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NCERT Solutions for Class 10 Maths Chapter 8 Introduction to Trigonometry Ex 8.4 are part of NCERT Solutions for Class 10 Maths. Here we have given NCERT Solutions for Class 10 Maths Chapter 8 Introduction to Trigonometry Ex 8.4.

Board	CBSE
Textbook	NCERT
Class	Class 10
Subject	Maths
Chapter	Chapter 8
Chapter Name	Introduction to Trigonometry
Exercise	Ex 8.4
Number of Questions Solved	5
Category	NCERT Solutions

NCERT Solutions for Class 10 Maths Chapter 8 Introduction to Trigonometry Ex 8.4

Question 1.
Express the trigonometric ratios sin A, sec A and tan A in terms of cot A.
Solution:
From trigonometric identity, cosec² A – cot² A = 1, we get

Question 2.
Write all the other trigonometric ratios of ∠A in terms of sec A.
Solution:
Since sin² A + cos² A = 1, therefore

Question 3.
Evaluate:
(i)

(ii) sin 25° cos 65° + cos 25° sin 65°
Solution:

(ii) sin 25° cos 65° + cos 25° sin 65° = sin 25° cos (90° – 25°) + cos 25° sin (90° – 25°)
= sin 25° sin 25° + cos 25° cos 25°
= sin² 25° + cos² 25° = 1

Question 4.
Choose the correct option. Justify your choice.
(i) 9 sec² A – 9 tan² A =
(A) 1
(B) 9
(C) 8
(D) 0

(ii) (1 + tan θ + sec θ) (1 + cot θ – cosec θ ) =
(A) 0
(B) 1
(C) 2
(D) -1

(iii) (sec A + tan A) (1 – sin A) =
(A) sec A
(B) sin A
(C) cosec A
(D) cos A

(iv) \(\frac{1+\tan ^{2} A}{1+\cot ^{2} A}\)
(A) sec² A
(B) -1
(C) cot² A
(D) tan² A
Solution:
(i) 9 sec² A – 9 tan² A = 9(sec² A – tan² A) = 9 x 1 = 9
Correct option is (B)

Question 5.
Prove the following identities, where the angles involved are acute angles for which the expressions are defined.

Solution:

We hope the NCERT Solutions for Class 10 Maths Chapter 8 Introduction to Trigonometry Ex 8.4, help you. If you have any query regarding NCERT Solutions for Class 10 Maths Chapter 8 Introduction to Trigonometry Ex 8.4, drop a comment below and we will get back to you at the earliest.

On this page, you will find Data Handling Class 7 Notes Maths Chapter 3 Pdf free download. CBSE NCERT Class 7 Maths Notes Chapter 3 Data Handling will seemingly help them to revise the important concepts in less time.

CBSE Class 7 Maths Chapter 3 Notes Data Handling

Data Handling Class 7 Notes Conceptual Facts

1. Data: The collection of informations in the form of numerical figures is called data.
Each number in a data is called observation or variate and number of times a particular observation occurs is called its frequency.

2. Range: The difference between the highest and the lowest observation in a given data is called ‘Range’.

3. Frequency distribution table: A table representing the frequency of various observations is called frequency distribution table.

4. Mean, Average or Arithmetic Mean:
\(\text { Mean }=\frac{\text { Sum of all observations }}{\text { Number of observations }}=\frac{\Sigma x_{i}}{\Sigma f_{i}}\) where i=1,2,3,…………

Mean of grouped data \(=\frac{\Sigma f_{i} x_{i}}{\Sigma f_{i}}\) i=1,2,3,…………

5. Median: When the observations are arranged in ascending or descending order, then the middle observation is called its Median.

6. Mode: The observation which occurs maximum number of times in a given data is called its ‘mode’. Mean, median
and mode are called measures of central tendency.

7. Bar graph: The representation of data in the form of bars of uniform width is called bar graph.

8. A double bar graph is used to compare the information related to two types of data.

9. Probability is a chance of happening and not happening and event.

10. The probability of an event which is certain to happen is 1. It is also called as ‘sure event’.

11. The probability of an event which is impossible to happen is 0. It is also called as ‘impossible event’.

NCERT Solutions for Class 10 Maths Chapter 12 Areas Related to Circles Ex 12.2 are part of NCERT Solutions for Class 10 Maths. Here we have given NCERT Solutions for Class 10 Maths Chapter 12 Areas Related to Circles Ex 12.2.

