Lecture-2 : CLASS-X: SCIENCE : Chapter: Electricity Content: numericals

NUMERICAL PROBLEMS ON ELECTRICITY; CLASS 10

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Q1. How much work is done in moving a charge of 3 coulombs from a point at 110 volts to a point at 220 volts?

Soln. We know, 

Potential difference = work done/charge moved

or.          V   =   W/Q

∴   W =  VQ

Here, potential difference, V = 220 - 110 = 110 volts and Charge moved , Q = 3 coulombs

 ∴  W = VQ = 3 x 110 joules = 330 joules

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Q2. How much energy is given to each coulomb of charge passing through a 6 volt battery?

Soln. We know, 

Potential difference = work done/charge moved

or.          V   =   W/Q

∴   W =  VQ

Here, potential difference, V = 6 volts

and charge Q = 1 coulomb ( each coulomb given)

∴   W =  VQ = 6 x 1 joules = 6 joules

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Q3. What is the potential difference between the terminals of a battery if 500 joules of work is required to transfer 25 coulombs of charge from one terminal of battery to the other?

Soln. We know, 

Potential difference = work done/charge moved

or.          V   =   W/Q

Workdone , W = 500 joules

Charge moved, Q = 25 coulombs

∴  V   =   W/Q = 500/25 = 20 volts

Therefore, the potential difference between the terminals of the battery = 20 volts

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Q4. A circuit contains a battery of 1.4 V with a resistance of 2 ohms and a resistance of 5 ohms connected in series. Calculate the current flowing through the circuit and the potential difference across the 5 ohm resistance.

Using Ohm's law, we can calculate the current flowing through the circuit as:

I = V / R_total

where V is the voltage of the battery, and R_total is the total resistance of the circuit, which is the sum of the resistance of the 2-ohm resistor and the 5-ohm resistor:

R_total = R₁ + R₂ = 2 ohms + 5 ohms = 7 ohms

So we have:

I = 1.4 V / 7 ohms = 0.2 A

Therefore, the current flowing through the circuit is 0.2 A.

To calculate the potential difference across the 5 ohm resistor, we can use Ohm's law again, using the current we just calculated:

V_5ohm = I * R₂

where R₂ is the resistance of the 5 ohm resistor. Substituting the values we have:

V_5ohm = 0.2 A * 5 ohms = 1 V

Therefore, the potential difference across the 5 ohm resistor is 1 V.

Q5. A parallel circuit contains two resistors, one with a resistance of 10 ohms and the other with a resistance of 20 ohms. If the voltage across the circuit is 12 volts, calculate the total current flowing through the circuit and the current through each resistor.

Q6. An electric motor is rated at 120 volts and draws a current of 5 amperes. Calculate the power consumed by the motor.

Q7. A 220-volt electric heater draws a current of 5 amperes. Calculate the resistance of the heater.

Q8. A circuit contains a 10-ohm resistor, a 5-ohm resistor, and a 12-volt battery. Calculate the total current flowing through the circuit and the potential difference across each resistor.

Q9. An electric power station produces 1000 megawatts of power. If the voltage of the power lines is 100,000 volts, calculate the current flowing through the lines.

Q10. A transformer has a primary coil of 100 turns and a secondary coil of 500 turns. If the primary coil is connected to a 240-volt power source, calculate the voltage across the secondary coil.

Lecture-1 : CLASS-X: SCIENCE : Chapter: Electricity

Class X  |   Science  |  Electricity

             notes prepared by Subhankar Karmakar

CHARGE: 

Charge is a inherent property of a matter.

Types of Electric Charges:

There are two types of electric charges. 

1. Positive Charge

2. Negative Charge

POSITIVE CHARGE:

The charge acquired by a glass rod (rubbed with a silk cloth) is called positive charge.

NEGATIVE CHARGE:  

The charge acquired by an ebonite rod (rubbed with a wooden clock) is called negative charge

Property of electric charge:

1. Opposite charges or unlike charges attract each other

2. Similar charges or like charges repel each other

The SI unit of electric charge:

The SI unit of electric charge is called Coulomb.

It is denoted by the symbol C. 

1 coulomb charge:

1 coulomb charge is that charge which exerts a force of 9 x 10⁹ N force on an equal charge placed at a distance of 1  m from it.

Proton, Electron and their charge:

By convention, it is taken that electrons are negative charges where as protons are positive charges

Magnitude of a proton and an electron charge is equal to 1.6x10⁻¹⁹ C

Number of electrons in 1 coulomb charge:

Suppose we want to to find out how many  electrons will make 1 C

Formula: 

If q = magnitude of charge

   n = number of of electrons

   e = charge of an electron 

      = 1.6 x 10⁻¹⁹ C

then 

     q = ne

therefore, n = q/e

                      = 1/1.6 x 10⁻¹⁹

                      = 6.25 x 10¹⁸

So, 6.25 x 10¹⁸ electrons together make 1 coulomb charge

Conductors: 

Those substances through which electricity can flow are called conductors. All the metals are conductors. Therefore, copper, silver, aluminium, gold, iron etc are all good conductors. One non metal graphite are also conductor. 

