FORESTS:OUR LIFE LINE

 NOTES

Deforestation

Clearing of forests and trees eventually using that land for other purposes like agriculture and other human activities. The main causes for deforestation are:
(i) agricultural expansion
(ii) livestock grazing
(iii) Illegal logging, which is cutting, processing of trees in prohibited land.
(iv) human infrastructure expansion
(v) overpopulation

Species

Species is a group of populations, which are capable of interbreeding (reproducing fertile offspring).

Flora and fauna

The plants and animals observed in a specific region are referred to as flora and fauna of that region.

Extinction

Extinction

• Extinction is the dying out or death of all members of a species.
• Human intervention (either directly or indirectly) has become the leading cause of species extinction.
• Eg: Animals like the Dodo bird, Tasmanian wolf are extinct.

To know more about Extinction, visit here.

Tiger Project

Endangered animals
Animals whose count is reducing to an extent that they might face extinction are known as the endangered animals. Eg: Giant panda, tiger. Red Data Book is a source(reference) book, keeping a record of all the plant and animals that are endangered.
Ecosystem
Ecosystem is the region consisting of all the living plants, animals and microorganisms in an area along with non-living components such as climate, soil, river deltas, etc.

Migration

Migration
Migration is defined as the movement of organisms in large numbers from one place to another.

Exercise Questions

1. Explain how animals dwelling in the forest help it grow and regenerate.

Solution:

Animals dwelling in the forest help it grow and regenerate in the following ways

• Animals help in dispersing plant seeds.
• Decaying animal dung provides nutrients for plants to grow
• Microorganisms convert the dead plants and animals to humus

2. Explain how forests prevent floods.

Solution:

Plants in the forests will not allow the rainwater to fall directly on earth and these plants also hold water which helps in preventing floods.

3. What are decomposers? Name any two of them. What do they do in the forest?

Solution:

The micro-organisms which convert the dead plants and animals to humus are known as decomposers. Example: bacteria and fungi. They help in recycling of nutrients by decomposing dead plants and animals.

4. Explain the role of forest in maintaining the balance between oxygen and carbon dioxide in the atmosphere.

Solution:

Plants in the forests consume carbon dioxide and release oxygen by photosynthesis process. This helps in balancing oxygen and carbon dioxide in the atmosphere.

5. Explain why there is no waste in a forest.

Solution:

There is no waste in a forest because waste created is bio-degradable, which gets converted to humus by the action of microorganism.

6. List five products we get from forests.

Solution:

i) Medicines

ii) Spices

iii) Wood

iv) Paper

v) Gum

7. Fill in the blanks:

(a) The insects, butterflies, honeybees and birds help flowering plants in .

(b) A forest is a purifier of and .

(c) Herbs form the layer in the forest.

(d) The decaying leaves and animal droppings in a forest enrich the .

Solution:

(a) The insects, butterflies, honeybees and birds help flowering plants in pollination.

(b) A forest is a purifier of air and water .

(c) Herbs form the lowest layer in the forest.

(d) The decaying leaves and animal droppings in a forest enrich the soil.

8. Why should we worry about the conditions and issues related to forests far from us?

Solution:

We should worry about the forest for the following reasons.

• A decrease in forest results in an increase in carbon dioxide content in the atmosphere. This results in global warming.
• Depletion of forests results in soil erosion
• Decrease in forest adversely affect the lives of animals living in the forest.
• Absence of forests leads to flooding more often.
• Due to the reduction of forest land will turn barren which is called desertification.

9. Explain why there is a need of variety of animals and plants in a forest.

Solution:

Variety of plants and animals in the forests helps plants to regenerate and grow. More excellent range of plants supports herbivores, which in turn serve as food for carnivores. Decomposers turn dead animals and plants into humus; thereby maintain nutrient recycling. This wide variety makes forest a dynamic living entity.

10. In Fig. 17.15, the artist has forgotten to put the labels and directions on the arrows. Mark the directions on the arrows and label the diagram using the following labels: clouds, rain, atmosphere, carbon dioxide, oxygen, plants, animals, soil, roots, water table.

Solution:

11. Which of the following is not a forest product?

(i) Gum

(ii) Plywood

(iii) Sealing wax

(iv) Kerosene

Solution:

The answer is (iv) Kerosene

12. Which of the following statements is not correct?

(i) Forests protect the soil from erosion.

(ii) Plants and animals in a forest are not dependent on one another.

(iii) Forests influence the climate and water cycle.

(iv) Soil helps forests to grow and regenerate.

