O Level – Combined Science

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  • #2987

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    Sound – Key Concepts

    1. Sound is produced by vibrating sources placed in a medium.

    2. A sound wave is an example of a longitudinal wave and comprises of a series of compressions and rarefactions in the medium.

    3. There are three types of graphs to describe sound waves i.e. pressure-distance graph, displacement-distance graph and displacement-time graph.

    4. Ultrasound are sound waves that have frequencies above 20 kHz.

    5. Some uses of ultrasound include quality control and prenatal scanning

    6. Pitch is a subjective quantity that is related to the objective quantity of frequency.

    7. Loudness is a subjective quantity that is related to the objective quantity of amplitude.

    8. Pitch is a subjective quantity that is related to the objective quantity of frequency.

    9. Loudness is a subjective quantity that is related to the objective quantity of amplitude.

    From O level Physics Tutor

    #2999

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    Electrostatic – Key Concepts I

    1. There are two types of charges—positive and negative.

    2. Like charges repel, unlike charges attract

    3. Charge is measured in coulombs (C).

    4. Electrostatic charging by friction involves a transfer of electrons.

    5. Electrical insulators (e.g. rubber) do not conduct electricity because their electric charges (electrons) are not free to move about.

    6. Electrical conductors (e.g. copper) are able to conduct electricity because their electric charges (electrons) are free to move within them.

    7. Charged insulators can be neutralised by heating and humid conditions.

    8. Conductors can be charged by induction.

    From O level Physics Tutor

    #3043

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    Electrostatic – Hazards and Applications of Electrostatics

    1. An electric field is a region where an electric charge experiences an electric force.

    2. The direction of the field is the direction of the force on a small positive charge.

    3. Some hazards of electrostatic charging are lightning and electrostatic discharge.

    4. Some uses of electrostatic charging are the laser printer, photocopier and electrostatic precipitators.

    From O level Physics Tutor

    #3067

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    Electrostatic – Key Concepts II

    Some hazards of electrostatics

    1. Lightning

    Thunderclouds are charged by friction between the water molecules in the thunderclouds and air molecules.

    It then ionises the air and the ionised air provides a conducting path for electric charge to be discharged to the nearest or sharpest object on the ground.

    2. Electrostatic discharge

    Excessive charges may build up due to friction. Sudden discharge may cause sparks and ignite flammable materials nearby

    Electronic equipment, such as computer boards and hard drive, can be easily damaged.

    Such equipments are usually packed in antistatic packaging materials.

    See movie : Static @ Petrol.

    Practical applications of electrostatics

    1. Laser printer

    2. Electrostatic precipitator

    3. Spray painting

    As the spray leaves the nozzle, the particles of paint become charged by friction.

    The paint particles contain like charges thus they spread out when they are sprayed on a car body.

    The charged paint particles will be attracted to the metallic car body.

    From O level Physics Tutor

    #3096

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    Misconception Analysis – Measurement

    Stop and Think, are the following questions True or False

    1. A Physical quantity must have both magnitude and unit.

    2. Base quantities and base units are the same.

    3. Derived quantities are not physical quantities.

    4. The SI units for length, mass and time are the metre, gram and second respectively .

    5. Prefixes are used to express big numbers only

    Ans TFFFF

    From O level Physics Tutor

    #3112

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    Misconception Analysis – Kinematics

    Stop and Think, are the following questions True or False

    1. Speed is defined as the rate of change of distance

    2. The gradient of a displacement-time graph at any point gives the average velocity

    3. The area under the velocity-time graph is the displacement

    4. When an object is moving, it must have acceleration.

    5. The SI unit for acceleration is ms^-2

    Ans TFTFT

    From O level Physics Tutor

    #3140

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    Misconception Analysis – Dynamics

    Stop and Think, are the following questions True or False

    1. A resultant force is needed to start a motion.

    2. A resultant force is needed to keep an object moving with constant velocity.

    3. When there is no resultant fore acting on an object, the object may be at rest.

    4. A resultant force will cause the object to move faster.

    5. According to Newton, forces always act in pairs

    Ans – TFTFT

    From O level Physics Tutor

    #3158

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    Misconception Analysis – Mass Weight and Density

    Stop and Think, are the following questions True or False

    1. Mass is always constant.

    2. Weight increases as mass increases.

    3. Weight cannot be measured by beam balance.

    4. Gravitational field strength is numerically equal to the acceleration due to gravity.

    5. An object with bigger mass has higher inertial than an object with smaller mass.

    Ans : TTFTT

    From O level Physics Tutor

    #3217

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    Measurement – Key Points

    1. Micrometer screw gauge has better precision than the vernier calipers. Its maximum reading is smaller than the vernier calipers, thus, if is only suitable for measuring small objects like diameter of wire.

