Sound needs a medium for propagation. Take a metal or glass tumbler. Place a cellphone in it. Ask your friend to give a ring on this cellphone. Listen to the ring carefully. Now surround the rim of the tumbler with your hands. Suck all the air of the tumbler. Once again make a ring in cellphone. Sound will completely stop because air has been removed completely from the vessel and forms vacuum. Hence sound needs a medium for propagation.

On being struck by lightning, victim carries no electrical charge. The death by lightning occurs due to cardiac arrest and stopped breathing. We can give first aid by performing CPR and mouth to mouth breathing.

Animals whose numbers are diminishing to level that they might face extinction are known as the endangered animals e.g., Dinosaurs became extinct a long time ago.

Characteristics of an ideal fuel:
(i) It is readily available, cheap and can easily be transported.
(ii) It burns easily, has higher calorific value and does not leave behind any undesirable substances.

Under unfavourable conditions of temperature and water, they generally form a hard and tough covering called cyst. This protects them. When favourable conditions come, they emerge from their shell, multiply and go through their life cycle.

Plastic is a polymer like the synthetic fibre.

Microorganisms (pathogens) such as viruses are included in biological water pollutants.

During the electrolysis of water, hydrogen gas is evolved at the cathode.

When an object moves in a fluid, then the resistance to the movement of object exerted by fluid is called fluid friction.

Yes, nearly everything we see around us due to reflected light, e.q. moon receives light from the sun and reflects it.

The planet which is known to have a largest number of satellites is Jupiter.

It is the force of gravity which is responsible for the grains to fall down. 

This period of Changes, i.e adolescence begins around the age of 11 and lasts upto 18 or 19 years.

Metamorphosis is the term used for the change from tadpole to frog.

Amoeba is a cell that behaves like a complete organism.

Metals produce ringing sound, so they are called sonorous.

The process of transferring the seedings from the nursery to the main field by hand or manually is called seed transplantation.

Different phases of moon are visible from the Earth. This change in shapes occurs due to variation in sunlight reflected by moon from its surface. At certain times, it appears to be bright whereas at others it appears to be dark. When brightness of moon is increasing, it is called waxing, when brightness of moon is decreasing, it is called vanning.

(i) Yes, there is a difference because bird lays eggs from which its young ones hatch out whereas human gives birth to a baby directly.
(ii) Hen, frog, snake and lizards are few animals that lay eggs.
(iii) Sumitra is observant, intelligent and curious.

These days the head of the match sticks contains only antimony trisulphide and potassium chlorate. The rubbing surface has powdered glass and a little red phosphorus. When the match stick is struck against the rubbing surface i.e., some red phosphorus, this immediately reacts with potassium chlorate on the match stick head to produce enough heat to ignite antimony trisulphide and start combustion.

Plastic is very strong, light and durable. It can be moulded into different shapes and sizes. It is used for various purposes. Plastics are generally cheaper than metals. They are widely used in industry and for household articles.

Two sources which cause air pollution due to SPM are as follows :
(i) Automobiles which burn diesel and petrol, produce SPMthat remain suspended in air and reduce visibility. When inhaled, they cause diseases.
(ii) Industrial activities like manufacturing of steel and mining give out SPM which also pollute the atmosphere.

Due to the heating effect of current, the filament of the bulb gets heated to a high temperature and it starts glowing. However, if the current through a circuit is too weak, the filament does not get heated sufficiently and it does not glow.

Friction as a friend
(i) It allows us to walk comfortably.
(ii) It allows us to minimise the speed or to stop the moving objects.
(iii) It allows us to write on a board with chalk.
Friction as a foe
(i) It causes wear and tear in objects.
(ii) It causes damage to the parts of machines.
(iii) It does not allow the free movement of objects.

Differences between regular and diffused reflection are

No, the diffused reflection does not mean the failure of the laws of reflection.

As, it is clear from the diagram whether we bring a positive or negative rod, the strips will repel always because equal amount of charges are transferred to the strips and like charges always repel each other.

Since, there are many actions which give us the feeling of force like we hit or catch many objects in our regular routine. Most of the times, we see that the moving ball stops after sometime and it changes the direction of motion when it is hit by a bat also, when we compress a spring, its shape and size changes.

The cell number in an organism varies with the size of organism. Thus, smaller organisms have limited number of cells. while the larger ones (such as elephant, whale or banyan tree) have a countless number of cells. In man, the number of cells is estimated to be about 100 trillion (10¹⁴).