Insulators: 

Those substances through which electricity cannot flow are called insulators. All the nonmetals are  insulators. Glass, ebonite, rubber, most plastics, paper, drywood, cotton, Mica, bakelite, porcelain and dry air examples of insulators. 

Reason behind the flow of electricity through a substance:

Electricity or electric charge can flow through a substance if the substance contains free electron. The electrons which can move from one atom to another atom freely  are called free electron.

Therefore, all the conductors contain free electrons where as all the insulators do not contain any free electron.

Free Electron: The electrons which can easily move from atom to atom are called free electron. They are the the carriers of electricity.

Electric potential: (V)

The electric potential or potential at a point in an electric field is defined as the work done in moving a unit positive charge from infinity to that point.

Explanation: suppose you take an unit positive charge and place it very very large distance which is called infinite distance, from that point if you want to bring/ move the charge against an electric field to a point you have to do a work done, that work done will be called electric potential.

Electric potential is denoted by symbol V.

SI unit of electric potential is called volt. Symbol is V. 

Definition of 1 volt: 

A potential of 1 volt at a point inside an electric field means that 1 Joule of work is done in moving one coulomb of positive charge from infinity to that point.

Electric potential difference or potential difference:

The difference in electric potential between two points is known as potential difference between that two points.

Definition: 

The potential difference between two points in an electric circuit is defined as the amount of work ok done in moving a unit charge from one point to the other point.

Formula:

Potential difference = (workdone)/quantity of charge moved

If W = work done

    Q = quantity of charge moved

    V = potential difference between two points

then, V = W/Q

SI unit of potential difference is also volt (V)

1 Volt potential difference means it needs 1 joule of work to move 1 coulomb electric charge from one point to the other.

1 volt = 1 joule / 1 coulomb

1 V = 1 J/C = 1 JC⁻¹

Voltmeter: 

The instrument by which electric potential difference can be measured is called voltmeter. Voltmeter has high resistance, and it allows only very small current through it. Potential difference is also known by voltage.

Lecture 7: CLASS VIII: SCIENCE: CHAPTER 2: CLASSIFICATION OF MICRO-ORGANISMS

Class VIII: SCIENCE:

                       Notes prepared by Subhankar Karmakar

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Micro-organisms: some of them are bad, but some of them are good too.

Those organisms which are too small to be seen without a microscope are called micro-organisms. Some of the microorganisms are useful to us, but some of the micro-organisms are harmful to us. 

Good micro-organisms:

For example, the microorganisms by certain bacteria help in making food products such as curd and cheese. Microorganisms are are also useful in making bread, cakes, pastries, alcohol, acetic acid or vinegar and medicines called antibiotics. 

Bad Micro-organisms;

On the other hand, the microorganisms like certain bacteria and fungi make our food rotten. The Microorganisms also caused diseases in humans, other animals and plants. The diseases like common cold, malaria, skin infections, typhoid, tuberculosis, tetanus, cholera, measles, chicken pox, smallpox, AIDS and of course covid-19 are all caused by the action of various types microorganisms.

Major groups of microorganisms:

Microorganisms are classified into 5 major groups. This groups are: 

1. Bacteria  

2. Viruses  

3. Protozoa

4. Fungi

5. Algae

Cellular structure of microorganisms: 

Some microorganisms are unicellular or single celled where as many microorganisms are multicellular or multi celled. 

1. Bacteria:

Bacteria are very small, single celled microorganisms which have cell walls but do not have an organised nucleus and other structures. They come in various shapes like spherical bacteria, rod shaped bacteria, and spiral bacteria. 

Example: Beneficial bacteria: 

Lactobacillus bacteria, which are useful for making foods like curd and Rhizobium bacteria which help in nitrogen fixation and decomposition of organic waste matter.

Harmful bacteria: Diseases like cholera, typhoid, tuberculosis or TB, diphtheria, whooping cough and food poisoning all are caused by actions of bacteria.

2. Viruses: 

Viruses are the smallest microorganisms which can develop only inside the cells of the host organisms. They are neither alive nor dead. They are not exactly living things.

Viruses can reproduce and multiply only inside the cells of other organisms like animal cells plant cells or bacteria cells.

Viruses are the agents of disease. The human diseases such as common cold, influenza, measles, polio, chicken pox, HIV, smallpox and covid-19 are all caused by viruses.

3. Protozoa: 

Protozoa are a group of single celled microorganisms which are classified as animals.

They are found in lakes, ponds, dirty water drains, sea water and damp soil. 