    For more key points, please contact Mr Ong @9863 9633

    #3237

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    Key Points – Dynamics

    1. In solving kinematics questions. We can define motion to the right is positive or negative.
    All vectors quantities example displacement, velocity and acceleration in that direction will be positive.

    2. A ball thrown upwards will experience a constant acceleration of g during the upward and downward motion with air resistance neglected.

    For more key points and exam based questions with full worked solution, please contact Mr Ong @9863 9633

    #3267

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    Key Points – Forces

    F = ma
    F = resultant force acting on the body
    m = mass of the body
    a = acceleration of the body

    1. Zero resultant force does not imply that the body is stationary.

    2. If resultant force acting on the body is zero, it only implies that the acceleration of the body is zero.

    3. Zero acceleration only implies that velocity is constant.

    For more key points and exam based questions with full worked solution, please contact Mr Ong @9863 9633

    #3340

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    Chemical Bonding – Important Definitions

    1. An ion is a charged particle formed from an atom by loss or gain of electrons

    2. A cation is a positively charged ion formed when an atom loses valence electrons(s)

    3. An anion is a negatively charged ion formed when an atom gains valence electrons(s)

    4. A simple ion is an ion formed from single atoms eg Na+, A polyatomic ion is an ion containing more than one kind of atom eg NH4+ or SO42-

    5. An ionic bond is the strong electrostatic fore of attraction between positive and negative ions in an ionic compound.

    6. A covalent bond is the bond formed by sharing of electrons between two non-metal atoms.

    7. A molecule is a small group of atoms held together by covalent bonds.

    8. A metallic bond is the force of attraction between positive metal ions and the ‘sea of delocalised electrons’

    For more key points and exam based questions with full worked solutions please contact Mr Ong @98639833

    #3355

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    The Mole – Key Points

    1. Both relative atomic mass and relative molecular mass have no units.

    2. Empirical formula an molecular formula may or may not be the same.

    3. The total percentage composition of the elements in the compound must be 100%.

    4. 1 dm^3 = 1000 cm^3

    5. When calculating the Mr of a substance in the reaction, do not include the coefficient.

    For more key points and exam based questions with full worked solutions please contact Mr Ong @98639833

    #3394

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    Chemical Calculations – Key Points

    1. Spectator ions are ions that are not involved in a chemical reaction.

    2. Stoichiometetry of the reaction is the relationship between the amounts of reactants and products involved in a chemical reaction.

    3. Limiting reactant is the reactant that is completely used up in a reaction and determines the amount of products formed.

    4. The concentration of a solution is given by the amount of a solute dissolved in a unit volume of the solution.

    5. Molar concentration is the concentration of a solution expressed in mold/dm^3

    6. The theoretical yield is the calculated amount of products that would be obtained if the reaction is completed.

    7. Actual yield is the amount of pure products that is actually prodcued in the experiment.

    For more key points and exam based questions with full worked solutions please contact Mr Ong @98639833

    #3410

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    Acids and Bases – Key Points

    1. An acid is a substance that produces hydrogen ions, H+, when dissolved in water.

    2. The strength of an acid refers to the extent to which the acid molecules dissociates when dissolved in water.

    3. A base is a substance that reacts with an acid to form a salt and water only.

    4. An alkali is a base that is soluble in water.

    5. Neutralisation reaction is the reaction between an acid and a base to from a salt and water only.

    6. The term concentration tells us how much a substance is dissolved in 1 dm^3

    7. The term strength refers to how an acid or an alkali dissociates when dissolved in water.

    8. The pH scale is a set is a set of numbers used to whether a solution is acidic, neutral or alkaline.

    For more key points and exam based questions with full worked solutions please contact Mr Ong @98639833

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