Class 10 Physics Chapter wise Synopsis

Light: Reflection and Refraction

• Light seems to travel in straight lines.

 

• Mirrors and lenses form images of objects. Images can be either real or virtual, depending on the position of the object.

 

• The reflecting surfaces, of all types, obey the laws of reflection. The refracting surfaces obey the laws of refraction.

 

• New Cartesian Sign Conventions are followed for spherical mirrors and lenses.

 

• Mirror formula, 

1/v + 1/u = 1/f

, gives the relationship between the object-distance (u), image-distance (v), and focal length (f) of a spherical mirror.

 

• The focal length of a spherical mirror is equal to half its radius of curvature.

 

• The magnification produced by a spherical mirror is the ratio of the height of the image to the height of the object.

 

• A light ray travelling obliquely from a denser medium to a rarer medium bends away from the normal. A light ray bends towards the normal when it travels obliquely from a rarer to a denser medium.

 

• Light travels in vacuum with an enormous speed of 3×10⁸ m s⁻¹. The speed of light is different in different media.

 

• The refractive index of a transparent medium is the ratio of the speed of light in vacuum to that in the medium.

 

• In case of a rectangular glass slab, the refraction takes place at both air-glass interface and glass-air interface. The emergent ray is parallel to the direction of incident ray.

 

• Lens formula, 

1/v - 1/u = 1/f

, gives the relationship between the object-distance (u), image-distance (v), and the focal length (f) of a spherical lens.

 

• Power of a lens is the reciprocal of its focal length. The SI unit of power of a lens is dioptre.

The Human Eye and the Colourful World

• The ability of the eye to focus on both near and distant objects, by adjusting its focal length, is called the accommodation of the eye.

 

• The smallest distance, at which the eye can see objects clearly without strain, is called the near point of the eye or the least distance of distinct vision. For a young adult with normal vision, it is about 25 cm.

 

• The common refractive defects of vision include myopia, hypermetropia and presbyopia. Myopia (short-sightedness – the image of distant objects is focussed before the retina) is corrected by using a concave lens of suitable power. Hypermetropia (far-sightedness – the image of nearby objects is focussed beyond the retina) is corrected by using a convex lens of suitable power. The eye loses its power of accommodation at old age.

 

• The splitting of white light into its component colours is called dispersion.

 

• Scattering of light causes the blue colour of sky and the reddening of the Sun at sunrise and sunset.

Electricity

• A stream of electrons moving through a conductor constitutes an electric current. Conventionally, the direction of current is taken opposite to the direction of flow of electrons.

 

• The SI unit of electric current is ampere.

 

• To set the electrons in motion in an electric circuit, we use a cell or a battery. A cell generates a potential difference across its terminals. It is measured in volts (V).

 

• Resistance is a property that resists the flow of electrons in a conductor. It controls the magnitude of the current. The SI unit of resistance is ohm (Ω ).

 

• Ohm’s law: The potential difference across the ends of a resistor is directly proportional to the current through it, provided its temperature remains the same.

 

• The resistance of a conductor depends directly on its length, inversely on its area of cross-section, and also on the material of the conductor.

 

• The equivalent resistance of several resistors in series is equal to the sum of their individual resistances.

 R = R₁ + R₂ + R₃

• A set of resistors connected in parallel has an equivalent resistance R given by

1/R = 1/R₁ + 1/R₂ + 1/R₃

• The electrical energy dissipated in a resistor is given by

 

• W = V × I × t

 

• The unit of power is watt (W). One watt of power is consumed when 1 A of current flows at a potential difference of 1 V. 

• The commercial unit of electrical energy is kilowatt hour (kWh).

 1 kW h = 3,600,000 J = 3.6 × 10⁶ J.

Magnetic Effects of Electric Current

• A compass needle is a small magnet. Its one end, which points towards north, is called a north pole, and the other end, which points towards south, is called a south pole.

 

• A magnetic field exists in the region surrounding a magnet, in which the force of the magnet can be detected.

 

• Field lines are used to represent a magnetic field. A field line is the path along which a hypothetical free north pole would tend to move. The direction of the magnetic field at a point is given by the direction that a north pole placed at that point would take. Field lines are shown closer together where the magnetic field is greater.

 

• A metallic wire carrying an electric current has associated with it a magnetic field. The field lines about the wire consist of a series of concentric circles whose direction is given by the right-hand rule.

 

• The pattern of the magnetic field around a conductor due to an electric current flowing through it depends on the shape of the conductor. The magnetic field of a solenoid carrying a current is similar to that of a bar magnet.

