Science [2 Mark Questions]

1. 
   
2. magnified, real and inverted.

Light rays get deviated from their original path while entering from one transparent medium to another medium of different optical density. This deviation (change in direction) in the path of light is due to the change in velocity of light in the different medium. The velocity of light depends on the nature of the medium in which it travels.

• • • (i) Convex
      (ii) Concave.

• • • Mirage
    • Twinkling of stars

• • • Spectacular brilliance of diamonds.
    • Transmission of audio and video signals to long-distance through optical fibres

• • • Optical fibres are extensively used for transmitting audio and video signals through long distances.
    • Optical fibres too make use of the phenomenon of total internal reflection.
    • Optical fibers are fabricated with high-quality composite glass/quartz fibres.
      Each fibres consists of a core and cladding. The refractive index of the material of the core is higher than that of the cladding.

    When a signal in the form of light is directed at one end of the fibre at a suitable angle, it undergoes repeated total internal reflection along the length of the fibre and finally comes out at the other end. Optical fibres are extensively used for transmitting and receiving electrical signals which are converted to light between the ends of the fibre, over long distances.

• • Refraction of light:

    • Light from a star is refracted as it passes through our atmosphere because the light
      passes rapidly through moving cells of air with different densities, temperatures, etc.
    • These cells bend light by different amounts and make the apparent position of the star move around. This movement is seen as twinkling.

• • Mirage is an optical illusion caused by the refraction of light from the sky by heated air.
  • The air near the ground becomes hotter than the air at higher levels.
  • The refractive index of air increases with its density. Hotter air is less dense, and has smaller refractive index than cooler air.
  • If the air currents are small, that is, the air is still, the optical density of different layers of air increases with height.
  • As a result, light from an object such as a car passes through a medium whose refractive index decreases towards the ground.
  • Thus, a ray of light from such an object successively bends away from the normal and undergoes total internal reflection, if the angle of incidence for the air near the ground exceeds the critical angle.

• • Light must travel from denser medium (Water) to rarer medium (Air).
  • The angle of incidence inside the denser medium must be greater than that of the critical angle.

• The image formed behind the mirror
• Enlarged
• Virtual
• Erect

• Always formed behind the mirror between P & F.
• Virtual & erect
• Size is always smaller than the object.
• Magnification is always positive.

• It always forms virtual, erect, and diminished images.
• The field of view increases.
•  

• The pencil dipped in water appears bent due to the refraction of light.
  The angle of refraction depends on the refractive index of the medium.

• Image Position: At C, itself
  Size: Same size
  Nature : (i) Real
  (ii) Inverted

• The image is formed behind the mirror between the pole (P) and focus (F).
• Virtual and erect image.
• Diminished image.

• As a shaving mirror: Magnified face will be seen
• As a dentist head mirror: Focuses the lights on to see a small area of the body (teeth, throat, etc.)
• As reflectors: To get a powerful beam of light
• In solar heaters: To focus sun light for heaters

• Concave mirrors are used as reflectors in torches, vehicle headlights and searchlights.
• To get a powerful parallel beam of light.

• • The radius of the hollow sphere of which the spherical mirror forms a part is called the radius of curvature (R)
    R = 2 × focal length

• • If the reflecting surface is curved inwards that is called concave mirror.
  • The reflecting surface is curved outwards, then it is called convex mirror.

• • It is always virtual and erect.
  • Its size is equal to that of the object
  • It is formed at the same distance behind the mirror as the object is in front of the mirror.
  • It is laterally inverted.
  •  

• • The incident ray, the normal at the point of incidence and the reflected ray, all lie in the same plane.
  • Angle of incidence is equal to the angle of reflection.
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