Adolescence is the period of life, in which organisms become reproductively active. In other words, it is the period of attaining reproductive maturity in boys and girls, which starts from 11-13 years and lasts upto 18-19 years in humans.

If we go on cutting trees, then
(i) many animals will loose their shelters.
(ii) there would be scarcity of materials like fruits, paper, which we get from forests.
(iii) flood and drought will become more frequent.
(iv) earth will loose its most fertile layer and transform into desert.

Metals react with acids to produce salt and hydrogen gas which burns with a 'pop' sound. Non-metals do not react with acids. Copper does not react with dilute hydrochloric acid and dilute sulphuric acid but it reacts with hot and concentrated sulphuric acid, but no hydrogen gas is produced.

Oil is lighter than water, hence floats over it.

Microorganisms survive under adverse conditions by forming a hard and protective covering called cyst around them. On return of favourable conditions, the cyst wall breaks and microorganisms resume their life cycles.

(a) Fertiliser
(b) Crop
(c) Ploughing or Tilling
(d) Pisciculture

Air gets polluted by many reasons. Few of them are as follow:
(i) Vehicles produce high level of pollutants like carbon monoxide, carbon dioxide, nitrogen oxide, smoke etc. These are very poisonous gases. Burning of fuel from vehicles also produces pollution.
(ii) Many industries are also responsible for causing air pollution. Petroleum refineries release polluted gases such as sulphur dioxide, nitrogen dioxide etc. They cause respiratory problems, including lung damage.
(iii)Other kinds of pollutants are CFCs which are largely used in refrigerators, air conditioners and aerosol sprays. Those protect us from ultraviolet rays of the Sun.
(iv) Some human activities like forest fire, burning of fire wood, cow dung cakes, burning of chaff etc. cause air pollution.
(v) Some natural phenomenon like fast dust storms, volcanic eruption produce smoke and dust particles

Forces can be of two types:
(i) Contact forces.
(ii) Non-contact forces.
(i) Contact forces : The forces that come into play when two objects come in contact with each other.
(a) Muscular force: The force which is exerted due to action of muscles is known as the muscular force. e.g., running, bending, walking etc.
(b) Frictional Force: The force responsible for changing the state of motion of an object. Equal and opposite forces are being exerted on an object when its surface comes in contact with other surface. e.g., a car or scooter comes to rest.
(ii) Non-contact forces: The forces that can be exerted from a distance without establishing a contact are called the non-contact forces.
(a) Magnetic forces : Force exerted by a magnet on another magnet or magnetic substances like iron is called magnetic force. e.g., Car sticking to an electromagnet.
(b) Electrostatic force : Force exerted by a charged body on another charged body or uncharged body is called electrostatic force. e.g., If we rub a comb with hair and bring it near some small bits of paper it attracts the bits of paper towards itself. This is electrostatic force.
(c) Force of gravity : The earth pulls every object towards its centre. The force exerted by the earth is called the force of gravity.

Gene is a unit of inheritance in living organism. It controls the transfer of hereditary characteristics from parents to offsprings.
This means that your parents pass some of their characteristics to you. If your father has brown eyes, you may have brown eyes. However, the different combination of genes from parents results in different characteristics.

1. Seismograph,
2. Richter,
3. Earthquake,
4. Conduction.

When an animal is killed illegally, it is called poaching. It usually occurs when an animal possesses something that is considered valuable.
Effect of Poaching on environment : The whole ecosystem is affected due to harm caused on animal population. Everything from the animals to the plants and even the people in a specific place is negatively affected. We need various species of flora and fauna in our environmental ecosystem so that it is balanced and healthy. Our own survival depends on it.
Effect of Poaching on humans : Two serious problems are faced by humans, first is spread of food-borne illnesses e.g., Ebola and anthrax and second major affect is depletion of natural resources.

The wasting of iron objects due to rusting causes a big loss to the country's economy, so it must be prevent by following methods:
(i) By painting : Paint is applied to the surface of an iron object, then air and moisture cannot come in contact of iron and hence no rusting occurs.
(ii) By applying grease or oil : Tools and machine parts made of iron and steel are smeared with grease or oil to prevent their rusting.
(iii) By galvanization : Galvanization is done by dipping an iron object in molten zinc metal. This thin layer of zinc metal on the surface of iron objects protects them from rusting.
(iv) By tin plating and chromium-plating : When a thin layer of tin metal is deposited on iron and steel objects by electroplating then the iron and steel objects are protected from rusting.
(v) By alloying it to make stainless steel: When iron is alloyed with chromium and nickel, stainless steel is obtained, which does not rust at all