 

• An electromagnet consists of a core of soft iron wrapped around with a coil of insulated copper wire.

 

• A current-carrying conductor when placed in a magnetic field experiences a force. If the direction of the field and that of the current are mutually perpendicular to each other, then the force acting on the conductor will be perpendicular to both and will be given by Fleming’s left-hand rule. This is the basis of an electric motor. An electric motor is a device that converts electric energy into mechanical energy.

 

• The phenomenon of electromagnetic induction is the production of induced current in a coil placed in a region where the magnetic field changes with time. The magnetic field may change due to a relative motion between the coil and a magnet placed near to the coil. If the coil is placed near to a current-carrying conductor, the magnetic field may change either due to a change in the current through the conductor or due to the relative motion between the coil and conductor. The direction of the induced current is given by the Fleming’s right-hand rule.

 

• A generator converts mechanical energy into electrical energy. It works on the basis of electromagnetic induction.

 

• In our houses we receive AC electric power of 220 V with a frequency of 50 Hz. One of the wires in this supply is with red insulation, called live wire. The other one is of black insulation, which is a neutral wire. The potential difference between the two is 220 V. The third is the earth wire that has green insulation and this is connected to a metallic body deep inside earth. It is used as a safety measure to ensure that any leakage of current to a metallic body does not give any severe shock to a user.

 

• Fuse is the most important safety device, used for protecting the circuits due to short-circuiting or overloading of the circuits.

Thanks to Watch and stay with me till last words of synopsis.

Chapter wise Synopsis Science Class 10

Chapter wise Synopsis

Class 10

Subject Science

1. Chemical Reactions And Equations.

 • A complete chemical equation represents the reactants, products and their physical states symbolically.

 

• A chemical equation is balanced so that the numbers of atoms of each type involved in a chemical reaction are the same on the reactant and product sides of the equation. Equations must always be balanced.

 

• In a combination reaction two or more substances combine to form a new single substance.

 

• Decomposition reactions are opposite to combination reactions. In a decomposition reaction, a single substance decomposes to give two or more substances.

 

• Reactions in which heat is given out along with the products are called exothermic reactions.

 

• Reactions in which energy is absorbed are known as endothermic reactions.

 

• When an element displaces another element from its compound, a displacement reaction occurs.

 

• Two different atoms or groups of atoms (ions) are exchanged in double displacement reactions.

 

• Precipitation reactions produce insoluble salts.

 

• Reactions also involve the gain or loss of oxygen or hydrogen by substances. Oxidation is the gain of oxygen or loss of hydrogen. Reduction is the loss of oxygen or gain of hydrogen.

2. Acids, Bases And Salts

• Acid-base indicators are dyes or mixtures of dyes which are used to indicate the presence of acids and bases.

 

• Acidic nature of a substance is due to the formation of H+(aq) ions in solution. Formation of OH–(aq) ions in solution is responsible for the basic nature of a substance.

 

• When an acid reacts with a metal, hydrogen gas is evolved and a corresponding salt is formed.

 

• When a base reacts with a metal, along with the evolution of hydrogen gas a salt is formed which has a negative ion composed of the metal and oxygen.

 

• When an acid reacts with a metal carbonate or metal hydrogencarbonate, it gives the corresponding salt, carbon dioxide gas and water.

 

• Acidic and basic solutions in water conduct electricity because they produce hydrogen and hydroxide ions respectively.

 

• The strength of an acid or an alkali can be tested by using a scale called the pH scale (0-14) which gives the measure of hydrogen ion concentration in a solution.

 

• A neutral solution has a pH of exactly 7, while an acidic solution has a pH less than 7 and a basic solution a pH more than 7.

 

• Living beings carry out their metabolic activities within an optimal pH range.

 

• Mixing concentrated acids or bases with water is a highly exothermic process.

 

• Acids and bases neutralise each other to form corresponding salts and water.

 

• Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt.

 

• Salts have various uses in everyday life and in industries.

3. Metals And Non-Metals

• Elements can be classified as metals and non-metals.

 

• Metals are lustrous, malleable, ductile and are good conductors of heat and electricity. They are solids at room temperature, except mercury which is a liquid.

 

• Metals can form positive ions by losing electrons to non-metals.

 

• Metals combine with oxygen to form basic oxides. Aluminium oxide and zinc oxide show the properties of both basic as well as acidic oxides. These oxides are known as amphoteric oxides.

 

• Different metals have different reactivities with water and dilute acids.

