6.1.2 Wavefronts

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Phase

  1. A phase is the current position in the cycle of something that changes cyclically.
  2. Two vibrating particles are in the same phase if their displacement and direction of motion are the same.
    1. In phase – Same phase
    2. Out of phase – Different phase
    3. Anti-phase – Phase different = 180°

Wavefront

  1. A wavefront is a line or a surface that connects points that are moving at the same phase and has the same distance from the source of the waves.
  2. When a circular wave is formed, a circular wave front is formed.
  3. Characteristics of wavefront:
    1. wavefronts are always perpendicular to the direction of wave propagation. (As shown in the diagram below)
    2. all the points on a wavefront have same distance from the source of the wave.

Wavelength


The wavelength (λ) is defined as the distance between two successive particles which are at the same phase (exactly the same point in their paths and are moving in the same direction.).


 

6.1.1 Understanding Waves

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What is Wave?

  1. A wave is a disturbance or variation that propagates through a medium, often transferring energy.
  2. Waves travel and transfer energy (its amplitude) and information (its frequency) from one point to another, with little or no permanent displacement of the particles of the medium.
Must Know:
Waves transfer energy without transferring physical matter.

 

 

5.5.6 Slide Projector

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Function

Bulb
  1. Bulb with high brightness is used.
  2. The bulb must be placed at the centre of curvature of the concave mirror.
Concave mirror
  1. The function of the concave mirror is to reflect and focus light that shines on it to the direction of the condenser.
  2. This is to increase the brightness of the image.
Condenser
  1. The condenser consists of two Plano-convex lenses.
  2. The function of the condenser is to focus all the light that brightens the whole slide.
  3. It also acts as a heat insulator to stop heat from the bulb so it does not spoil the slide.
Slide
  1. The slide acts as the object.
  2. It is located at a distance between f and 2f from the projector lens so that the image produced is real and magnified.
  3. It is purposely placed upside down so that the image forms on the screen looks upright.
Projector Lens
  1. The projector lens projects the image on the screen that is placed a few meters away.
  2. It can be adjusted to focus a sharp image.
Image The image produced is
  1. real (it form on a screen)
  2. magnified
  3. inverted (Since the slide is placed upside down, hence the image looks upright)

 

5.5.5 Camera

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Functions

Convex lens To focus the light of an object onto the film so that a sharp image can be produced.
Diaphragm To control the size of the aperture and hence control the amount of light move into the camera.
Focusing Ring To adjust the distance between the lens and the film so that the image is sharply focus on the film.
Film
  1. Acts as a screen for the image to form onto it.
  2. Chemical on it will react when exposed to light and produce a photograph.
Shutter Open when picture is taken to allow light move onto the film.
The shutter speed is the length of time when the shutter is open. It control the amount of light move onto the film.
Aperture Open when picture is taken to allow light move onto the film.
The shutter speed is the length of time when the shutter is open. It control the amount of light move onto the film.

Note:

  1. The film, which is normally kept in total darkness, contains a light-sensitive chemical called silver bromide.
  2. When you press the camera button, a shutter in front of the film opens then shuts again, exposing the film to light for a brief moment only. 
  3. Different intensities and colours of light across the image cause varying chemical changes in the film, which can later be developed, 'fixed', and used in printing a photograph.
  4. The image formed on the film is
    1. Real
    2. Inverted
    3. Smaller than the object.

 

5.5.4 Compound Microscope

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Compound Microscope
Object lens Higher power
Eye lens Lower power
Position of the object The object is placed at a position between fo and 2fo.
Nature of the image, I1 Real, inverted and magnified
Position of the image, I1. The first image, I1 must be placed between the optical center of the eye lens with the eye lens principle focus point, fe.
Nature of the image, I2 Virtual, inverted and magnified
Distance in between the two lens The distance between the object lens and the eye lens in a compound microscope is bigger than the sum of the  focal length (fo + fe).
If the distance between both lenses are adjusted to less than (fo + fe), no image can be seen.
Magnification of the compound  microscope.

m1 = Linear magnification of the object lens
m2 = Linear magnification of the object lens

 

5.5.3 Astronomical Telescope

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Astronomical Telescope
Objective lens Lower power
Eye lens Higher power
Position of the object At infinity
Nature of the image, I1 Real, inverted and magnified
Position of the image, I1. At the principle focus of object lens, fo.
Nature of the image, I2 Virtual, inverted and smaller in size.
Distance in between the two lens
  1. The distance between the object lens and the eye lens in a compound microscope is equal to the sum of the  focal length (fo + fe).
  2. If the distance between both lenses are bigger than (fo + fe), no image can be seen.
Magnification of the compound  microscope.

 

 

5.5.2 Magnifying Glass

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  1. Magnifying glass is also known as simple microscope.
  2. A magnifying glass is a single convex lens with short focal length.
  3. The iage formed is
    1. virtual,
    2. magnified
    3. upright
  4. A magnifying glass enlarges the image of an object by increasing the virtual angle at the eye when the object is viewed.

 

5.4.7 Lens Formula

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The Lens Equation

  1. The following is the lens equation that relates the object distance (u), image distance (v) and the focal length.
  2. When using the lens equation to solve problem, it's important to note the positive negative sign of u, v and f.
  3. Table below give the conventional symbol and sign for u, v and f.
Positif
Negatif
u
Real object
Virtual object
v
Real image
Virtual image
f
Convex lens
Concave lens

 

 

5.4.6 Linear Magnification

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The linear magnification is a quantity that indicates the ratio of the height of the image to the height of the object.



m = linear magnification
u = distance of object
v = distance of image
hi = heigth of image
ho = heigth of object