Reflection of light-full notes

Introduction

• Light is a form of energy due to which we are able to see the objects which emits light for example objects like sun, lamp, candle emits light of their own and thus they are known as luminous objects.
• There are objects like table , chair etc. which are not luminous objects and still we are able to see them and this happens because they reflects lights which falls on them from a luminous object like sun, lamp etc. and when this reflected light reaches our eyes we are able to see such non luminous objects.
• Light rays basically consist of electromagnetic waves which do not require any material medium (like solid, liquid or gas) for their propagation.
• The wavelength of visible light waves is very small and is of the order of  to .
• Speed of light waves depends on the medium through which they pass as speed of light in air is slightly less than the speed of light in vacuum  same way speed of light in water and glass is much less than that in air.
• When light falls on the surface of an object it can either be
  1. Absorbed:- If an object absorbs all the light falling on it , then it will appear perfectly black for example a blackboard
  2. Transmitted: - An object is said to transmit light if it allows light to pass through itself and such objects are transparent.
  3. Reflected:- If an object sends back light rays falling on its surface then it is said to have reflected the light

Reflection of Light

• The process of sending back light rays which falls on the surface of an object is called REFLECTION of light
• Silver metal is one of the best reflectors of light.
• Mirrors we use on our dressing tables in our home are plane mirrors.
• A ray of light is the straight line along which the light travelled and a bundle of light rays is called a beam of light.
• Laws of Reflection of light
  1. The angle of incidence is equal to the angle of reflection, and
  2. The incident ray, the reflected ray and the normal to the mirror at the point of incidence all lie in the same plane.
• These laws of reflection are applicable to all types of reflecting surfaces including spherical surfaces  
• Real and Virtual images

• An image is formed when the light rays coming from an object meet at a point after reflection from a mirror (or refraction from lens).
• The images are of two types
  
  1. Real Images:- Real images are formed when rays of light that comes from an object (or source) meets at a point after reflection from a mirror (or refraction from a lens). Real images can be formed on a screen and can be seen with the eyes.
  2. Virtual images:- Virtual image is an image in which the outgoing rays from an object do not meet at a point. It will appear to meet at a point in or behind the optical device (i.e., a mirror) but they do not actually meet after reflection from a mirror (or refraction from a lens). A plane mirror always forms virtual images.

Characteristics of images formed by mirrors:-

(a) Images formed by mirrors are always virtual and erect
(b) Size of image is always equal to the size of the object and the image is laterally inverted.
(c) The images formed by the plane mirror are as far behind the mirror as the object in front of the mirror.

• Lateral inversion:- If an object is placed in front of the mirror, then the right side of the object appears to be the left side and left side of the object appears to be the right side of this image. This change of sides of an object and its mirror image is called lateral inversion.

  Image Formation by Spherical mirrors

  • The nature, position and size of the image formed by a concave mirror depend on the position of the object in relation to points P, F and C.
  • The image formed can be real as well as virtual depending on the positions of the object.
  • The image is either magnified, reduced or has the same size, depending on the position of the object.

  Rules for obtaining images formed by spherical mirrors

  (1) Rule 1

  A ray of light which is parallel to the principle axis of the mirror passes through its focus after reflection from the mirror as shown below in the figure
  
  From the figure given above it can be clearly seen that the light rays passes through principle focus in case of concave mirrors and appears to diverge from principle focus in case of concave mirror.

  (2) Rule 2

  A ray of light passing through the centre of curvature of the curvature of the concave mirror or directed in the direction of the centre of curvature of a convex mirror, is reflected back along the same path as shown below in the figure
  
  This happens because the incident rays fall on the mirror along the normal to the reflecting surface.

  (3) Rule 3

  A ray passing through principle focus of a concave mirror or a ray which is directed towards the principal focus of a convex mirror, becomes parallel to the principle axis after reflection and is shown below in the figure
  
  

  (4) Rule 4

  A ray incident obliquely to the principal axis, towards a point P (pole of the mirror), on the concave mirror or a convex mirror, is reflected obliquely. The incident and reflected rays follow the laws of reflection at the point of incidence (point P), making equal angles with the principal axis and is shown below in the figure
  

  Image formation by concave mirror

  • The type of image formed by a concave mirror depends on the position of the object kept in front of the mirror. We can place the object at following places
    1. Between pole P and focus F
    2. At the focus
    3. Between focus F and centre of curvature C
    4. At the centre of curvature
    5. Beyond center of curvature
    6. At far off distances called infinity and cannot be shown in the figures
  • Image formation by a concave mirror for different positions of the object is shown below in the table 
  • Concave mirrors are used as shaving mirrors, reflectors in car headlights, hand torch and table lamps.
  • Large concave mirrors are used in field of solar energy to focus sun rays on objects to be heated.

