Telangana SCERT Class 10 Physical Science Chapter 4 Solution – Refraction of Light at Curved Surfaces. Here in this post we provides Class 10 Physical Science Refraction of Light at Curved Surfaces Telangana State Board Solution. Telangana State Board English Class X Medium Students can download this Solution to Solve out Improve Your Learning Questions and Answers.
Telangana State Board Class 10 Physical Science Chapter 4 Refraction of Light at Curved Surfaces Solution:
CHAPTER: – 4
Refraction of Light at Curved Surfaces
Exercise: –
Reflections on concepts
1) How do you verify experimentally that the focal length of a convex lens is increased when it is kept in water?
Ans: – If we dipped a black stone in a cylindrical shape fill with water and after that if we see by the lense then we will see that at a certain distance it is seen from lense. After when we increasing the height from the previous point, we will see that itsfocal length is not same as previous one from there we can conclude that the focal length of any convex lense in increased when it kept in water.
2)How do you find the focal length of a lens experimentally?
Ans: – If we place a candle at a certain distance say 30cm from theconvex lens and kept a screen at a distance along with the principal axis. Then by changing the distance of the object we take 3 to 4 values of image then we will find the value of focal length of the lens.
3) Draw ray diagrams for the following positions and explain the nature and position of image.
- Object is placed at C2
- Object is placed between F2 and optic centre P.
Application of concepts
1)Two converging lenses are to be placed in the path of parallel rays so that that rays remain parallel after passing through both lenses. How should the lensesbe arranged? Explain with a neat ray diagram.
Ans: –
2)The focal length of a converging lens is 20cm. An object of 2cm height is at a distance of 60cm from the lens. Where will the image be formed and what kind of image is it? And also find the height of the image (AS1)
Ans: –As we all know that, 1/f = 1/v – 1/u.
Here, f=20cm, u=-60cm and v=?.
So, 1/v= 1/f – 1/u ;
Or, 1/v = 1/20 + 1/60;
Or, v= 30cm.
And magnification m=v/u = hi/ho,
Here, ho=2cm.
So, 30/60=hi/2;
Or, hi= 1cm.
3) A double convex lens has two surfaces of equal radii ‘R’ and refractive indexn = 1.5, find the focal length ‘f’.
Ans: – As we all know, 1/f = (u-1)(1/R1 – 1/R2);
Here, u= 1.5, R1=R and R2=-R.
So, 1/f= (1.5 – 1)(1/R + 1/R);
Or, 1/f= 0.5×2/R;
Or, f=R.
4) Find the refractive index of the glass which is a symmetrical convergent lens if its focal length is equal to the radius of curvature of its surface.
Ans: – As , 1/f=(u-1)(1/R1 – 1/R2);
Let the radius of curvature is R.
Here, f=R, and R1=R, R2=-R. u= refractive index,
So, 1/R= (u-1)(1/R + 1/R);
or, (u-1)/2= 1;
or, u=1.5.
Higher Order Thinking Questions
1) A convex lens is made up of three different materials as shown in the fig-Q(1). How many of images does it form?
Ans: – As in this image there are three different types of colours and we know each colour has different refractive index so there will be three different images will form.
2) You have a lens. Suggest an experiment to find out the focal length of thelens.
Ans: – For finding the focal length of a lens we have to place the light source as candle, a screen where it shadow is fallen along with principal axis of lens and see the image of candle by changing the object distance and we will see different position of image in screen and we will see that. After getting different values we can calculate the focal length.
3) Fig.-Q(3) shows ray AB that has passed through a divergent lens. Construct the path of the ray up to the lens if the position of its foci is known.
4) FIG – Q(4) shows a point light source and its image produced by a lens with an optical axis N1N2. Find the position of the lens and its foci using a ray diagram.
Ans: – From the diagram we can clearly see that the lens must be placed in between the focus and pole in that diagram.
5) Find the focus by drawing a ray diagram using the position of source S and the image S/given in the fig.-Q(5).