Board	CBSE
Textbook	NCERT
Class	Class 10
Subject	Maths
Chapter	Chapter 12
Chapter Name	Areas Related to Circles
Exercise	Ex 12.2
Number of Questions Solved	14
Category	NCERT Solutions

NCERT Solutions for Class 10 Maths Chapter 12 Areas Related to Circles Ex 12.2

Question 1.
Find the area of a sector of a circle with radius 6 cm if angle of the sector is 60°.
Solution:
Radius of the sector (r) = 6 cm
Central angle of the sector = 60°

Question 2.
Find the area of a quadrant of a circle whose circumference is 22 cm.
Solution:
Let radius of the circle = r
∴ Circumference of the circle = 2πr

Question 3.
The length of the minute hand of a clock is 14 cm. Find the area swept by the minute hand in 5 minutes.
Solution:
Length of minute hand of the clock = 14 cm

Question 4.
A chord of a circle of radius 10 cm subtends a right angle at the centre. Find the area of the corresponding:
(i) minor segment
(ii) major segment (Use ? = 3.14)
Solution:
Given: radius of the circle = 10 cm
Angle subtended by chord at centre = 90°
(i) Area of the minor segment

(ii) Area of the major segment = Area of the circle – Area of the minor segment
= πr² – 28.5 = 3.14 x 10 x 10-28.5
= 314-28.5 = 285.5 cm²

Question 5.
In a circle of radius 21 cm, an arc subtends an angle of 60° at the centre. Find:
(i) length of the arc.
(ii) area of the sector formed by the arc.
(iii) area of the segment formed by the corresponding chord.
Solution:
Radius of the circle = 21 cm
Angle at the centre = 60°

Question 6.
A chord of a circle of radius 15 cm subtends an angle of 60° at the centre. Find the areas of the corresponding minor and major segments of the circle. (Use π = 3.14 and \(\sqrt{3}\) = 1.73)
Solution:
Radius of the circle = 15 cm
Angle subtended by chord at centre = 60°
Area of the sector = \(\frac{\pi r^{2} \theta}{360^{\circ}}\) = 3.14 x \(\frac{15 \times 15 \times 60^{\circ}}{360^{\circ}}\) = 117.75 cm²
Area of the triangle formed by radii and chord = \(\frac { 1 }{ 2 }\)r²θ
= \(\frac { 1 }{ 2 }\)(15)² sin 60° = \(\frac { 1 }{ 2 }\) x 15 x 15 x \(\frac{\sqrt{3}}{2}\) = 97.31 cm²
Area of the minor segment = Area of the sector – Area of the triangle formed by radii and chord
= 117.75 – 97.31 = 20.44 cm²
Area of the circle = πr² = 3.14 x 15 x 15 = 706.5 cm²
Area of the circle – Area of the minor segment
= 706.5 – 20.44 = 686.06 cm²

Question 7.
A chord of a circle of the radius 12 cm subtends an angle of 120° at the centre. Find the area of the corresponding segment of the circle. (Use π = 3.14 and \(\sqrt{3}\) = 1.73).
Solution:
Radius of the circle = 12 cm
Angle subtended by chord at centre = 120°

Area of the corresponding segment = Area of the sector – Area of A formed by radii and chord
= 150.72 – 62.28 cm² = 88.44 cm²

Question 8.
A horse is tied to a peg at one corner of a square shaped grass field of side 15 m by means of a 5 m long rope (see figure). Find

(i) the area of that part of the field in which the horse can graze.
(ii) the increase in the grazing area if the rope were 10 m long instead of 5 m. (Use n = 3.14)
Solution:
(i) Length of the rope = Radius of the sector grazed by horse = 5 m
Here, angle of the sector = 90°

Length of the rope is increased from 5 m to 10 m
New radius of sector grazed by horse = 10 m

Question 9.
A brooch is made with silver wire in the form of a circle with diameter 35 mm. The wire is also used in making 5 diameters which divide the circle into 10 equal sectors as shown in figure.

Find:
(i) the total length of the silver wire required.
(ii) the area of each sector of the brooch.
Solution:
Length of one diameter = 35 mm
Total length of 5 diameters = 5 x 35 mm = 175 mm
Circumference of the circle = 2π = 2 x \(\frac { 22 }{ 7 }\) x \(\frac { 35 }{ 2 }\) = 110 mm
(i) Total length of the wire used = length of 5 diameters + circumference of brooch
= 175 + 110 = 285 mm

(ii) Total sectors are 10.