 

• A list of common metals arranged in order of their decreasing reactivity is known as an activity series.

 

• Metals above hydrogen in the Activity series can displace hydrogen from dilute acids.

 

• A more reactive metal displaces a less reactive metal from its salt solution.

 

• Metals occur in nature as free elements or in the form of their compounds.

 

• The extraction of metals from their ores and then refining them for use is known as metallurgy.

 

• An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal.

 

• The surface of some metals, such as iron, is corroded when they are exposed to moist air for a long period of time. This phenomenon is known as corrosion.

 

• Non-metals have properties opposite to that of metals. They are neither malleable nor ductile. They are bad conductors of heat and electricity, except for graphite, which conducts electricity.

 

• Non-metals form negatively charged ions by gaining electrons when reacting with metals.

 

• Non-metals form oxides which are either acidic or neutral.

 

• Non-metals do not displace hydrogen from dilute acids. They react with hydrogen to form hydrides.

4. Carbon and Its Compounds

Carbon is a versatile element that forms the basis for all living organisms and many of the things we use.

 

• This large variety of compounds is formed by carbon because of its tetravalency and the property of catenation that it exhibits.

 

• Covalent bonds are formed by the sharing of electrons between two atoms so that both can achieve a completely filled outermost shell.

 

• Carbon forms covalent bonds with itself and other elements such as hydrogen, oxygen, sulphur, nitrogen and chlorine.

 

• Carbon also forms compounds containing double and triple bonds between carbon atoms. These carbon chains may be in the form of straight chains, branched chains or rings.

 

• The ability of carbon to form chains gives rise to a homologous series of compounds in which the same functional group is attached to carbon chains of different lengths.

 

• The functional groups such as alcohols, aldehydes, ketones and carboxylic acids bestow characteristic properties to the carbon compounds that contain them.

 

• Carbon and its compounds are some of our major sources of fuels.

 

• Ethanol and ethanoic acid are carbon compounds of importance in our daily lives.

 

• The action of soaps and detergents is based on the presence of both hydrophobic and hydrophilic groups in the molecule and this helps to emulsify the oily dirt and hence its removal.

5. Periodic Classification of Elements
   

• Elements are classified on the basis of similarities in their properties.

 

• Döbereiner grouped the elements into triads and Newlands gave the Law of Octaves.

 

• Mendeléev arranged the elements in increasing order of their atomic masses and according to their chemical properties.

 

• Mendeléev even predicted the existence of some yet to be discovered elements on the basis of gaps in his Periodic Table.

 

• Anomalies in arrangement of elements based on increasing atomic mass could be removed when the elements were arranged in order of increasing atomic number, a fundamental property of the element discovered by Moseley.

 

• Elements in the Modern Periodic Table are arranged in 18 vertical columns called groups and 7 horizontal rows called periods.

 

• Elements thus arranged show periodicity of properties including atomic size, valency or combining capacity and metallic and non-metallic character.

12. Electricity

Learning points

Electric current and circuit

Electric Potential and Potential Difference

Circuit Diagram

Ohm's Law

Factors on which the resistance of a conductor depends

Resistance of a system of resistors

Resistors in series

Resistors in parallel

Heating effect of electric current

Practical Applications of heating effect of electric current

Electric Power

Questions Answers

NCERT Textbook.

1. What does an electric circuit mean?

Answer

An electric circuit is pathway in which current can follow. A circuit has electric devices, switching devices, source of energy etcetera. These are connected by conducting wire.

2. Define the unit of current.

Answer

When 1C of charge flows through a conductor in 1 s, it is called 1 ampere(A) current.

I = Q/t

The unit of electric current is ampere (A).

3. Calculate the number of electrons constituting one coulomb of charge.

Answer

We know that one electron possesses 1.6×10–¹⁹ C.

Therefore, 

Number of electron  = Total charge/Charge on 1 electron

or, No. of electron = 1/1.6×10–¹⁹

or, No. of electron = 6.25×10¹⁸ electrons. Ans.

1. Name a device that helps to maintain a potential difference across a conductor.

Answer

A cell, battery, power supply, etc helps to maintain potential difference across a conductor. 

2. What is meant by saying that the potential difference between two points is 1 V?

Answer 

When 1 J of work is required to move a charge of 1 C from one point to another, then it is said that the potential difference between two points is 1 V.

V = W/Q

or, 1 V = 1J/1C

3. How much energy is given to each coulomb of charge passing through a 6 V battery?

Answer 

From question it is clear that 

Work done = ?

