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=1Tf = \frac{1}{T} where TT is the period.
      • f=12.00=0.5extHzf = \frac{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=mghW = mgh
    • Where m=15extkgm = 15 ext{ kg}, g=9.81extm/s2g = 9.81 ext{ m/s}^2, h=3extmh = 3 ext{ m}, leads to
    • W=15imes9.81imes3=441.45extJW = 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=12mv2mgh = \frac{1}{2}mv^2
    • Thus, v=extsqrt(2gh)v = ext{sqrt}(2gh)
    • v = ext{sqrt}(2 imes 9.81 imes 3) ext{ m/s}
      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
      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^-
      ightarrow ext{Cu}

Question 8: Organic Compounds and Reactions

(a)
  1. Table Completion:
    • Examples:
      • Name: Butane
      • Structural Formula: C4H10C_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.