Question 10.
An umbrella has 8 ribs which are equally spaced (see figure). Assuming umbrella to be a flat circle of radius 45 cm, find the area between the two consecutive ribs of the umbrella.

Solution:
Radius of the circle = 45 cm
Number of ribs = 8

Question 11.
A car has two wipers which do not overlap.
Each wiper has a blade of length 25 cm sweeping through an angle of 115°. Find the total area cleaned at each sweep of the blades.
Solution:
Given: length of blade of wiper = radius of sector sweep by blade = 25 cm
Area cleaned by each sweep of the blade = area of sector sweep by blade
Angle of the sector formed by blade of wiper =115°

Question 12.
To warn ships for underwater rocks, a lighthouse spreads a red coloured light over a sector of angle 80° to a distance of 16.5 km. Find the area of the sea over which the ships are warned. (Use π = 3.14)
Solution:
Angle of the sector = 80°
Distance covered = 16.5 km
Radius of the sector formed = 16.5 km

Question 13.
A round table cover has six equal designs as shown in the figure. If the radius of the cover is 28 cm, find the cost of making the designs at the rate of ₹ 0.35 per cm². (Use \(\sqrt{3}\) = 1.7)

Solution:
Radius of the cover = 28 cm
∵ There are six equal designs

Question 14.
Tick the correct answer in the following: Area of a sector of angle p (in degrees) of a circle with radius R is
(a) \(\frac{p}{180^{\circ}}\) × 2πR
(b) \(\frac{p}{180^{\circ}}\) × πR²
(c) \(\frac{p}{360^{\circ}}\) × 2πR
(d) \(\frac{p}{720^{\circ}}\) × 2πR²
Solution:
Sector angle isp in degrees
Radius of the circle = R
Area of the sector = \(\frac{\pi \mathrm{R}^{2} p}{361^{6}}\) = \(\frac{\left(\pi R^{2} p\right) 2}{720^{\circ}}\)
= \(\frac{p}{720^{\circ}}\) × 2πR²

We hope the NCERT Solutions for Class 10 Maths Chapter 12 Areas Related to Circles Ex 12.2, help you. If you have any query regarding NCERT Solutions for Class 10 Maths Chapter 12 Areas Related to Circles Ex 12.2, drop a comment below and we will get back to you at the earliest.

On this page, you will find Fractions and Decimals Class 7 Notes Maths Chapter 2 Pdf free download. CBSE NCERT Class 7 Maths Notes Chapter 2 Integers will seemingly help them to revise the important concepts in less time.

CBSE Class 7 Maths Chapter 2 Notes Fractions and Decimals

Fractions and Decimals Class 7 Notes Conceptual Facts

Fraction \(=\frac{\text { Numerator }}{\text { Denominator }}\)

1. Types of fraction:

• Proper fractions = Representing a part of a whole, e.g\(\frac{1}{2}, \frac{3}{4} \text { and } \frac{1}{4}\)
• Improper fraction: Numerator is always greater than the denominator, \(\text { e.g. } \frac{6}{5}, \frac{7}{4} \text { and } \frac{3}{2}\)
• Mixed fraction: Combination of a whole number and a proper fraction.\(\text { -e.g. } 1 \frac{2}{3}, 2 \frac{5}{6} \text { and } 3 \frac{1}{2}\)

2. Multiplication of two fractions: \(\frac{\text { Product of numerators }}{\text { Product of denominators }} \text { e.g. } \frac{2}{5} \times \frac{3}{4}=\frac{2 \times 3}{5 \times 4}=\frac{6}{20}\)

3. Reciprocal of a non-zero fraction is obtained by interchanging its numerator and the denominator e.g. reciprocal of  \(\frac{3}{4} \text { is } \frac{4}{3}\)

4. While dividing a whole number by a fraction, we multiply the whole number with the reciprocal of that
\(\text { e.g. } 5 \div \frac{3}{2}=5 \times \frac{2}{3}=\frac{10}{3}\)

5. While dividing a fraction by a whole number, we multiply the fractions by the reciprocal of the whole
\(\text { e.g. } \frac{1}{4} \div 2=\frac{1}{4} \times \frac{1}{2}=\frac{1}{8}\)

6. Division of a fraction by another fractions.

7. Multiplication of two decimal numbers: 2.25 x 1.2 = 2.700

8. Number obtained by dividing a non-zero integer by 0, is not defined, e.g. \(\text { e.g. } \frac{2}{0}, \frac{\frac{3}{2}}{0} \text { and } \frac{-5}{0}\)

On this page, you will find Integers Class 7 Notes Maths Chapter 1 Pdf free download. CBSE NCERT Class 7 Maths Notes Chapter 1 Integers will seemingly help them to revise the important concepts in less time.