Potential difference = 6 V

Charge = 1C.

We know that 

Potential difference = Work done/Charge

Therefore, 

Work done = Potential difference × Charge

or, Work done = 6 V×1C = 6 Joules Ans.

4. Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combination would be

(a) 1:2 

(b) 2:1

(c) 1:4

(d) 4:1

Answer

According to combination of resistance we know that

In the case of series

R(ES) = R1 + R2

From question it is clear that

R1 = R2 = R

R(S) = 2R

Similarly,

In the case of parallel

1/R(P) = 1/R1 + 1/R2

1/R(P) = 1/R + 1/R

R(P) = R/2

For same potential difference V,

We know that

V = IR

I = V/R

I(S) = V/R(S) = V/2R

Similarly,

I(P) = V/R(P) = 2V/R

H = I^2RT

Here,

I = Current follow through the conductor

R = Resistance

T = Time

Therefore,

H(S) = (V/2R)^2.R.T = V^2T/4R  ------- (i)

Similarly,

H(P) = (2V/R)^2 . R.T = 4V^2T/R ------- (ii)

Now, from (i) and (ii)

Therefore, ratio of heat produced in series and parallel

H(S)/H(P) = 1:4 Ans.

Continues 

Answers of the rest questions.....

11. The Human Eye and the Colourful World

The ability of the eye to focus on both near and distant objects, by adjusting its focal length, is called the accommodation of the eye.

The smallest distance, at which the eye can see objects clearly without strain, is called the point of the eye or the least distance of distinct vision. For a young adult with noumal vision, it is about 25 cm.

The common refractiove defects of vision include myopia, hypermetropia and presbyopia. Myopia (short - sightedness - the image of distant objects is focussed before the retina) is corrected by using a concave lens of suitable power. Hypermetropia (far - sightedness - the image of nearby objects is focussed beyond the retina) is corrected by using a convex lens of suitable poser. The eye loses its power of accommodation at old age.

The splitting of white light into its component colours is called dispersion.

Scattering of light causes the blue colour of sky and the reddening of the Sun at sunrise and sunset.

In this chapter, we shall use these ideas to study some of the optical phenomena in nature. We shall also discuss about rainbow for mation, splitting of white light and blue colour of the sky.

Questions and Answers of NCERT Textbook. 

Learning points

The Human eye.

Power of Accommodation.

Defects of Vision and their correction.

Refraction of light through a prism.

Dispersion of white light by a glass prism.

Atmospheric Refraction.

Scattering of Light

Q.No.1

What is mehant by power of accomodation of the eye ?

Answer

To see the near by object clearly, the ciliary muscles contact making the eye lens thicker. Thus, the focal length of the eye lense decreases and nearby objects become visible to the eye. Similarly, to see the far objects clearly, the ciliary muscles contact making the eye lens thinner. Thus, the focal length of the eye lens increases and far objects become visible to the eyes.

Hence, the human eye lens is able to adjust its focal length to view both nearby and far objects on the retina. This ability is called the power of accommodation of the eyes.

Q.No.2.

A person with a myopic eye cannon see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore power vision?

Answer 

The person is able to see nearby objects clearly, but he or she unable to see objects beyond 1.2 m. This happens because the image of an object beyond 1.2 m is formed in the front of the retina and not at the retina.

To correct this defect of vision, he must use a concave lens. The concave lens will bring the image back to the retina.

Q.No.3.

What is the far point and near point of the human eye with normal vision?

Answer 

For normal eyes, the least distance of distinct vision is 25 cm whereas far distance of distinct vision is infinite. 

Q.No. 4.

A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?

Answer 

Last row it means that distant objects. Student is unable to see distant objects clearly. He is suffering from myopia or far sightedness. This defect can be corrected by using concave lens.

1. The human eye can focus on objects at different distances by adjusting the focal length of the eye lens. This is due to

(a) presbyopia.

(b) accommodation.

(c) near-sightedness.

(d) far-sightedness.

Answer 

This is possible due to the power of accommodation of the eye lens. 

The correct option will be (b)

2. The human eye forms the image of an object at its

(a) cornea. (b) iris. (c) pupil. (d) retina.

Answer 

The human eye forms the image of an object at its retina. 

The correct option will be (d)

3. The least distance of distinct vision for a young adult with normal vision is about

(a) 25 m. (b) 2.5 cm. (c) 25 cm. (d) 2.5 m.

Answer 

The least distance of distinct vision for a young adult with normal vision is about 25 cm.

