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CLASS - 10 SCIENCE IMPORTANT QUESTIONS OF MARK 3  FOR BOARD EXAMINATION

QUESTION NO. 50

Define the term power of accommodation. Write the modification in the curvature of the eye lens which enables us to see the nearby object clearly.

ANSWER NO. 59

POWER OF ACCOMMODATION

The ability of eye lens to adjust it's focal lenght is called accommodation. 
     The eye lens lens is composed of a fibrous, jelly - like material. It's curvature be modified to some extent by the ciliary muscles. When we look at objects closer to the eye, the ciliary muscles contract. This increases the curvature of the eye lens. The eye lens then becomes thicker. The focal length of the eye lens decreases. This enable us to see nearby object clearly.

QUESTION NO. 51


When do we consider a student sitting in the class to be myopic ? List two causes of this defect. Explain using a ray diagram how this defect of eye can be corrected.

ANSWER NO. 51


In myopic condition student will not be able to see the written words on the blackboard clearly from the last bench.

 CAUSES


This defect may be arise due to 
(i) Excessive curvature of the eye lens
(ii) Elongation of the eyeball.
    This defect can be corrected by using a concave lens of suitable power.

QUESTION NO. 52


What is scattering of light ? Use this phenomenon to explain why.
(i) the sun appears reddish at sunrise

ANSWER NO. 52


SCATTERING OF LIGHT

Scattering occurs when light pass through an imperfect medium and are deflected from a straight path.


(i) In the morning, the sun is at the horizon sunlight has to travel a long distance through thick layers of air. The colloidal particles in the sky like molecules of air scatter away colours of shorter wavelength like blue. So colours of longer wavelength enter our eye like red. Hence the sun appears reddish during morning.

QUESTION NO. 53


What is rainbow ? Draw a labelled diagram to show the formation of a rainbow.

ANSWER NO. 53


rainbow is an arch of colours visible in the sky, caused by the refracted and dispersion of the sun's light by rain or other water droplets in the atmosphere.

QUESTION NO. 54

Draw magnetic field lines around a bar magnet. List the properties of magnetic field lines. Why two field lines are not crossed each other.

ANSWER NO. 54

PROPERTIES OF MAGNETIC FIELD LINES


  1. They do not intersect each other.
  2. The force of attraction is strongest near the pole due to more numbers of magnetic field line per unit area at poles.
  3. Emerging from the north pole of the magnet to its south pole.
   Two magnetic field lines do not intersect each other because if it happens it means at the point of intersect the the compass needle will show two different direction which is not possible.








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