  Image formation by convex mirrors

• In order to construct a ray diagram to find out the position, nature and size of image formed by convex mirror we should remember following path of rays of light.
• A ray of light parallel to the principle axis of a convex mirror appears to be coming from its focus after reflection from the mirror.
• A ray of light going towards the centre of curvature of convex mirror is reflected back along its own path.
• Convex mirrors have its focus and center of curvature behind it and no light can go behind the convex mirror and all the rays that we show behind the convex mirror are virtual and no ray actually passes through the focus and center of curvature of the convex mirror.
• Whatever be the position of object in front of convex mirror, the image formed by a convex mirror is always behind the mirror, virtual, erect and smaller than the object.
• Nature, position and relative size of the image formed by a convex mirror is given below in the table 
• Convex mirrors are used as rear view mirrors in automobiles to see the traffic at back side as they give erect images and also highly diminished one giving the wide field view of traffic behind.

  Sign convention for reflection by spherical mirrors

  Reflection of light by spherical mirrors follow a set of sign conventions called the New Cartesian Sign Convention. In this convention, the pole (P) of the mirror is taken as the origin. The principal axis of the mirror is taken as the x-axis (X’X) of the coordinate system. The conventions are as follows –
  
  • The object is always placed to the left of the mirror. This implies that the light from the object falls on the mirror from the left-hand side.
  • All distances parallel to the principal axis are measured from the pole of the mirror.
  • All the distances measured to the right of the origin (along + x-axis) are taken as positive while those measured to the left of the origin (along – x-axis) are taken as negative.
  • Distances measured perpendicular to and above the principal axis (along + y-axis) are taken as positive.
  • Distances measured perpendicular to and below the principal axis (along –y-axis) are taken as negative.
  These new Cartesian sign convention for spherical mirrors are shown below in the figure 

  Mirror formula and magnification

  Mirror formula:-

  It gives the relationship between image distance (v) , object distance (u) and the focal length (f) of the mirror and is written as
  
  Where v is the distance of image from the mirror, u is the distance of object from the mirror and f is the focal length of the mirror. This formula is valid in all situations for all spherical mirrors for all positions of the object.

  Magnification

  Magnification produced by a spherical mirror gives the relative extent to which the image of an object is magnified with respect to the object size. It is expressed as the ratio of the height of the image to the height of the object. It is usually represented by the letter m. So, 
  or,
  
  The magnification m is also related to the object distance (u) and image distance (v) and is given as 
   

Metals and non metals important questions

Question-1
a) Due to which property of metals are metallic foils prepared?
b) Write uses of aluminium foils
Solution:
a) Metallic foils are prepared, making use of the malleable property of metals.
b) Aluminium foils are used for
(i) wrapping chocolates and food stuff
(ii) to prepare hydrogen.

Question-2
Name one non-metal and one metal, which are in liquid state at room temperature.
Solution:
Bromine is the non–metal and mercury is the metal which are in liquid state at room temperature.

Question-3
Give reasons for the following
i) Zinc oxide is considered an amphoteric oxide.
ii) Non-metals in general do not displace hydrogen from dilute acids.
iii) Metals conduct electricity.
Solution:
i) Zinc oxide is considered an amphoteric oxide because it shows both acidic and basic behaviour.
ii) Non-metals do not react with dilute acids hence do not displace hydrogen from dilute acids.
iii) thatMetals conduct electricity because they contain free electrons which can move easily through the metal and conduct electric current.