The correct option will be (c)

4. The change in focal length of an eye lens is caused by the action of the

(a) pupil. (b) retina. (c) ciliary muscles. (d) iris.

Answer 

The change in focal length of an eye lens is caused by the action of the ciliary muscles. 

5. A person needs a lens of power –5.5 dioptres for correcting his distant vision. For correcting his near vision he needs a lens of power +1.5 dioptre. What is the focal length of the lens required for correcting (i) distant vision, and (ii) near vision?

Answer 

From question it is clear that 

P = -5.5 D for distant vision. 

We know that 

P = 1/f

f = 1/P

Now putting the value of P.

f = 1/-5.5 = -0.181 m = -18.1 cm.

P = +1.5 for near vision. 

Similarly, 

f = 1/P 

f = 1/1.5 = 0.667 m = 66.7 cm.

6. The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?

Answer

From question it is clear that

Object distance = u = infinity 

Image distance = v = -80 cm

Focal length = f = ?

According to lens formula,  We know that

1/v - 1/u = 1/f

Now, putting the value of u, v and f.

-1/80 - 1/infinity  = 1/f

or, -1/80 = 1/f

f = -80 cm = -0.8 m

Power of lens = P = 1/f 

or, P = -1/0.8

P = -1.25 D. 

Therefore,  A concave lens of power -1.25 is required by the person to correct this defect. 

7. Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 25 cm.

Answer

A person suffering from hypermetropia can see the distant objects clearly but faces difficulty in seeing nearby by objects clearly. This defect of vision is corrected by using a convex lens. A convex lens of suitable power converges the incoming light in such a way that the image is formed on the retina, as shown in the above figure.

The convex lens actually creates a virtual image of a nearby objects (N' in the figure) at the near point of vision (N) of the person suffering from hypermetropia. 

The given person will be able to clearly see the object kept at 25 cm (least distance of distinct vision), if the image of the the object is formed at his near point, which is given as 1 m.

Object distance = u = -25 cm

Image distance = v = -1 m = -100 cm.

Focal length = f ?

According to lens formula 

We know that 

1/v - 1/u = 1/f

-1/100 - 1/-25 = 1/f

or, -1/100 + 1/25 = 1/f

Therefore,  f = 100/3 cm = 1/3 m.

We know that 

P = 1/f

P = 3 D 

A convex lens of power +3 D is required to correct the defect. 

8. Why is a normal eye not able to see clearly the objects placed closer than 25 cm?

Answer

The least distance of distinct vision of a normal eye is 25 cm. Therefore, a normal not able to see clearly the objects placed closer than 25 cm.

9. What happens to the image distance in the eye when we increase the distance of an object from the eye ?

Answer

Since the size of eyes cannot increase or decrease, the image distance remains constant. When we increase the distance of an object from the eye, the image distance in the eye does not change. The increase in the object distance is compensated by the change in the focal length of the eye lens. The focal length of the eyes changes in such a way that the image is always formed at the retina of the eye.

10. Why do stars twinkle ?

Answer

Stars emit their own light and they twinkle due to the atmospheric refraction of light. Stars are very far away from the earth. Hence, they are considered as point sources of light. When the light coming from stars enters the earth’s atmosphere, it gets refracted at different levels because of the variation in the air density at different levels of theatmosphere. When the star light refracted by the atmosphere comes more towards us, it appears brighter than when it comes less towards us. Therefore, it appears as if the stars are twinkling at night.

11. Explain why the planets do not twinkle? 

Answer 

Planets do not twinkle because they appear larger in size than the stars as they are relatively closer to earth. Planets can be considered as a collection of a large number of point-size sources of light. The different parts of these planets produce either brighter or dimmer effect in such a way that the average of brighter and dimmer effect is zero. Hence, the twinkling effects of the planets are nullified and they do not twinkle.

12.Why does the Sun appear reddish early in the morning? 

Answer

During sunrise, the light rays coming from the Sun have to travel a greater distance in the earth’s atmosphere before reaching our eyes. In this journey, the shorter wavelengths of lights are scattered out and only longer wavelengths are able to reach our eyes. Since blue colour has a shorter wavelength and red colour has a longer wavelength, the red colour is able to reach our eyes after the atmospheric scattering of light. Therefore, the Sun appears reddish early in the morning.

13.Why does the sky appear dark instead of blue to an astronaut? 

Answer

The sky appears dark instead of blue to an astronaut because there is no atmosphere in the outer space that can scatter the sunlight. As the sunlight is not scattered, no scattered light reach the eyes of the astronauts and the sky appears black to them.