Solution:

Statement (ii) Plants and animals in a forest are not dependent on one another – is incorrect

13. Micro-organisms act upon the dead plants to produce

(i) sand (ii) mushrooms (iii) humus (iv) wood

Solution:

Answer is (iii) humus

WATER : A PRECIOUS RESOURCE

 NOTES 

The upper limit of groundwater is called water table. It represents the depth of water filled area at a given place. The water table rises and falls depending upon the amount of rainwater that seeps into the groundwater and how much groundwater is drawn out for irrigation and industry. The seeping down of rainwater into the groundwater is called infiltration. The groundwater thus gets recharged by this process.

At some places, the groundwater is stored between layers of hard rock below the water table. This is aquifer which contains the groundwater usable by tubewells and handpumps. These sources however, have limited sources of water and may get exhausted if used excessively.

Exercise Questions

1. Mark ‘T’ if the statement is true and ‘F’ if it is false:

(a) The freshwater stored in the ground is much more than that present in the rivers and lakes of the world. (T/F)

(b) Water shortage is a problem faced only by people living in rural areas. (T/F)

(c) Water from rivers is the only source for irrigation in the fields. (T/F)

(d) Rain is the ultimate source of water. (T/F)

Solution:

a) True

b) False

c) False

d) False

2. Explain how groundwater is recharged.

Solution:

The rainwater and water from other sources such as rivers and ponds seep through the soil and fills the empty spaces and cracks deep below the ground. The process of seeping of water into the ground is called infiltration. The groundwater thus gets recharged by this process.

3. There are ten tubewells in a lane of fifty houses. What could be the long term impact on the water table?

Solution:

If ten tube-wells in a lane of fifty houses are situated, the groundwater will get used for domestic purposes. This results in depletion of groundwater level and water table would go down.

4. You have been asked to maintain a garden. How will you minimise the use of water?

Solution:

We can reduce the usage of water for gardening by adopting drip irrigation method. In this method, water will reach the roots of the plant drop by drop, which will reduce the wastage of water.

5. Explain the factors responsible for the depletion of water table.

Solution:

Factors responsible for the depletion of the water table are as follows:

Increase in population; Increase in population leads to increased demand for water for domestic and drinking purpose. This reduces the water table.

Industrialisation: Industries need a lot of water for manufacturing purposes. This reduces the water table.

Agriculture: Agriculture requires a lot of water for growing crops; this results in depletion of water table.

6. Fill in the blanks with the appropriate answers:

(a) People obtain groundwater through________ and ________.

(b) Three forms of water are ________, ________ and ________.

(c) The water bearing layer of the earth is ________.

(d) The process of water seepage into the ground is called ________.

Solution:

(a) People obtain groundwater through tube wells and hand pumps.

(b) Three forms of water are ice, water and vapour.

(c) The water bearing layer of the earth is Hydrosphere.

(d) The process of water seepage into the ground is called infiltration.

7. Which one of the following is not responsible for water shortage?

(i) Rapid growth of industries

(ii) Increasing population

(iii) Heavy rainfall

(iv) Mismanagement of water resources

Solution:

The answer is (iii) Heavy rainfall

8. Choose the correct option. The total water

(i) in the lakes and rivers of the world remains constant.

(ii) under the ground remains constant.

(iii) in the seas and oceans of the world remains constant.

(iv) of the world remains constant.

Solution:

The answer is (iv) of the world remains constant.

9. Make a sketch showing groundwater and water table. Label it.

Solution:

LIGHT

 NOTES

There are two types of images:
Real image: It is an image which can be obtained on a screen, e.g. the image formed on a cinema screen. When the light rays coming from an object actually meet at a point after reflection from the mirror, then it results in the formation of a real image.

Virtual image: It is an image which cannot be obtained on a screen, e.g. image formed by a plane mirror. When the light rays coming from an object appear to meet after reflection from the mirror, then it results in the formation of virtual image. It is not possible to form a virtual image on the screen because light rays actually do not pass the screen or cannot be received on a screeN

 LATERAL INVERSION- the right side of our body becomes the left side in the image while the left side of our body becomes the right side of the image. It appears as if our image has been ‘reversed side ways’ with respect to your body. The effect of reversing the sides of an object and its image is called lateral inversion.

Dispersion of Light
In the year 1665, Newton discovered by his experiments with glass prisms that white light (like sunlight) consists of a mixture of lights of seven colours. Newton found that if a beam of white light is passed through a glass prism, then the white light splits to form a band of seven colours on a white screen. The band of seven colours formed on a white screen, when a beam of white light is passed through a glass prism, is known as a spectrum of white light. The seven colours of the spectrum are Red, Orange, Yellow, Green, Blue, Indigo and Violet.

