Karnataka Board Class 8 Science Chapter 17 Our Colourful World
KSEEB Class 8 Science Chapter 17 Textual Questions & Answers
I. Four alternatives are given to each of the following incomplete statements questions. Choose the right answer.
Question 1.
Rearview mirror of motor vehicles contain
(a) plain mirror
(b) convex mirror
(c) concave mirror
(d) convex lens
Answer:
(b) convex mirror
Question 2.
If a ray light is traveling from denser medium to rarer medium and if the angle of incidence is greater than the critical angle, the following takes place.
(a) Total Internal
(b) refraction
(c) dispersion
(d) multiple refractions
Answer:
(a) Total Internal
Question 3.
A concave mirror forms magnified inverted image when the object is placed at
(a) F
(b) C
(c) between F and C
(d) beyond C
Answer:
(c) between F and C
Question 4.
On a new stainless steel spoon if you set the image of your face upside down, then that part of the spoon acts like
(a) convex lens
(b) concave mirror
(c) convex mirror
(d) concave lens
Answer:
(b) concave mirror
Question 5.
You can see the image of your face on the surface of still water. But if the water is disturbed your image will not be clear because of
a) total internal reflection
b) refraction
c) irregular reflection
d) dispersion
Answer:
c) irregular reflection
II. Fill in the blanks with suitable words:
Question 1.
The letter ‘P’ looks like ……….. in a plane mirror.
Answer:
q
Question 2.
The type of lens used by watch repairers is ………..
Answer:
convex lens
Question 3.
Bending of light when it passes from one transparent medium to another is called ……….
Answer:
refraction
Question 4.
Formation of the rainbow is due to …………
Answer:
dispersion of light
III. Answer the following
Question 1.
Give one reason to prove that light is a form of energy.
Answer:
- Plants can carry out photosynthesis with the help of light energy and prepare food. Since light has the ability to do work it is a form of energy.
- One form of energy can be transferred into other forms. Since photocell can change the light into electrical energy. It is a form of energy.
Question 2.
What is the difference between regular and irregular reflection?
Answer:
| Regular reflection |
Irregular reflection |
| 1. happens in a perfectly flat surface or polished surface | 1. happens if the reflecting surface is rough |
| 2. image formed will be clear | 2. image will not be clear |
| 3.pattern of incident light is present in reflecting light | 3. since the light get scattered the pattern of incident light is not found in reflected light |
Question 3.
State the laws of reflection.
Answer:
- Angle of incidence is equal to the angle of reflection.
- The incident ray, the normal drawn to the mirror at the point of incidence and the reflected ray all lie on the same plane
Question 4.
Mention the uses of a concave mirror.
Answer:
Concave mirrors are used by dentists and in the solar furnace and in the headlight of motor vehicles.
Question 5.
Why is the convex mirror used as a rearview mirror in motor vehicles?
Answer:
Convex mirrors always produce erect diminished virtual images of the objects. The driver gets a clear image of the vehicles coming from behind, therefore it is used as a rearview mirror in motor vehicles.
Question 6.
Mention any two effects of refraction of light in daily life.
Answer:
- A coin in a cup that is just invisible can be made visible by pouring water in the cup.
- The bottom of a water tank appears to be raised.
Question 7.
What are the conditions for total internal reflection to take place?
Answer:
The condition for total internal reflection takes place are
- If the light ray travels from a denser medium to a rarer medium.
- Angle of incidence must be greater than the critical angle for the two media.
Question 8.
Draw the diagrams to show the refraction of parallel rays of light in
- convex lens
- concave lens.
Answer:
Question 9.
Mention any four devices that contain a convex lens.
Answer:
The convex lens is used in a simple microscope, compound microscope, telescope, and also in the spectacles used by the people who have hypermetropia.
Question 11.
What is the dispersion of light?
Answer:
The splitting up of white light into its constituent colors is called dispersion.
IV. Match the following :
Answer:
- (e)
- (d)
- (b)
- (c)
KSEEB Class 8 Science Chapter 17 Additional Questions & Answers
Question 1.
What is light?
Answer:
Light is a form of energy enable us to see the things
Question 2.
Mention the sources of light.
Answer:
Major source of light is the sun. Light can also be produced with the help of candles bulbs. Fluorescent lamps, gas lamps etc.
Question 3.
Write an experiment to prove the laws of reflection.
Answer:
Keep a white sheet of paper on one side of the hollow box and pin it at the four corners. Make incisions on the box to the size of the cardboard slit and mirror and the cardboard slit perpendicularly in the incisions made, pass light from a torch through the opening of the cardboard slit, in an oblique manners.
We can see light ray getting reflected after striking the mirror. Mow carefully draw lines with the help of pencil to mark the position of the mirror the incident ray and the reflected ray on the paper remove the mirror comb and torch. Draw perpendicular line to the mirror at a point where the incident ray strikes the mirror.
Which is called as normal measure the angle of incidence and angle of reflection. We can find that angle of incidence is equal to the angle of reflection. The incident ray, normal and reflected ray all lie on the same plane.
Question 4.
Mention the characteristic of the image formed by a plane mirror.
Answer:
- The image is laterally inverted.
- It is virtual.
- The image on the plane mirror is erect.
- The image is as far behind the mirror as the object in front of it.
Question 5.
What is meant by lateral inversion?