CBSE Class 7 Maths Chapter 1 Notes Integers

Integers Class 7 Notes Conceptual Facts

1. Number line

For a positive integer on number line, we move towards right of zero and for a negative integer, we move towards the left of the zero.

2. Integers are closed under addition, subtraction and multiplication.
For example:

• a + b = integer
• a – b = integer
• a x b = integer

3. Addition and multiplication are cumulative for integers.
For example:

• a + b = b + a
• a x b = b x a

4. Addition and multiplication are associative for integers.
For example:

• (a + b) + c = a + (b + c)
• (a x b) x c = a x (b x c)

5. Zero (0) is an additive identity for integers.
For example: a + 0 = 0 + a = a

6. One (1) is a multiplicative identity for integers.
For example: a x 1 = 1 x a = a

7. Algebra of integers,

• a x (-b) = -ab
• (-a) xb = -ab
• (-a) x (-b) = ab
• a xb = ab

8. Product of even number of negative integers is positive whereas the product of odd number of negative integers is negative. For example:

• (-a) x (-b) x (-c) x (-d) (-e) -a x b x c x d x e …. even number times
• (-a) x (-b) x (-c) x (-d) (-e) = -(a x b x c x d x e) odd number times

9. Division on integers:
(i) \(\frac{(-a)}{(b)}=-\left(\frac{a}{b}\right)\)
(ii) \(\frac{(-a)}{(-b)}=\left(\frac{a}{b}\right)\)
(iii) \(\frac{(a)}{(-b)}=-\left(\frac{a}{b}\right)\)
(iv) \(\left(\frac{+a}{+b}\right)=\left(\frac{a}{b}\right)\)

 

On this page, you will find Pollution of Air and Water Class 8 Notes Science Chapter 18 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 18 Pollution of Air and Water will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 18 Pollution of Air and Water

Pollution of Air and Water Class 8 Notes Understanding the Lesson

1. Agents or substances that pollute water, air or soil are called pollutants.

2. The term air pollution is defined as the accumulation of harmful substances or increase in the quantity of any gas in the air above the normal level.

3. Air pollution is harmful for human beings also.

4. In the earth’s atmosphere there is about 78% of nitrogen, 21% of oxygen and the rest are other gases like CO₂, methane, ozone and water vapour.

5. The substances which contaminate the air are called air pollutants.

6. There are natural as well as man-made sources of air pollution.

7. Smoke and fog combines to form smog. Smoke may contain oxides of nitrogen which combine with other pollutants and fog to form smog.

8. Smog causes breathing difficulties.

9. Chlorofluorocarbons (CFCs) which are used in refrigerators, air conditioners and aerosol sprays damages ozone layer of the atmosphere.

10. Some pollutants like SO₂ and NO₂ react with water vapour present in the air to form sulphuric acid and nitric acid. These acids come down with rain as acid rain.

11. A part of the radiation of the sun that falls on the earth is absorbed by it, whereas a part is reflected back into space. A part of the reflected radiation is trapped by the atmosphere. This trapping of radiations by the earth’s atmosphere causes warming of the earth and this is known as greenhouse effect.

12. Human activities contribute to the accumulation of CO₂ in the atmosphere. CO₂ traps heat and does not allow it to escape into space. As a result of this, the average temperature of the earth’s atmosphere increases gradually and this is called global warming.

13. Gases which contribute to global warming, like CO₂, methane, nitrous oxide and water vapour are called greenh’ouse gases.

14. The substances that pollute water are called water pollutants.

15. The harmful substances such as sewage, toxic chemicals, silt, etc., get mixed with water and this leads to water pollution.

16. Water which is suitable for drinking is called potable water.

17. Chlorination is a commonly used chemical method for purifying water. It is done by adding chlorine tablets ‘ or bleaching powder to the water.