Question-4
Identify the following oxides with neutral, acidic, basic and amphoteric oxides.
i) Al2O3 ii) MgO iii) SO2 iv) CO; v) Na2O vi) N2O vii) ZnO viii) CO2 ix) SO3 x) CaO.
Solution:
Neutral oxides: CO; N2O
Acidic oxides: SO2; CO2; SO3
Basic oxides: MgO; Na2O; CaO
Amphoteric oxides: Al2O3 ; ZnO

Question-5
By what processes do you concentrate the following ores:
i) PbS(galena)
ii) Fe2O3(haematite)
iii) Al2O3.2H2O (bauxite).
Solution:
i) PbS (galena) is concentrated by froth floatation method.
ii) Fe2O3 (haematite) is concentrated by magnetic separation.
iii) Al2O3.2H2O (bauxite) is concentrated by leaching process (chemical method).

Question-6
Why is that iron does not occur as a metal in the crust of the earth? What are the common compound forms in which iron occurs? Which of these is more often used for extracting iron? Why are carbon and limestone mixed with iron ore before feeding it into the blast furnace? Write the chemical equations for the reduction step and the slag formation step.
Solution:
Iron is quite reactive and so it does not occur as a metal in the crust of the earth. The common compounds formed are its oxide, a carbonate and a sulphide. The oxide ore of iron called haematite is more often used for extracting iron. The carbon and limestone which is mixed with iron ore is called the charge. This charge is responsible for the formation of iron metal. Coke acts the reducing agent and addition of limestone helps to remove the earthy impurities like sand from the blast furnace by forming fusible slag.
Reduction of Iron(III)oxide or haematite to Iron: carbon monoxide reduces iron(III)oxide to iron metal


Question-7
By what chemical processes do you obtain the following metals?
i) Mercury from HgO ii) Iron from Fe2O3 iii) Manganese from MnO2 iv) Sodium form NaCl v) Aluminium from Al2O3.


Question-8
i) What is the composition of molten slag, formed in the extraction of iron in the blast furnace?
ii) What is the use of slag?

Solution:
i) Molten slag in the extraction of iron is calcium silicate(CaSiO3).
ii) Slag is used for constructions of roads.

Question-9
Write the name of the compound, when iron is corroded?
Solution:
When iron is corroded rust is formed which is hydrated iron (III) oxide (Fe2O3.x.H2O)

Question-10
Give reasons for the following
i. Na, K and Ca metals form hydrides by combination with hydrogen gas, but most other metals do not.
ii. Aluminium easily combines with oxygen but still it can be used for making kitchen utensils.
Solution:
i. Metals like Na, K and Ca can force the hydrogen atoms to accept electrons given by them and form hydrides.
ii. Aluminium forms a protective oxide layer when it combines with oxygen and hence it is used for making kitchen utensils.

Question-11
i) Among iron and aluminium which rusts easily?
ii) What are the conditions, necessary for rusting of iron?
Solution:
i) Among iron and aluminium, iron rusts easily. It forms Al2O3. That is why iron pi

Acids,bases and salts questions -1

1.What is an acid?

An acid is a hydrogen-containing chemical compound which, when dissolved in water, gives hydrogen ion (H+) or hydrated hydrogen ion (H2O. H+) or hydronium ion (H3O+).

2.What are bases and alkalies?

Oxides and hydroxides of metals and metal like radicals (e.g., NH4+ ions) are called bases. Bases ionise to give OH– ions in aqueous solution. Bases may be soluble or insoluble in water. The soluble bases are called alkalies. Thus all alkalies are bases but all bases are not alkalies.
Examples
NaOH and Cu (OH)2 both are bases, but, since NaOH is soluble in water, it is an alkali. On the other hand, since Cu (OH)2 is insoluble in water, it is not an alkali. Other examples of alkalies are KOH, Ca (OH)2 and NH4OH.

3.Define pH.

pH of a given solution is the negative logarithm to the base 10 of the hydrogen ion concentration, [H+] expressed in g ions/lit or moles/lit. Thus
pH=- log1- [H+].

4.What are the practical applications of neutralisation reactions?

Being alkaline in nature, cold milk is used to neutralise the acidity produced by HCl present in the gastric juice in the stomach.
Astronauts in space ships use this reaction to neutralise the dangerous levels of CO2.
Farmers add slaked lime (calcium hydroxide) to reduce acidity of soil.
Sting of ants and bees contains formic acid. This can be neutralised by rubbing soap, which contains free sodium hydroxide.
Persons suffering from acidity are given antacid tablets, containing magnesium hydroxide which neutralises excess HCl produced, in stomach. Alternately, they are advised to sip cold milk, which neutralises HCl.

