O Level – Physics

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  • #2903

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    Waves – Key Concepts

    1. Periodic motion is motion that repeats at regular intervals.

    2. One complete periodic motion – from one extreme position to the other extreme position and back – is known as an oscillation or a vibration

    3. Waves transfer energy from one point to another without any part of the medium being transferred.

    4. There are two types of wave motion: transverse and longitudinal
    When the direction of vibrations is perpendicular to the direction in which the wave moves, the wave is a transverse wave. For example: water waves, light waves.

    5. When the direction of vibrations is parallel to the direction in which the wave moves, the wave is longitudinal. For example: sound waves, pushing and pulling of a Slinky®

    6. Crests and troughs: These are the high points and low points that characterise transverse waves only. For longitudinal waves, the terms compressions and rarefactions are used.

    7. Amplitude (A): The amplitude of one oscillation is the amplitude of the wave. It is half the vertical distance between a wave crest and a wave trough. Its SI unit is the metre (m).

    8. Wavelength (λ): This is the shortest distance between any two points (such as two successive crests or troughs) on a wave that are in phase. Its SI unit is the metre (m).

    9. Period (T): the period of one oscillation is the period of one wave. It is the time taken for a wave crest to move through a distance equal to its wavelength.

    10. Frequency (ƒ): This is the number of complete waves produced per second. Its SI unit is the Hertz (Hz). Frequency and period is related by the equation: ƒ=1∕T

    11. Wave speed (v): This is the distance travelled by a wave in one second. Its SI unit is metres per second (m s-1). The speed of a wave can be computed by the equation: v = ƒλ

    12.Wavefront: A wavefront is an imaginary line on a wave that joins all points which are in the same phase of vibration.

    From O Level Physics Tutor

    #2957

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    Electromagnetic Waves

    Some useful applications of electromagnetic waves include:

    (a) Gamma-rays in radiation therapy (or cancer treatment)
    (b) X-rays in medical (X-ray images) and everyday applications (X-ray scanners)
    (c) Ultraviolet radiation in sunbeds and sterilisation of medical equipment
    (d) Visible light in optical fibres for medical uses and telecommunications
    (e) Infrared radiation in remote controllers and intruder alarms
    (f) Microwaves in microwave ovens and satellite television
    (g) Radio waves in radio and television communications

    From O Level Physics Tutor

    #2972

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    Electromagnetic Waves – Key Concepts

    1. Some useful applications of electromagnetic waves include:

    (a) Gramma-rays in radiation therapy (or cancer treatment)
    (b) X-rays in medical (X-ray images) and everyday applications (X-ray scanners)
    (c) Ultraviolet radiation in sunbeds and sterilisation of medical equipment
    (d) Visible light in optical fibres for medical uses and telecommunications
    (e) Infrared radiation in remote controllers and intruder alarms
    (f) Microwaves in microwave ovens and satellite television
    (g) Radio waves in radio and television communications

    2. Some effects of absorption of electromagnetic waves by humans include:

    (a) Infrared heating
    (b) Damage to different tissues and organs of the human body due to ionising radiation

    From O level Physics Tutor

    #2986

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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

    #2998

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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

    #3042

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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

    #3066

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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

    #3095

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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

    #3111

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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

    #3139

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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

    #3157

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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

    #3214

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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

    #3236

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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

    #3266

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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

    #3318

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    Key Points – Mass, Weight and Density

    1. Inertia depends only on the mass of the object. Even if temperature or density of the object changes, as long as the mass remains constant, its inertia remains constant.

    2. When ice melts, its density increases. Mass remains constant since the number of molecules remains the same.

    Density = Mass/Volume

    Therefore volume decreases

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

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