Ans: –
6) A parallel beam of rays is incident on a convergent lens with a focal length of 40cm. Where a divergent lens with a focal length of 15 cm should be placed for the beam of rays to remain parallel after passing through the two lenses? Draw a ray diagram.
Ans: –
7) Suppose you are inside the water in a swimming pool near an edge. A friend is standing on the edge. Do you find your friend taller or shorter than his usual height? Why?
Ans: – The height of any object is seen in different from the different medium as all have individual refractive index. The refractive index of water is different from the air and for that reason we see that a friend is standing on the edge of the swimming pool is taller as comparing to his actual height. As the light when passes from the rarer to denser medium its height is increased.
MULTIPLE CHOICE QUESTIONS
1) Which one of the following materials cannot be used to make a lens?
a) water b) glass c) acrylic d) clay.
Ans: – option (d) Clay.
2) Which of the following is true?
a) the distance of virtual image is always greater than the object distance for convex lens
b) the distance of virtual image is not greater than the object distance for convex lens
c) convex lens always forms a real image
d) convex lens always forms a virtual image.
Ans: – option (b).
3) Focal length of the Plano-convex lens is …………. when its radius of curvature of the surface is R and n is the refractive index of the lens.
a) f = R b) f = R/2 c) f = R/(n–1) d) f = (n–1)/R.
Ans: – option (a) f=R.
Additional Questions
Question 1: Define center of curvature, pole and principal axis of a curved mirror?
Answer 1: Center of curvature: The center of the sphere, of which the curved surface is a part, is called the center of curvature. It is denoted by the letter ‘C’.
Pole: center of center of curvature is called a pole of curved mirror.
Principal axis: axis which passes from pole and center of curvature is called principal axis.
Question 2: when a ray of light travels from denser medium to rarer medium then?
- a) It will bend towards normal.
- b) It will bend away from the normal.
- c) It will move without bending.
- d) None of these.
Answer 2: B. It will bend away from the normal.
When a ray of light travels from denser medium to rarer medium it bends away from the normal, by Snell’s law.
Question 3: When a ray of light travels from denser medium to rarer medium in a curved surface and it passes through or appears to pass through the center of curvature, then it will bend or not , and why?
Answer 3: When a ray of light travels from denser medium to rarer medium in a curved surface and it passes through or appears to pass through the center of curvature, in this case incident angle is zero so reflected angle will refracted angle will also zero, by Snell’s law.
So light rays pass through without bending.
Question 4: What is the correct relation between object and image distance for curved surface , when refractive index of object side medium is and refractive index of object side medium is . where R is radius of the curve surface.
Question 5: A coin is placed inside a water tank, then for a person who is able to see the coin, the coin will be at?
a) At actual distance.
b) At far more depth than actual depth.
c) At less depth than actual depth.
d) Data is insufficient.
Answer 5: C: At less distance than actual distance.
When a light rays travel from denser medium to rarer medium, it bends away from the normal, and for a person it seems to appear that light rays are coming from apparent height, so he feels coin depth is less than actual depth.
Question 6: What is a lens?
Answer 6: A lens is formed when a transparent material is bounded by two surfaces of which one (or) both surfaces are spherical. That is a lens is bounded by at least one curved surface.
Question 7: What are the different types of lens?
Answer 7: Lenses can be of various types.
1) Biconvex.
2) Plano-convex.
3) Concavo-convex.
4) Biconcave.
5) Plano-concave.
6) Convexo-concave.
Question 8: Define optical center of lens (P) and focal length of lens?
Answer 8: every lens has two centers of curvature. The line joining to this center of curvature is called the principal axis and the midpoint to these two centers of curvature is called the optical center of the lens.
Focal length: The distance between optical center and focal point is called the focal length for the lens.
Question 9: In solar cookers and car headlights, which type of mirror is used?
Answer 9: In solar cookers and car headlights, concave mirrors are used.
Because in a concave mirror all parallel rays pass through a fixed point called focal point.
Question 10: What is meant by magnification in curved lenses?