The supply of water to crops at different intervals is called irrigation. Various systems of irrigation are:
(i) Traditional methods: The water available in wells, lakes and canals is lifted up by
(a) Moat (Pulley system);
(b) Chain pump
(c) Dhekli and;
(d) Rahat (Lever system)
Pumps are commonly used for lifting water.
(ii) Modern methods:
(a) Sprinkler system: This system is more useful on uneven land. The perpendicular pipes, having rotating nozzles on top, are jointed to the main pipeline at regular intervals. When water flows through main pipes, it gets sprinkled on the crop as if it is raining.
(b) Drip system: In this system water falls drop by drop just at the position of the roots. It is the best technique for watering fruit plants, garden and trees

Take the tray from the inside of a discarded matchbox. Wrap an electric wire a few times around the tray. Place a small compass needle inside it. Now connect one free end of the wire to the one terminal of a battery. Leave the other end free.
Take another piece of wire and connect it to the other terminal of the battery. Join the free ends of two wires momentarily. The compass needle should show deflection. Your tester with two free ends of the wire is ready.

(a) Since, the player rub his hand due to which the palms become warm which absorb the moisture from the surface and make the surface rough. So, due to roughness of hands, the ball may get a better grip between the hands and does not slip.
(b) Since, the player makes the palm surface oily. So, the number of irregularities decreases and the surface becomes smooth. So, the ball slips off easily from the hand.
(c) As, teacher wants to teach the students through easy example. So, this act of teacher shows the experience and ideality of teacher.

The correct diagrams are as below:

(a) The dotted line represents the height of boys.
(b) The solid line represents the height of girls.
(c) At the on-set of puberty, girls grow faster in height than the boys and by the age of 18 years, approximately both reach their maximum height.
(d) No, the rate of growth in height varies among individuals. Some may grow in height suddenly at puberty and then slow down, while others may grow gradually.

The tail of the comet is always directed away from the Sun. The tail will be longest in the position B because the tail is visible only when the comet passes through the inner solar system and B is nearest.

(a) The parts in the figure are labelled below:

(b) The embryo continues to develop after it gets embedded in the uterus. It divides and differentiates into three germ layers which give rise to different body parts such as hands, legs, head, eyes, ears, etc. This stage where all the body parts are distinct and easily identified in developing embryo is called foetus. After completion of development of foetus, mother gives birth to baby.

Sound is produced when any object starts vibrating by any means. These vibrations travel from the source all around the environment through the particles of the environment, thus, it reaches to its destination, i.e. our ear. Now, it enters our ear and travels down a canal at the end of which a thin membrane is stretched tightly known as eardrum. The eardrum sends vibrations to inner part of the ear and finally reaches to the brain and we hear the sounds.

Reasons of forest fires are
(i) At high temperature, sometimes dry grass catches fire which spreads throughout the forest.
(ii) Campfire may also be a reason.
(iii) Lightning.
(iv) The use of fires by villagers to ward off wild animals.
(v) Fire lit intentionally by people living around forests for recreation.
(vi) Fires started accidentally by careless visitors to forests how discard cigarette butts.
(vii) The friction of bamboos due to high wind velocity and rolling stones.

The natural resources which are present in a limited quantity in nature and can be exhausted (used up) by human activities are called exhaustible natural resources, e.g. coal, petroleum, natural gas, minerals, forests, wildlife, etc.
It requires millions of years for the conversion of the dead organisms into petroleum, from which petrol is separated. So, once the present stock of it gets exhausted, no new supplies of it will be available to us in the near future, whereas sunlight is present in an unlimited quantity in nature, so it is inexhaustible natural resource. It is not likely to be exhausted by human activities.

(a) Sometimes, the animals (like cow) eat up the polythene bags and wrappers of food along with the left-over food thrown on garbage dumps.
(b) To deelop habits which are environment friendly one should follow 4 R principle which stands for reduce, reuse, recycle and recover.
(c) Karan followed his mother's advice, it shows that he is an intelligent, obedient caring and responsible boy

(a) Organisms that cannot be seen with eyes alone are called microbes.
(b) Microbes are useful to humans in many ways. They help in the production of curd, cheese, in cleaning the environment, etc.
(c) (i) Lactobacillus bacteria.
(ii) Penicillium
(d) Diseases caused by microbes are polio, malaria, etc.
(e) Jasmine is attentive, intelligent and curious.