5.Why the salts solutions of strong acid and strong alkali are neutral?

Let us take the example of potassium sulphate, which is a salt of strong acid [sulphuric acid] and strong base [potassium hydroxide solution].
From the above equation, it is clear that water is always feebly ionised and hence solution of potassium sulphate is neutral in nature.

6.What is an universal indicator?

Universal indicator is a solution, which undergoes several colour, changes over a wide range of pH. The colour is used to ‘indicate’ pH directly. Universal indicators are usually mixtures of several indicators.

7.Why common indicators cannot determine pH value of a solution?

Common indicators, such as litmus; methyl orange and phenolphthalein can easily tell, us whether a solution is acidic or alkaline, but they cannot easily tell how much a given acidic solution is stronger than another acidic solution. It means they cannot really tell us the pH value of different acidic or alkaline solutions.
In case of litmus, we cannot tell about pH values of 5,6 and 7. Similarly, in case of methyl orange pH values between 3 and 8 will not be very accurate.

8.What are the general characteristics of acids?

They have a sour taste
They turn blue litmus to red and methyl orange to red.
They react with active metals to give hydrogen
They decompose carbonates to produced carbon dioxide and water.

9.What is called deliquescent? Give examples.

Compounds that take up enough water from the air to dissolve in the water they have taken up are called deliquescent. Calcium chloride (CaCl2) and Sodium hydroxide (NaOH) are the examples of deliquescent.

10.Write the uses of chlorines.

Chlorine is used in the production of bleaching powder.
Chlorine is used for making solvents for dry cleaning.
Chlorine is used to sterilise drinking water supply, and the water in swimming pools.
It is used in the production of hydrochloric acid.

class10 important questions our environment

IMPORTANT QUESTIONS:

   

1. Why is improper disposal of waste a curse to environment?
2. Write the common food chain of a pond ecosystem.
3. What are the advantages of cloth bags over plastic bags during shopping?
4. Why are crop fields known as artificial ecosystems?
5. Differentiate between biodegradable and non-biodegradable substances. Cite examples.
6. Suggest one word for each of the following statements/ definitions
   • (a) The physical and biological world where we live in
   • (b) Each level of food chain where transfer of energy takes place
   • (c) The physical factors like temperature, rainfall, wind and soil of an ecosystem
   • (d) Organisms which depend on the producers either directly or indirectly for food
7. Explain the role of decomposers in the environment?
8. Select the mis-matched pair in the following and correct it.
   • (a) Biomagnification — Accumulation of chemicals at the successive trophic levels of a food chain
   • (b) Ecosystem — Biotic components of environment
   • (c) Aquarium — A man-made ecosystem
   • (d) Parasites — Organisms which obtain food from other living organisms
9. We do not clean ponds or lakes, but an aquarium needs to be cleaned. Why?
10.  
11. Indicate the flow of energy in an ecosystem. Why is it unidirectional? Justify.
12. What are decomposers? What will be the consequence of their absence in an ecosystem?
13. Suggest any four activities in daily life which are eco-friendly.
14. Give two differences between food chain and food web.
15. Name the wastes which are generated in your house daily. What measures would you take for their disposal?
16. Suggest suitable mechanism (s) for waste management in fertiliser industries.
17. What are the by-products of fertiliser industries? How do they affect the environment?
18. Explain some harmful effects of agricultural practices on the environment.

class10 important questions-sources of energy

IMPORTANT QUESTIONS:


      