Some common examples of protozoa are:

Paramecium, Entamoeba and Plasmodium. 

Protozoa can be parasites also. 

Diseases caused by protozoa: 

• Entamoeba is a protozoan which causes a disease known as amoebic dysentery. 

• Plasmodium is a protozoan which causes a disease called malaria. Plasmodium is also known as Malarial Parasite.

4. Algae: 

Algae is a large group of simple plant like organisms. Like plants, they contain chlorophyll and produce food by photosynthesis.

Example:  Chlamydomonas, Spirogyra, blue green algae, Diatoms are example of algae.

Blue green algae have the ability to fix nitrogen gas of atmosphere.

5. Fungi:

Fungi are a  large group of organisms which do not have chlorophyll and do not photosynthesize. 

Some examples of fungi are: Yeast, Moulds like penicillium and aspergillus, mushrooms, toadstools, puffballs.

All fungi are made up of fine threads called hyphae except Yeast. 

Some of the human diseases caused by fungi are ringworm and athlete's foot. 

Lecture- 6: CLASS VIII : SCIENCE: CHAPTER- 1 : STORAGE

VIII-SCIENCE

Prepared By Subhankar Karmakar

7. STORAGE OF FOOD GRAINS

The fresh food grains (like wheat) obtained by the harvesting of crops contain more moisture than required for their safe storage. So, the food grains (like wheat) obtained by harvesting the crops are dried in the sunshine before storing, to reduce their moisture. It is necessary to reduce the moisture content of grains before storing to prevent their spoilage during storage.

 This is because the higher moisture content in food grains promotes the growth of fungus and mould on the stored grains which damages them (and makes them lose their germination capacity). 

The farmers store the dried food grains at home in metal bins (metal drums) and jute bags (called gunny bags). Dried neem leaves are used for storing food grains at home. For example, when wheat is stored at home in iron drums, then some dried been leaves are put on it. Dry been leaves protect the stored food grains from pests such as insects and micro-organisms. 

The large scale storage of food grains ( like wheat and rice) is done in two ways:

(a) in gunny bags, and

(b) in grain silos ( bulk storage of food grains)

FOOD FROM ANIMALS:

The food provided by animals consists of Milk, Eggs and Meat.

The animals which provide us food are mainly of two types:

(a) Milk yielding animals,

(b) Meat and Egg yielding animals.

Examples of milk yielding animals:

Cow, Buffalo and Goat

Examples of meat and egg yielding animals are: Goat, Sheep, Fish and Poultry.

ANIMAL HUSBANDRY:

The branch of agriculture which deals with the feeding, shelter, health and breeding of domestic animals is called animal husbandry.

The various practices necessary for raising animals for food and other purposes (or the elements of animal husbandry) are :

1. Proper feeding of animals,

2. Proper shelter for animals,

3. Prevention and cure of animal diseases, and

4. Proper breeding of animals.

FISH AS FOOD:

Fish is an important source of animal food. Many people living in the coastal areas (sea-side areas) consume fish as a major part of their diet. Fish is rich in proteins. It is a highly nutritious and easily digestible food. Fish liver oil is rich in vitamin A and vitamin D. For example, Cod liver oil (or Cod fish liver oil) is rich in vitamin A and vitamin D.

Lecture 5: CLASS VIII: SCIENCE: CHAPTER 1: HARVESTING

CLASS-VIII; SCIENCE

Prepared by Subhankar Karmakar

6. HARVESTING:

The cutting and gathering of the matured food crop is called harvesting. 

MANUAL HARVESTING:

In harvesting, the crops like wheat or rice are cut close to the ground by hand using a cutting tool called sickle and this is called manual harvesting.

MACHINE HARVESTING:

In large fields, wheat and paddy crops are cut by a motorised machine called harvester.

THRESHING:

After harvesting the crop, the grains are separated from the harvested crops. The process of beating out the grains from the harvested crops plants is called threshing. It can be done manually as well as with the help of a motorised machine called thresher.

WINNOWING: 

The process of threshing brings out grains from the cut and dried crop plants, but this grain is mixed with chaff ( outer inedible covering of grain) and hay. The process of separating grain from chaff and hay with the help of wind is called winnowing.

COMBINE: 

A combine is a large machine which cuts the standing cereal crop in the fields, threshes it, and separates the chaff from grain in one operation.

Lecture-4: CLASS VIII: SCIENCE: CHAPTER -1: WEEDS

CLASS-VIII; SCIENCE

Prepared by Subhankar Karmakar

5) REMOVING THE WEEDS OR WEEDING

Weeds: The unwanted plants or wild plants which grow along with a cultivated crop are called weeds. Like some of the common weeds found in wheat and rice fields are:

(a) Wild oat 

(b) Grass

(c) Amaranthus

(d) Chenopodium

HARMFUL EFFECTS OF WEEDS:

The growth of weeds in the fields is harmful because 

(i) they consume a lot of fertilisers, water, sunlight and space, meant for the crops plants, 

(ii) weeds reduce the crop yield and lower the quality of food grains,

(iii) some weeds are poisonous for human beings and animals,

(iv) some weeds interfere in harvesting.

