NCTB Class 9-10 Science Chapter 5 “Light for Sight” Solution
Bangladesh Board Class 9-10 Science Solution Chapter 5 Light for Sight Solution Exercises Question and Answer by Experienced Teacher.
NCTB Solution Class 9-10 Chapter 5 “Light for Sight”:
|NCTB Bangladesh Board|
9 – 10 (Nine – Ten Classes)
Light for Sight
Multiple choice questions
(1) What is the least distance of distinct vision of normal eye?
- 5 cm b) 10 cm
- c) 25 cm d) 50 cm
Answer:-a) 5 cm
2) For convex lens,
1) Its power is positive
2) The Middle part of the lens is thin and both the edges are thick.
3) It converges the parallel rays at a point.
Which is correct ?
a) i and ii b) i and ii
c) ii and iii d) i, ii , and iii
Answer:- b) i and iii
- Observe the figure and give the answer of 3 and 4.
3) What is the name of the defect of eye mentioned in the figure.
a) Short – sight b) long – sight
c) presbyopiad) Astigmatism
Answer:- a) short – sight
4) What type of lens should be used to rectify the aforsaid defect?
a) Convex lens
b) concave lens
c) convexo – concave lens
d) plano – concave lens
Que. 1] sejuti cannot see clearly the writing on the blackboard by the teacher from a far distance. On the other hand sejuti’s father faces a problem to see the things nearer. Subsequently, sejuti and her father taken to a doctor. A doctor adviced to use one kind lens to sejuti and a different kind of lens to her father.
A) What is called refraction of light ?
Answer:-In homogeneous mediumlight always travel in a straight line , when a ray of light is incident not perpendicular but obliquely from one transparent medium to another transparent Medium the direction of the ray changes at the surface of separation of the two media. The phenomenon of this change in direction of a ray is called the refraction of light.
B) What does it mean by the least distance of distinct vision ?
Answer:-The minimum possible distance from an eye , at which point an object is seen distinctly, is known as near point of distinct vision and the distance of near point from the eye is known as the least distance of distinct vision.
C) what type of defect the eye attacked sejuti ? Explain .
Answer:-when an eye can see the object near but cannot see the object at a far distance from it, it is called short sight. Sejuti has attacked with the short sight defect of eye . The far point of such an eye stays a bit closer which is less than infinity and the eye can see the object more distinctly when it comes nearer than the least distance of distinct vision.
D) Analyse logically the reason of doctors adviced for the sejuti’s father to use different kind of lens .
Answer:-sejuti has attacked with the short sight defect of eye, and on the other hand her father got attacked with the long sight defect of eye. Thus the doctor advised her father an different kind of lens .
Long sight defect is when an eye can the object at far distance but cannot see the object nearer. Thus to rectify this defect one is to use spectacles of convex lens. Thus the doctor advised him to use different kind of lens than sejuti.
Que.2] see the figure below and answer the question.
A) What is called lens?
Answer:-The transparent refracting medium by two spherical surfaces is known as lens. Mainly lens are of two types- a) convex or converging lens ,
b) concave or diverging lens.
B) What does it mean by power of a lens ?
Answer:-The incident rays parallel to the principal axis of the lens converge at a point on the principal axis after refraction by the convex lens. On the other hand the incident rays to the principal axis of the lens diverge after refraction by a concave lens and it appears to diverge from a point of the principal axis. This capacity of converging and diverging of light rays by a lens is the power of the lens.
C) What is the cause of using the mirror X in fig. -1 ?
Answer:-the hilly roads are usually zigzag. There is often such an invisible turn that the next road is situated at 90° angle. For these reasons it is dangerous to drive in hilly roads, considering these problems there are big size spherical mirrors on the stands kept standing at different turning of hilly roads. As a result, coming nearer to it by looking at a mirror it is seen whether any car is coming from the other side form the turning and accordingly the driver can cautiously control the speed of the car to drive safely.
D) Explain the role of the mirrors P, Q, R, in the car in fig. 2 ?
Answer:-one of the condition of safe driving is to keep an eye all the time on what us happening on all sides of the driver’s car. There are two side view mirrors which is P and R these are used to see the view of both side . And the mirror Q which is on the middle of the inside front of the car i.e rear view mirror this help to see the view of back side of the car.