1. Why is there a need to harness non-conventional sources of energy? Give two main reasons.
2. Write two different ways of harnessing energy from ocean.
3. What steps would you suggest to minimise environmental pollution caused by burning of fossil fuels?
4. What is the role of a plane mirror and a glass sheet in a solar cooker?
5. Mention three advantages of a solar cell?
6. What is biomass? What can be done to obtain bio-energy using biomass?
7. What are the limitations in obtaining energy from wind?
8. Which is the process used to harness nuclear energy these days? Explain it briefly.
9. How can solar energy be harnessed? Mention any two limitations in using solar energy. How are these limitations overcome?
10. Make a list of conventional and non-conventional sources of energy. Give a brief description of harnessing one nonconventional source of energy.
11. Why is there a need for harnessing non-conventional sources of energy? How can energy be harnessed from the sea in different ways?
12. What are the environmental consequences of using fossil fuels? Suggest the steps to minimise the pollution caused by various sources of energy including non-conventional sources of energy.
13. Energy from various sources is considered to have been derived from the sun. Do you agree? Justify your answer.
14. What is biomass? Explain the principle and working of a biogas plant using a labelled schematic diagram.

class10 Our Environment key points

POINTS TO REMEMBER:

1) ECOLOGY – The study of the interaction of living organisms with each other and their surroundings is called ecology.

2) ENVIRONMENT – Everything that surrounds organisms and influences its life.

a) Biotic components of environment --- The living organisms .e.g. Plants and animals.

b) Abiotic components of environment --- The nonliving components  like water, air, light, etc.

It is the sum total of all external conditions and influences that affect the life and the development of organisms i.e.,it includes all the biotic and abiotic factors.

3) ECOSYSTEM – All interacting organisms in an area together with the nonliving constituents of environment. (Functional unit of an environment)

Functions of ecosystem:-

a) Flow of energy         b) Cycling of nutrients(bio-geo chemical cycles).

4) PRODUCERS --- They make the energy from sunlight available to the rest of the ecosystem.

5) CONSUMERS --- Animals can not manufacture their own food. They are called consumers.

6) BIODEGRABLE ---- Substances that are broken down by the action of bacteria or other saprophytes. e.g. – Paper.

7) NONBIODEGRABLE --- Substances that are not broken down by the action of bacteria or saprophytes. e. g. Plastic.

8) FOOD CHAIN -The process of one organism eating the other. 

GRASS-- > GRASSHOPPER-- >; FROG -> SNAKE

Importance of food chain

1.It helps in transfer of food energy from one organism to another.

2.It is a pathway for the flow of energy.

3. It helps in understanding the interdependence amongst different organisms.

Trophic levels are the various steps in the food chain .

Producers --- first trophic level                   Herbivores --- second trophic levels

Carnivores --- third trophic level               Top carnivores --- fourth trophic level

9) FOODWEB ----- It is a network of food links between populations in a community.

10) FLOW OF ENERGY -Ten percent law Energy available at each successive trophic level is 10 % of the previous level. (Lindeman 1942)

The law states that, “ only a 10 % amount of the total available energy is transferred from one trophic level to the next. The rest 90% of energy is used up or lost to the surrounding.”

11) BIOLOGICAL MAGNIFICATION --- Progressive accumulation of non- biodegradable waste at various trophic levels of food chain.

12. Differences between food chain & food web 

Food chain

1. The process of eating & being eaten to transfer food energy.  2. It forms a part of food web.

3. It has limited populations.

Food web

1. It is a system of interconnected food chains. 2. It contains many food chains.

3. It has several populations of different species.

 

13. HOW DO OUR ACTIVITIES AFFECT THE ENVIRONMENT?

Two major problems:-

a) Depletion of ozone layer

b) Disposal of waste

Good ozone and bad ozone

The thick blanket of ozone layer in the atmosphere which forms a protective cover & prevents UV radiation from reaching the earth‘s surface. This is called good ozone and is found in the stratosphere.

Ozone when present in the troposphere act as a pollutant . This harmful ozone is called bad ozone.

14. Depletion of ozone layer : The ozone layer protects all the organisms from the harmful ultra violet rays.

Ozone depleting substances: CFCs, N2O, CH4 , CCl4

These chlorine containing compounds are used in:  Aerosols, solvents, refrigerants and fire extinguishers.  Ozone hole developed over Antarctica.

15. Effects of ozone depletion on human health- Due to depletion of ozone layer UV radiations reaches the earth and cause:

i) skin cancer            ii) increased chances of cataract 

 iii) suppression of immune system . Managing the garbage we produce

16. Reasons for large production of garbage

i) Improvement in life style

ii) Changes in attitude (more things become disposable)

iii) Population explosion

iv) Changes in packaging (non -biodegradable)