18. We must conserve water as it is a precious natural resource.

Class 8 Science Chapter 18 Notes Important Terms

Air pollution: When some unwanted substances get mixed with air and have harmful effect on both living and non-living things, is known as air pollution.

Chemical contamination: Presence of harmful chemicals in air, water and soil causing pollution of water is called chemical contamination.

Global warming: Due to the increasing levels of greenhouse gases, like CO₂, the average temperature of earth’s atmosphere is gradually increasing. This is called global warming.

Greenhouse effect: The process of trapping of radiations by the Earth’s atmosphere due to increasing levels of gases like CO₂ is called greenhouse effect.

Pollutants: The substances which causes pollution are known as pollutants.

Potable water: Water which is purified and is also fit for drinking is known as potable water.

Water pollution: The contamination of clean water by substances which are harmful to life is called water pollution.

On this page, you will find Stars and the Solar System Class 8 Notes Science Chapter 17 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 17 Stars and the Solar System will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 17 Stars and the Solar System

Stars and the Solar System Class 8 Notes Understanding the Lesson

1. The science dealing with the study of the universe is called astronomy.

2. The scientist who study the universe are called astronomers.

3. The stars, the planets, the moon and many other objects in the sky are called celestial objects.

4. The various shapes of the bright part of the moon as seen during a month are called phases of the moon.

5. The phases of the moon occur because we can see only that part of the moon which reflects the light of the sun towards us.

6. The stars are hot glowing spheres that continuously emit their own heat and light, that is they are self luminous objects.

7. Stars appear to move from east to west.

8. The group of stars that move together and form a characteristic pattern in the sky is called constellation.

9. There are many types of constellations like Ursa Major, Ursa Minor, Orion.

10. The sun and the celestial bodies which revolve around it form the solar system. It consists of large number of bodies such as planets, comets, asteroids and meteors.

11. The sun is the nearest star from us. It continuously emits huge amounts of heat and light.

12. A planet has a definite path in which it revolves around the sun. This path is called orbit.

13. There are total eight planets in our solar system.

14. There is a large gap in between the orbits of Mars and Jupiter. This gap is occupied by a large number of small objects that revolve around the sun. These are called asteroids.

15. Comets are also members of our solar system. They revolve around the sun, in highly elliptical orbits. A comet appears generally as a bright head with a long tail.

16. Meteors are the pieces made of stones or metals or both that move very fast in space. They are also called as ‘shooting stars’.

17. Some meteors are so big in size that they do not burn up completely in the atmosphere and reach the earth’s surface. They are called meteorites.

18. A satellite is defined as a heavenly body that moves around another heavenly body along its own orbit.

19. There are two types of satellites:

• Natural satellite
• Artificial satellite

20. Aryabhatta was the first Indian satellite. Some other Indian satellites are INSAT, IRS, Kalpana, EDUSAT, etc.

21. Artificial satellites have many practical applications. They are used for forecasting weather, transmitting television and radio signals. They are used for telecommunication and remote sensing.

Class 8 Science Chapter 17 Notes Important Terms

Artificial satellite: The satellites other than natural satellites are known as artificial satellites. They are used for forecasting weather, transmitting television and radio signals.

Asteroids: Asteroids are small bodies revolving around the sun mostly between the orbits of Mars and Jupiter.

Cassiopeia: Cassiopeia is another prominent constellation in the northern sky. It is visible during winter in the early part on the night.

Celestial objects: Objects such as stars, the planets, the moon and many other objects in the sky are called celestial objects.

Comets: Comets are small, icy objects that orbits the sun and has a long tail of gas. They revolve around the sun in highly elliptical orbits.

Constellations: The group of stars that move together and form a characteristic pattern in the sky are called constellations.

Light year: The distance travelled by light in one year is known as light year.

Meteorites: Some meteors are so large that a part of them reaches the surface of the Earth before they evaporate completely. These are called meteorites.

Meteors: A meteor is a small heavenly object moving around the sun. When a meteor occasionally enters the Earth’s atmosphere it gets heated up because of friction and glows but evaporates in a very short period of time.

Natural satellites: A natural celestial body revolving around another celestial body is called natural satellites.

Orbit: A planet revolves around the sun in a definite path. This path is known as orbit of the planet.

Orion: Orion is a constellation which contain 7 or 8 stars. It looks like a hunter.

Phases of Moon: The various shapes of the bright part of the moon as it is seen during a month are called phases of moon.

