Physics Form 4 Notes

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  • Theme 3 -The Nature of Waves

    Mr. N. Briffa B.Ed (Hons.)

    1

    Waves carry _______________ from one place to another. There are two kinds of waves:

    a) Transverse waves b) Longitudinal waves.

    Transverse waves are made up of _________________ and ____________________. Definition of a transverse wave: It is a wave in which the vibrations are _________________________ (900) to the direction of the wave.

    Examples of transverse waves: ____________________, _________________, __________________.

    Longitudinal waves are made up of ______________________ and ________________________. Definition of a longitudinal wave: It is a wave in which the vibrations are ________________________ (1800) to the direction of the wave.

    Example of longitudinal wave: ______________________. http://www.youtube.com/watch_popup?v=Rbuhdo0AZDU

  • Theme 3 -The Nature of Waves

    Mr. N. Briffa B.Ed (Hons.)

    2

    ( ) S.I. unit: metre (m) The wavelength of a wave is the length of a single wave. It is denoted by the Greek letter (read as lambda). a) Transverse waves The wavelength ( ) for a transverse wave is the length of a single wave made up of a crest and a trough. However, it is also equal to the distance between two successive ______________ or two successive ___________________.

    b) Longitudinal waves The wavelength ( ) for a longitudinal wave is the length of a single wave made up of a compression and a rarefaction. However, it is also equal to the distance between two successive ______________________ or two successive ___________________.

    http://einstein.byu.edu/~masong/HTMstuff/WaveTrans.html

    S.I. unit: metre (m)The displacement is the height of the wave, from its rest position. The maximum displacement is called __________________. So the amplitude is the height of a crest or the depth of a trough. The greater the amplitude, the greater the ________________ of the wave.

    At which points is the displacement zero metres? _____________________________________ At which points do we measure the amplitude? _____________________________________

    3 dimensional view

  • Theme 3 -The Nature of Waves

    Mr. N. Briffa B.Ed (Hons.)

    3

    S.I. unit: Hertz (Hz)

    Definition: It is the number of waves in _________ second. If 5 waves are generated in one second, then the frequency = ___________.

    If 100 waves are generated in one second, then the frequency = __________.

    The frequency of a wave can only change if the frequency of the source changes. If you dip your finger in water 3 times in 1 second, your frequency (the source) is 3Hz and the frequency of the waves is also 3Hz as 3 waves are produced every second. If the waves move in deep or shallow water the frequency will still be 3Hz as you would still be producing 3 waves in one second. Unless you change your frequency (source), the frequency of the waves will not change.

    S.I. unit: seconds (s)

    Definition: It is the time taken to complete one wave. If it takes 3 seconds to complete one wave, then the periodic time = ___________.

    If it takes 0.2 seconds to complete one wave, then the periodic time = __________.

    f = 1 and T = 1 T f Example:

    If 5 waves are produced in one second, find: a) the frequency, b) the periodic time.

    _______________________________________________________________________________________

    _______________________________________________________________________________________

  • Theme 3 -The Nature of Waves

    Mr. N. Briffa B.Ed (Hons.)

    4 Frequency (f) =

    no of waves in 1 second Periodic Time (T) = Time for one complete wave

    Ex 1

    Ex 2

    Ex 3

    Ex 4

    Ex 5

    Ex 6

    Ex 7

    Find the:

    a) Periodic time _________________________________ b) Frequency __________________________________

    Ex 8

    Six waves hit a breakwater every minute. Find the: a) frequency ____________________________________________________________________ b) periodic time ____________________________________________________________________

  • Theme 3 -The Nature of Waves

    Mr. N. Briffa B.Ed (Hons.)

    5

    Ex 9

    The pendulum takes 2 seconds to swing from A to B. If the horizontal distance from A to B is 1m, find:

    a) its amplitude of vibration _______________________________

    b) its periodic time _______________________________________

    c) its frequency __________________________________________

    Ex 10

    During an earthquake, the upper part of a skyscraper moves from side to side, a horizontal distance of 4m in 1.2 seconds. Find:

    a) its amplitude of vibration _______________________________

    b) its periodic time _______________________________________

    c) its frequency __________________________________________

    Ex 11

    The ruler is placed at the edge of a table and is set to vibrate as shown. If the end of the ruler moves a vertical distance of 3cm in 0.2 seconds, find:

    a) its amplitude of vibration _______________________________

    b) its periodic time _______________________________________

    c) its frequency __________________________________________

    !S.I. unit: metres per second (m/s) This is the velocity with which the wave travels.

    Velocity = Frequency x Wavelength v = f (m/s) (Hz) (m) Example 1:

    Find the velocity of a wave having a frequency of 3Hz and a wavelength of 0.4m. ______________________________________________________________________________________________________________________________________________________________________________ Example 2:

    Find the frequency of a wave which is moving at 2m/s and which has a wavelength of 30cm. ______________________________________________________________________________________________________________________________________________________________________________

  • Theme 3 -The Nature of Waves

    Mr. N. Briffa B.Ed (Hons.)

    6

    "#

    Gamma rays have the ____________________ frequency, the _____________________ energy and the

    __________________________ wavelength.

    Radio waves have the _____________________ frequency, the _______________________ energy and

    the __________________________ wavelength.

    Gamma rays, X-rays, Ultraviolet, Visible light, Infra-red, Microwaves and Radio waves are all

    electromagnetic waves that make up the _____________________________________________. Except for

    visible light, all the other waves are invisible to the human eye.

    Common properties of Electromagnetic waves:

    1. They are all __________________________ waves.

    2. They do not need a medium to travel through, so they can travel in a ________________________.

    3. They have a common ___________________ (3 x 108 m/s or 300,000,000 m/s).

    4. Being waves they all carry __________________.

    5. They obey the laws of reflection, refraction and diffraction.

    6. They are uncharged. (not + or - )

  • Theme 3 -The Nature of Waves

    Mr. N. Briffa B.Ed (Hons.)

    7

    Approximate (m)

    Source Use Additional information

    Gamma

    Is very penetrating and can be very dangerous if used inappropriately. Can be detected with a Geiger-Muller tube.

    X-rays

    Produced when electrons hit a metal target. Can penetrate flesh but not bones and so produces a shadow, making fractures visible. Parts of the body need to be covered with lead. Can be detected by photographic plates.

    Ultraviolet

    Can be detected by using fluorescent chemicals making objects glow in the dark.

    Visible light

    The only radiation which we can see. Can be further divided into seven colours.

    Infra-red

    They can be detected by using a thermometer with a blackened bulb.

    Microwaves

    Microwaves make the water particles contained in food vibrate causing heating. They cause burns if absorbed by the body.

    Radio waves

    Information is encoded into a radio wave, transmitted to a receiver where it is decoded.

  • Theme 3 -The Nature of Waves

    Mr. N. Briffa B.Ed (Hons.)

    8

    $%

    Water waves are transverse waves. They can be studied in a __________________________. Architects and engineers use ripple tanks to study the best design for breakwaters before they start projects on a large scale. How do you produce straight waves in a ripple tank? By using a _____________________ that is forced to move up and down by an electric motor. How do you produce circular waves in a ripple tank? By using a _____________________ that is forced to move up and down by an electric motor. A _____________________ is an instrument that makes waves appear stationary. The ___________________ is equal to the distance between two successive wavefronts and is measured with a metre ruler.

    $

    The angle of incidence (i) is equal to the angle of reflection (r). Draw the normal and the reflected wavefronts in each diagram.

    Underline the correct answer:

    After the waves are reflected: a) the wavelength ( increases, remains the same, decreases) b) the frequen