Answer:
Lateral inversion means lift of the object will become right of the image and right of the object will become left of the object.
Question 6.
Draw a ray diagram to show the laws of reflection by a plane mirror.
Answer:
Keep a white sheet of paper on one side of the hollow box and pin it at the four corners. Make incisions on the box to the size of the cardboard slit and mirror and the cardboard slit perpendicularly in the incisions made, pass light from a torch through the opening of the cardboard slit, in an oblique manners.
We can see light ray getting reflected after striking the mirror. Mow carefully draw lines with the help of pencil to mark the position of the mirror the incident ray and the reflected ray on the paper remove the mirror comb and torch. Draw perpendicular line to the mirror at a point where the incident ray strikes the mirror.
Which is called as normal measure the angle of incidence and angle of reflection. We can find that angle of incidence is equal to the angle of reflection. The incident ray, normal and reflected ray all lie on the same plane.
Question 7.
What are spherical mirror and mention the types?
Answer:
Spherical mirror is a part of a sphere with polished surface on one of the side.
The two types of spherical mirror are
- concave mirror
- convex mirror.
Question 8.
Draw diagrams to show the reflection of parallel rays of light in
1. Concave mirror
2. convex mirror.
Answer:
Question 9.
What is meant by the following terms?
- Pole of the mirror
- principal focus
- focal length
- center of curvature
- radius of cunaiure
- principal axis
- Object distance
- image distance.
Answer:
- Pole of the mirror : pole of the mirror is the center of the reflecting surface. The ray of light along the principal axis which is incident on the pole of the mirror retraces its path along the principal axis.
- Principal focus : It is the point of convergence of a parallels beam of light which are also parallel to principal after reflection. It is denoted by ‘F’.
- Focal length : The distance between the pole of the mirror and the point of focus reflected parallel rays of light which are incident on the mirror is called focal length. It is denoted by ‘P’.
- Center of curvature : It is center of the sphere of which the mirror is a part. It is denoted by ‘C’.
- Radius of curvature : The radius of the sphere of which the mirror apart is called radius of curvature it is denoted by ‘V’. the radius of curvature is twice the focal length r = 2 ‘f’
- Principal axis : The imaginary extended line on which the pole of the mirror, the point of focus and the center of the curvature are located is called principle axis.
- Object distance : The distance of the object from the pole of the mirror is called object distance it is denoted by ‘V’.
- Image distance : The distance between the mirror and the image is called image distance it is denoted by ‘V’.
Question 10.
Write the equation to show the relation among focal length object length and image length.
Answer:
\(\begin{array}{l}{\text { Focal length }=\frac{\text { Product of image distance }}{\text { Sum of image distance }}} \\ {=\frac{\text { and object distance }}{\text { and object distance }}}\end{array}\)
Question 11.
What is refraction?
Answer:
The bending of light when it passes from one transparent medium to another is called refraction.
Question 12.
What happens when a ray of light passes from one transparent medium to another transparent medium?
Answer:
Water is a denser medium than air when an oblique ray of light travels from rarer medium to denser medium it bends towards the normal that means angle of incidence will be greater than angle of reflection.
Question 13.
What is total internal reflection?
Answer:
The phenomenon of reflection of light when a ray of light traveling in a denser medium gets incident at the interface of two media at an angle greater than critical angle is called total internal reflection.
Question 14.
Write the application of total internal reflection.
Answer:
The applications of total internal reflection are.
- To explain the sparking nature of diamond.
- To explain the formation of mirages
- It is used in optic fiber cable
- It is used in endoscopy.
Question 15.
What do you mean by endoscopy?
Answer:
Endoscopy is an instrument by which doctors can really see the inside of the stomach. This in statement works using the principle of total internal reflection.
Question 16.
Define mirage? How is it formed.
Answer:
Mirage is an optical illusion created by total internal reflection of light Under normal circumstances the density of air is uniform on tar roads and hence light travels in straight line. The air layer in contact with earth gets heated up and becomes rare when compared to the upper strata of atmosphere.
Light coming from the distant objects is total internally reflected. This creates an illusion of reflection in water. The inverted image caused due to the hot air volume below is responsible for this. This phenomenon is rare in case of positions above the level of the observer.
Question 17.
What is a lens? Name the types of lens.
Answer:
Any curved piece of transparent medium is called a lens.
The two types of lens are
- convex lens
- concave lens.
Question 18.
What is Spectrum?
Answer:
A band of seven colors (VIBGYOR) formed by splitting of white light is called a spectrum.
Question 19.
Draw a neat diagram to show the refraction of light in a prism.
Answer:
Question 20.
The bottom of a water tank appears to be raised.
Answer:
The bottom of the water tank appears to be raised because the light gets refracted when it enters a different medium.
Question 21.
A pencil partially immersed in an oblique manner in water appears to be bent.
Answer:
A pencil partially immersed in an oblique manner in water appears to be bent due to the refraction of light.
Question 22.
Stars appear to twinkling.
Answer:
Stars appear to be twinkling as the beams of light deviate from their path due to refraction.
Question 23.
In the rainbow, we may not see all the seven colors.
Answer:
In the rainbow, we may not see all the seven colors due to the overlapping of colors.
Question 24.
Diamond sparkles.
Answer:
Diamond sparkles due to the effect of total internal reflection.