificial sources.

(b)

1. Particle Emission:
   • (i) Particle emitted with 2 protons and 2 neutrons is called an Alpha Particle.
   • (ii) Charge of the Emitted Particle: +2

(c)

1. Uses of Radioactive Substances:
   • 1. Medical imaging and treatment.
   • 2. Radiocarbon dating.

Question 6: Diffusion Experiment

(a)

1. Movement of Gases: Gases move by diffusion.

(b)

1. Relative Molecular Mass Calculation:
   • Calculate the relative molecular mass of ammonia (NH₃):
   • $N = 14, H = 1 imes 3 <br /> ightarrow 14 + 3 = 17$
   • (ii) Explanation of Gas Meeting Point: The position X is nearer to the hydrochloric acid because hydrogen chloride has a higher molecular mass (36.5) compared to ammonia (17), thus diffusing slower.
   • (iii) Color Change of Litmus Paper: Red litmus paper turns blue, indicating the presence of ammonia.
   • (iv) Use of Damp Litmus Papers: Damp litmus papers are used to ensure clear color change reactions occur, as dry ones may not react effectively.

(c)

1. Chlorine Reaction:
   • (i) Oxidized Substance: Iron (II) ions are oxidized to iron (III) ions.
   • (ii) Need for Fume Cupboard: Necessary to handle chlorine gas safely due to toxicity.

Question 7: Transition Metals and Electroplating

(a)

1. Properties of Transition Metals:
   • 1. Good conductors of heat and electricity.
   • 2. Ductility and malleability.

(b)

1. Graphite Form: Graphite is a form of carbon.
   • (ii) Another form: Diamond.
   • (iii) Reason for Graphite Coating: To improve conductivity for the electroplating process.

(c)

1. Electroplating Process:
   • (i) Anode Material: Copper.
   • (ii) Dissolution of Copper(II) Sulphate: Necessary to facilitate the movement of ions in the solution.
   • (iii) Formation of Copper Atoms:
   • $ext{Cu}^{2+} + 2e^- <br /> ightarrow ext{Cu}$

Question 8: Organic Compounds and Reactions

(a)

1. Table Completion:
   • Examples:
     • Name: Butane
     • Structural Formula: $C_4H_{10}$
     • Homologous Series: Alkanes
   • (ii) Isomer of Butane:
   • Structural Representation:
   • Example: 2-Methylpropane.

(b)

1. Addition Reaction Explanation: Ethene undergoes addition reaction due to the presence of a double bond, which opens up to form a single bond with hydrogen.
   • (ii) Conditions of Reaction and Reasons:
     • 1. Presence of a catalyst (nickel): To speed up the reaction.
     • 2. Moderate temperature (around 150°C): Facilitates better reaction rates.
   • (iii) Product of Reaction: Product formed is Ethane.

(c)

1. Polymerisation of Alkenes: Example of polymer: Polyethylene
   • Structure: (-CH₂-CH₂-) (repeating units).

Question 9: Water Chemistry

(a)

1. Substances From List:
   • (i) Substance used to sterilize water: Chlorine.
   • (ii) Unreactive Diatomic Molecule: Nitrogen (N₂).
   • (iii) Causes Temporary Hardness: Magnesium hydrogencarbonate.

(b)

1. Dot and Cross Diagram: Water molecule structure H₂O reveals two hydrogen atoms bonded to one oxygen atom.

Question 10: Mammalian Reproductive System

(a)

1. Fig. 10.1 Structure: Label structure X with Placenta.

(b)

1. Function of Structure Y: Provides attachment and nutrient transfer between the mother and the foetus.

(c)

1. Cross-section Blood Vessel Identification:
   • (i) Identify vein as “Blood Vessel Q”.
   • (ii) Reason: Veins have thinner walls than arteries, and valves are present.
   • (iii) Substances in High Concentration: Oxygen and Nutrients.

Question 11: Carbon Cycle

(a)

1. Name Process Y: Photosynthesis.

(b)

1. Additions of Carbon Dioxide Process: Respiration or combustion.

(c)

1. Identify Organism P: Plants.

(d)

1. Benefits from Process X: Provides oxygen, crucial for respiration.

Question 12: Transpiration Rates

(a)

1. Highest Transpiration Rate Time: At 1400 hours.
   • (ii) Humidity Influence: As humidity increases, transpiration rate decreases due to reduced moisture gradient.

(b)

1. Other Factors Affecting Transpiration:
   • 1. Wind speed: Increased wind can enhance transpiration.
   • 2. Temperature: Higher temperatures result in higher rates of transpiration.

Question 13: Biotechnology

(a)

1. Biotechnology Definition: Use of biological systems or organisms to develop or create products.

(b)

1. Breweries and Biotechnology: Commercial breweries use biotechnology to optimize fermentation processes, improving product yield and quality.

Question 14: Visking Tube Experiment

(a)

1. Identify Solutions in Tube:
   • Contents: Starch and glucose (assumed).

(b)

1. Explanation of Brick-red Color Change: The brick-red color indicates the presence of reducing sugars after diffusion through the semi-permeable visking tube.

(c)

1. Predicted Iodine Test Result:
   • Prediction: Negative Sample (yellow color indicating no starch).
   • Reason: Amylase breaks down starch into glucose, which does not change iodine color.
   • (ii) Similar Reaction Location: Occurs in the small intestine.

Question 15: Nervous System Response

(a)

1. Neurone Link in CNS: Interneuron.

(b)

1. Receptor and Effector in Action:
   • Receptor: Skin receptor (for heat).
   • Effector: Muscle (in arm to withdraw hand).

(c)

1. Transmission Mode Comparison: Nervous transmission is faster and more localized compared to hormonal transmission which is slower and widespread.