Planets: The celestial bodies that revolve around the sun in a well defined orbit are known as planets.

Pole star: The only star which always appears to remain at the same position in the sky is known as pole star.

Remote sensing: It is scanning of the earth by artificial satellite for collecting information from distance.

Solar system: The sun and the celestial bodies which revolve in the space form the solar system.

Stars: Stars are the celestial bodies which emit light of their own. The sun is also a star.

Ursa Major: Ursa major is a constellation which constitutes seven stars and is also known as ‘SaptarishV.

On this page, you will find Light Class 8 Notes Science Chapter 16 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 16 Light will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 16 Light

Light Class 8 Notes Understanding the Lesson

1. Light is a form of energy.

2. When light reaches our eyes after striking an object, we are able to see an object.

3. The bouncing back of light into the same medium after it falls on a surface is called reflection.

4. The ray of light striking the surface is called an incident ray.

5. The ray of light which is returned back into the same medium is known as the reflected ray.

7. The perpendicular drawn to the reflecting surface at the point where incident ray strikes the mirror is called normal.

8. The angle between the incident ray and the normal is called the angle of incidence.

9. The angle between the reflected ray and the normal is called the angle, of reflection.

10. Laws of reflection:

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

 

 

11. When all the parallel rays reflected from a plane surface are not parallel, the reflection is known as irregular reflection.

12. The reflection of light from a smooth and polished surface is known as regular reflection.

13. Two mirrors inclined to each other give multiple images.

14. Kaleidoscope is a device based on the principle of multiple reflections.

15. Sunlight is referred to as white light which consists of seven colours.

16. Splitting of white light into its constituent colours is called dispersion.

15. The human eye is an important sense organ that enables us to see the world around us. It is nearly spheri¬cal in shape.

16. Important parts of the eye are cornea, iris, pupil, lens, retina and optic nerve.

17. Blind spot is a portion on the retina where the nerve fibres enter the optic nerve. The image falling on the portion can’t be seen.

18. A normal eye can see nearby and distant objects clearly.

19. Long-sightedness or hypermetropia is a defect of the eye where the person cannot clearly see the nearby objects while in short-sightedness or myopia, the far-away objects can not be seen clearly. Visually challenged persons can read and write using the Braille system.

20. Visually challenged persons develop their other senses more sharply to improve their interaction with their environment.

Class 8 Science Chapter 16 Notes Important Terms

Angle of incidence: The angle between the incident ray and the normal is called the angle of incidence.

Angle of reflection: The angle between the reflected ray and the normal is called the angle of reflection.

felind spot: The portion on the retina where the nerve fibres enter the optic nerve is called blind spot. The image falling on this portion can’t be seen.

Braille: The system of representing characters by raised dots which enables the blind person to read is called Braille.

Cones: Visual receptor cells in retina, which are sensitive to bright light and sense colour are called cones.

Cornea: The transparent front part of the eye is called cornea.

Diffused/Irregular reflection: When all the parallel rays reflected from a plane surface are not parallel, the reflection is known as irregular/diffused reflection.

Dispersion: The splitting of light into its constituent colours is known as dispersion.

Incident ray: The ray of light striking the surface is called as incident ray.

Iris: The dark muscular structure behind the cornea is called iris.

Kaleidoscope: A device based on the principle of multiple reflections is called kaleidoscope.

Lateral inversion: The phenomenon of changing side, i.e, left to right and right to left by the mirror while forming an image is called lateral inversion.

Pupil: The small opening in the cornea is called pupil.

Reflected rays: The rays of light which returns back from the surface after reflection is known as refl ected ray.

Reflection: The bouncing back of light into the same medium after it falls on a surfac is called reflection.

Regular reflection: When all the parallel rays reflected from a smooth and polished surface is also parallel is called regular reflection.

Retina: The site where the image is formed in the eye is called retina.

Rods: The nerve cells on retina which are sensitive to dim light are called rods.