WEEDING: 

The process of removing weeds from a crop field is called weeding. 

VARIOUS METHODS OF WEEDING:

(a) Removal of weeds by pulling them out with hand.

(b) Removal of weeds by using a trowel ( khurpa)

(c) Destroying the weeds by spraying special chemicals called weedicides.

WEEDICIDES: 

The poisonous chemicals which are used to kill weeds in the fields are called weedicides.  Some of the common weedicides are: 2,4-D, MCPA, Butachlor. 

Lecture 3: CLASS-VIII: SCIENCE: CHAPTER 1: MANURE & FERTILIZER

CLASS VIII   |    SCIENCE    |    CHAPTER 1

      Notes prepared by Subhankar Karmakar

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click to access other class notes

SCIENCE: CLASS VIII CBSE (CLASS NOTES)

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Lecture 3: 

ADDING MANURE AND FERTILISERS

1. NEED OF MANURE & FERTILISERS

Repeated growing of crops in the same field removes a lot of precious mineral elements, organic matter and other materials from the soil. The deficiency of plant nutrients and organic matter in the soil is made up by adding manures and fertilisers to the soil.

2. MANURES: 

Manure is a natural fertiliser. A manure is a natural substance obtained by the decomposition of animal wastes like cow-dung, human wastes and plant residues, which supplies essential elements and humus to the soil and makes it more fertile.

3. PREPARATION OF MANURES: 

Manures are prepared from animal wastes, human wastes and plant residues by the action of micro- organisms. In order to prepare manure, farmer dump animal wastes and plant wastes in pits at open places and allow it to decompose slowly. The decomposition is carried out by some micro-organisms. The decomposed animal and plant matter is used as organic manure.

4. FUNCTION OF MANURES:

Manures provide a lot of organic matter like humus to the soil. A manure improves the soil texture for better retention of water and aeration. 

5. CHEMICAL FERTILISERS:

A chemical fertiliser is a salt or an organic compound containing the necessary plant nutrients like nitrogen, phosphorus or potassium, to make the soil more fertile. A chemical fertiliser is rich in a particular plant nutrients such as nitrogen, phosphorus or potassium (NPK). Some examples of chemical fertilisers are Urea, Ammonium sulphate, Superphosphate, Potash and NPK.

6. DIFFERENCES BETWEEN MANURES AND FERTILISERS: 

1. A manure is a natural substance obtained by the decomposition of animal wastes like cow dung, human waste and plant residue. 

But a fertilizer is a salt or an organic compound.

2. Manure is not very rich in essential plant nutrients like nitrogen, phosphorus and potassium where as fertilizers are very rich in plant nutrients like nitrogen, phosphorus and potassium.

3. A manure provides a lot of organic matter like humus to the soil but a fertilizer does not provide any humus to the soil.

4. A manure is absorbed slowly by the plants because it is not much soluble in water but being soluble in water if fertilizer is readily absorbed by the plants.

5. Menure can be prepared in the field but fertilizers are prepared in factories.

7. ADVANTAGES OF MANURE:

Organic manure is considered better than Fertilisers because of the following reasons:

1. Manure enhances the water holding capacity of the soil.

2. Manure makes the soil porous due to which the exchange of gases becomes easy.

3. Manure increases the number of useful microbes in the soil.

4. Manure improves the texture of the soil.

8. LEGUMINOUS CROPS:

The pulses, peas, beans, groundnut, gram and clover are called leguminous crops. Leguminous crops have the ability to fix atmospheric nitrogen to form nitrogen compounds. The planting of leguminous crops in a field has the same effect as adding nitrogenous fertiliser in the field.

9. CROP ROTATION:

The practice in which different types of crops like leguminous crops and non-leguminous crops are grown in the same field or soil is called crop rotation. In crop rotation, cereal crops like Wheat, Maize, Paddy and Millet are grown alternately with leguminous crops pulses, peas, beans, groundnut and clover etc. in the same field.

10. ADVANTAGES OF CROP ROTATION:

Rotation of crops has the following advantages:

1. Rotation of crops improves the fertility of the soil and hence increases the production.

2. Rotation of crops saves a lot of nitrogenous fertiliser.

QUESTIONS BANK:

21. Why does soil needs manuring?

22. What are manures? Why it is needed?

23. What are the advantages of manures?

24. What are chemical fertilisers? Give examples.

25. Differentiate between manures and fertilisers.

26. What are leguminous plants? What they are being planted in the field?

27. What are crop rotation? What are their advantages?