Answer 10: Magnification means what is the size of image as compared to object size or in general. The increase in image size formed by spherical mirrors in comparison to the size of the object is called magnification.
Question 11: When an object of height 2m is placed at the center of curvature then what will be the magnification and height of the image?
Solution 11: When an object is placed at the center of curvature, its image also forms at the center of curvature.
So magnification
So, m = + 1 and
Height of image = 2m
Question 12: when an object is placed at between infinite and center of curvature where will the image be formed by a convex lens?
Answer 12: When an object is placed at between infinite and center of curvature the image will be formed at between focal point and center of curvature by a convex lens.
Question 13: Magnification of concave lens?
a) Always positive
b) Always negative
c) It can be positive or negative
d) Zero
Answer 13: a) Always positive.
Image formed by concave lens is always virtual and erect and diminished image and it does not depend on the position of the object position, so m should be always positive.
Question 14: when a convex lens is immersed in water its focal length and nature will be changed or not, if yes what will be the effect?
Answer 14: When a convex lens is immersed in water then reflective index of medium will be increase so by lens maker formula will decrease , so f will increase and f will become negative that means it will diverse all rays , so it will behave as a concave lens.
Question 15: Write lens maker formula, and what will be the effect in focal length when wavelength of incident source is increased?
When we use a higher wavelength than the refractive index of the lens will decrease means the focal length of lens increases.
Question 16: What is the focal plane?
Answer 16: When all rays of light which are parallel to each other but not parallel to the principal axis, meet at a plane, which passes through the focal point also perpendicular to the principal axis, is called focal plane.
Question 17: When an object is placed at an infinite distance from pole then what size and image position of object?
Answer 17: When an object is placed at an infinite distance from pole image will be formed at focal point and size of image will be point size.
Question 18: Compare real and virtual images formed by lens?
Answer 18:
1) Real images are always formed on the opposite side of an object but virtual images will be on the same side of the object.
2) Real image will be always inverted and virtual image will be erect with respect to object.
3) Real images can be found on screen, but virtual images cannot be found on screen.
4) In Real image rays will converge and they will meet at one point, but in virtual image rays will diverge and they will feel to meet at a point.
Question 19: Difference between convex and concave lens?
Answer 19:
1) Convex lens thicker at center and thinner at corners but concave lens thinner at center and thicker at corners.
2) Convex lenses can make both real and virtual images but concave lenses always make virtual images.
3) Convex lens used to correct Hypermetropia and concave lens used to correct myopia.
4) Convex lenses converge rays but concave lenses diverge rays.
Question 20: Draw a ray diagram due to a convex lens when an object is placed?
1) Object is at infinite
2) Object is at center of curvature
3) Object is between infinity and center of curvature
Answer 20:
1) Object is at infinite:
2) Object is at center of curvature:
3) Object is between infinity and center of curvature:
Question 21: A convex lens made by two different materials is shown in figure. How many images will form by this convex lens?
Answer 21: Here the upper and lower part both have different reflective index so both will have different focal length , so both sides will draw an image at different different positions.
So the total number of images will be two.
Question 22: A ray passes through the center of the pole , then ?
1) It will deviate away from the principal axis
2) It will deviate towards the principal axis
3) It will travel without deviation
4) None of above
Answer 22: C. A ray passes through the center of the pole , It will travel without deviation.
Question 23: What are symbols used for convex and concave lenses?
Answer 23:
For Convex lens
For Concave lens
Question 24: A convex lens of focal length 20 cm is placed at a distance of 24 cm from the wall, at what distance image should be placed so that image will form at the wall ?
Answer 24:
Here v = +24 cm
f = + 20 cm
u =?
So by lens formula
Question 25: If a plano convex lens for that radius of curvature is 20 cm and focal length is 60 cm then what will be its focal length?
Answer 25:
Question 26: A biconvex lens of radius of curvature R , having refractive index “n” , then what will be the
1) Focal length.
2) Image distance (when image is kept at center of curvature).
Answer 26:
1) Focal length :
By lens maker formula :
2) Image distance :
By lens formula :
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