On this page, you will find Some Natural Phenomena Class 8 Notes Science Chapter 15 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 15 Some Natural Phenomena will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 15 Some Natural Phenomena

Some Natural Phenomena Class 8 Notes Understanding the Lesson

1. Lightning is an electric spark on a huge scale. It is caused by the accumulation of charges in the clouds.

2. Some objects can be charged by rubbing with other objects. These objects are called charged objects.

3. There are two types of charges – positive and negative.

4. The charge acquired by a glass rod when it is rubbed with silk is called positive.

5. The charge on an ebonite rod when rubbed with fur, wool or flannel is considered as negative.

6. The electric charges generated by rubbing are called static charges.

7. When charges move they constitute an electric current. Thus, moving charges are called current.

8. Like charges repel each other and unlike charges attract each other.

9. A device used to test whether an object is carrying charge or not is called an electroscope.

10. Electric charge can be transferred from a charged object to another through a metal conductor.

11. The process of transferring of charge from a charged object to the earth is called earthing.

12. When a body loses charges to the earth or any other it is said to be discharged.

13. The process of electric discharge between clouds and the earth or between different clouds causes lightning.

14. Lightning strike could destroy life and property. It is, therefore, necessary to take measures to protect ourselves.

15. During lightning and thunderstorm no open place is safe. A house or a building is a safe place. During travelling by car or by bus, it is safe to stay inside with windows and doors of the vehicle shut. Carrying an umbrella is not at all a good idea during thunderstorm. If in a forest, shelter should be taken under shorter trees.

16. Lightning can strike telephone cords, electrical wires and metal pipes. Electrical appliances like computer, TV, etc., should be unplugged. Electrical lights can remain on.

17. Lightning conductor is a device used to protect buildings from the effect of lightning.

18. An earthquake is a sudden shaking or trembling of the earth. It lasts for a very short time. It is caused by a disturbance deep inside the earth’s crust.

19. Earthquake can cause a great loss to our life and property. It can cause immense damage to buildings, bridges, dams and people. It can also cause floods, landslides and tsunamis.

20. Unfortunately, we are not yet able to predict an earthquake accurately.

21. The power of an earthquake is expressed in terms of a magnitude on a scale called the Richter scale.

22. Earthquakes having magnitudes higher than 7 on the Richter scale cause a great destruction to our life and property.

23. Earthquakes are caused by the movement of plates, the boundaries of the plates are the weak zones where earthquakes are more likely to occur. The weak zones are known as seismic or fault zones.

24. We should adopt precautionary and protective measures to save ourselves from the upcoming damages of an earthquake.

Class 8 Science Chapter 15 Notes Important Terms

Crust: The uppermost layer of Earth’s surface (8 km – 32 km) is termed as crust.

Discharge: Discharge is the release or transmission of charges from one object to another through a medium like liquid, gas or solid.

Earth’s plates: The outermost layer of the earth is fragmented. Each fragment is called a plate.

Earthquake: An earthquake is a sudden shaking or trembling of the earth which lasts for a very short time. It is caused by deep disturbances caused by movement of earth’s plates inside the earth’s crust.

Electroscope: It is a device used to test whether an object is charged or not.

Lightning: It is the process of electric discharge between cloud and the earth or between different clouds.

Lightning conductor: It is a device used to protect buildings from the effect of lightning. A metallic rod, taller than the building, is installed on the roof of elevated structure.

Negative charge: The charge of an object due to excess of electrons is called negative charge.

Positive charge: The charge of an object due to loss of electrons is called positive charge.

Richter scale: The power of an earthquake is expressed in terms of a magnitude on a scale called Richter scale.

Seismograph: It is an instrument which measures and records the magnitude of an earthquake in terms of the shock waves it produces.

Thunder: The loud noise accompanied by lightning is called thunder.

Thunderstorm: A storm accompanied by thunder and lightning is called thunderstorm.

Transfer of charge: Electric charges can be transferred from a charged object to another through a metal conductor.

Tsunami: A sudden violent change in the earth’s surface resulting from a destructive sea wave caused by an earthquake or volcanic eruption is known as tsunami. Coastal areas around the ocean suffer huge Mosses.

Tremor: A small earthquake is called tremor.

On this page, you will find Sound Class 8 Notes Science Chapter 13 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 13 Sound will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Chapter 13 Notes Sound

Sound Class 8 Notes Understanding the Lesson

1. Sound is defined as a form of energy that travels through medium in the form of vibrations.

2. A sound can be produced by:

• beating
• rubbing
• blowing
• plucking

3. The movement that produces sound in rapid to and fro motion is called vibration.

4. Sound requires medium to travel. Sound can travel through solids, liquids and gases but not through vacuum.

5. Sound travel fastest in solid and slowest in gases.

6. In human beings, the sound is produced by the voice box or the larynx.

7. Voice box is located at the upper end of the windpipe.

8. The eardrum senses the vibration of sound and sends the signal to the brain. This process is called hearing.

9. A vibration has three important characteristics – frequency, amplitude and time period.

10. Frequency is defined as the number of vibrations made by a vibrating body in one second. Its unit is hertz (Hz).

11. Amplitude is defined as the maximum extent to which a vibrating body can vibrate.

12. Time period is defined as the time taken by a vibrating body for one complete vibration.

13. Loudness is the characteristic of sound that enables us to distinguish a loud sound from low sound.

14. Pitch is a characteristic of sound that enables us to distinguish a shrill sound from the grave (hoarse) sound.

15. The term quality is defined as the characteristic of sound by virtue of which we can easily differentiate the two sounds of same pitch.

16. The unwanted and unpleasant sound that causes discomfort is called noise.

17. The sound that we enjoy from musical instruments are called musical sound.

18. Presence of excessive or unwanted sounds in the environment is called noise pollution.

19. Plantation on the roadside and elsewhere can reduce noise pollution.

Class 8 Science Chapter 13 Notes Important Terms

Amplitude: is defined as the maximum extent to which a vibrating body can vibrate.

Audible: The type of sounds which we are able to hear are called audible sounds.

Eardrum: Eardrum is a thin membrane through which the sound waves passed.

Hertz: The frequency is expressed in hertz (Hz).

Larynx: Larynx is the organ which produces sound in the human being. It is also called voice box.

Loudness: Is the characteristic of sound that enables us to distinguish a loud sound from low sound.

Noise: The sound which are unpleasant to hear are termed as noise.

Oscillation: The to and fro motion of the vibrating particles about its mean position is called oscillation.

Pitch: The characteristic of sound by which we distinguish between different sounds of the same loudness is known as pitch.

Shrillness: The property of sound that depends upon frequency of vibrating object is known as shrillness.

Time period: The time taken by the bob of the pendulum to complete one oscillation, is called its time period.

Ultrasonic sound: The sound which have frequencies greater than 20,000 Hz is called ultrasonic sound.

Vibration: The movement of a body from one extreme position to the other is termed as vibration.

Voice box: It is that part by which sound is produced in humans.

Windpipe: The pipe which connects the larynx with the lungs is called windpipe.

On this page, you will find Chemical Effects of Electric Current Class 8 Notes Science Chapter 14 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 14 Chemical Effects of Electric Current will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Chapter 14 Notes Chemical Effects of Electric Current

Chemical Effects of Electric Current Class 8 Notes Understanding the Lesson

1. The substances that allow the electric current to pass through them are called conductors; e.g., copper, aluminium, etc.

2. The substances that do not allow the electric current to pass through them are called insulators; e.g., I rubber, plastic, wood, etc.

3. Some liquids are good conductors of electricity and some are poor conductors.

4. Most liquids that conduct electricity are solutions of acids, bases and salts.

5. Pure or distilled water is free of salts and thus act as insulator or a bad conductor of electricity. Water from tap, handpumps, wells, etc., is not pure but a solution. It contains small amount of mineral salts dissolved in it. This water is thus a good conductor of electricity.

6. Common salts when dissolved in distilled water, makes it a good conductor.

7. The passage of an electric current through a conducting solution causes chemical reactions such as formation of bubbles of a gas on the electrodes, deposits of metals on the electrodes, changes of colour of solutions, etc., is known as chemical effects of current.

8. Electroplating is one of the most common application of chemical effects of current. It is the process of depositing a layer of any desired metal on another material by means of electricity.

9. Electroplating is done to make objects shiny in appearance, resistant to scratches and corrosion.

Class 8 Science Chapter 14 Notes Important Terms

Electrode: An electrode is a conductor that allows electric current to pass from one medium to another using the graphite or metal plates or rods.

Electroplating: The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating. It is done by using an electrolytic cell.

Good conductor: The materials which allow electric current to pass through them are called good conductors of electricity; e.g., copper, aluminium, etc.

Poor conductor: The materials which do not allow electric current to pass through them are called poor or bad conductors of electricity. They are also known as insulators; e.g., rubber, plastic, wood, etc.

LED: It is an electronic device containing two wires called leads, one lead (longer) is connected to the positive (+) terminal and the other (smaller) to the negative (-) terminal of the battery. It starts emitting light even when a very weak current flows through it. It is actually Light Emitting Diode.