So, dispersion of light is the phenomenon of splitting up of white light into seven colours on passing through a transparent medium like a glass prism. The formation of a spectrum of seven colours indicates that white light is a mixture of seven colours. White light can be sunlight. So, now we can say that sunlight consists of seven colours.

Exercise Questions

1. Fill in the blanks:

(a) An image that cannot be obtained on a screen is called ____________.

(b) Image formed by a convex __________ is always virtual and smaller in size.

(c) An image formed by a __________ mirror is always of the same size as that of the object.

(d) An image which can be obtained on a screen is called a _________ image.

(e) An image formed by a concave ___________ cannot be obtained on a screen.

Solution:

(a) An image that cannot be obtained on a screen is called virtual image.

(b) Image formed by a convex mirror is always virtual and smaller in size.

(c) An image formed by a plane mirror is always of the same size as that of the object.

(d) An image which can be obtained on a screen is called a real image.

(e) An image formed by a concave lens cannot be obtained on a screen.

2. Mark ‘T’ if the statement is true and ‘F’ if it is false:

(a) We can obtain an enlarged and erect image by a convex mirror. (T/F)

(b) A concave lens always form a virtual image. (T/F)

(c) We can obtain a real, enlarged and inverted image by a concave mirror. (T/F)

(d) A real image cannot be obtained on a screen. (T/F)

(e) A concave mirror always form a real image. (T/F)

Solution:

a) False

b) True

c) True

d) False

e) False

3. Match the items given in Column I with one or more items of Column II.

Column-I	Column-II
(a) A plane mirror	(i) Used as a magnifying glass
(b) A convex mirror	(ii) Can form image of objects spread over a large area.
(c) A convex lens	(iii) Used by dentists to see enlarged image of teeth.
(d) A concave mirror	(iv) The image is always inverted and magnified
(e) A concave lens	(v) The image is erect and of the same size as the object.
	(vi) The image is erect and smaller in size than the object.

Solution:

Column-I	Column-II
(a) A plane mirror	(v) The image is erect and of the same size as the object.
(b) A convex mirror	(ii) Can form an image of objects spread over a large area.
(c) A convex lens	(i) Used as a magnifying glass
(d) A concave mirror	(iii) Used by dentists to see an enlarged image of teeth.
(e) A concave lens	(vi) The image is erect and smaller in size than the object.

4. State the characteristics of the image formed by a plane mirror

Solution:

Characteristics of the image formed by a plane mirror are as follows:

• Image distance and object distance are equal
• Size of object and image are equal
• The image formed is erect and virtual
• Images are laterally inverted

• 5. Find out the letters of English alphabet or any other language known to you in which the image formed in a plane mirror appears exactly like the letter itself. Discuss your findings.

  Solution:

  A, H, I, M, O, T, U, V, W, X, Y alphabets form images in a plane mirror exactly like the letter itself because these alphabets are laterally symmetric.

6. What is a virtual image? Give one situation where a virtual image is formed.

Solution:

The image that cannot be obtained on a screen is called a virtual image. The image formed by a plane mirror is virtual.

7. State two differences between a convex and a concave lens.

Solution:

Convex Lens	Concave Lens
Thick in the middle and thin at the edge	Thin in the middle and thick at the edge
Image formed is real or virtual	Image formed is virtual

8. Give one use each of a concave and a convex mirror.

Solution:

Concave mirrors are used in the headlights of cars and scooters.

Convex mirrors are used as side-view mirrors in vehicles.

. Which type of mirror can form a real image?

Solution:

The concave mirror can form a real image.

10. Which type of lens forms always a virtual image?

Solution:

Concave lens form a virtual image.

Choose the correct option in questions 11–13

11. A virtual image larger than the object can be produced by a

(i) concave lens (ii) concave mirror

(iii) convex mirror (iv) plane mirror

Solution:

The answer is (ii) concave mirror

12. David is observing his image in a plane mirror. The distance between the mirror and his image is 4 m. If he moves 1 m towards the mirror, then the distance between David and his image will be

(i) 3 m (ii) 5 m

(iii) 6 m (iv) 8 m

Solution:

The answer is (iii) 6 m

13. The rear view mirror of a car is a plane mirror. A driver is reversing his car at a speed of 2 m/s. The driver sees in his rear view mirror the image of a truck parked behind his car. The speed at which the image of the truck appears to approach the driver will be

(i) 1 m/s (ii) 2 m/s

(iii) 4 m/s (iv) 8 m/s

Solution:

The answer is (iii) 4 m/s

ELECTRIC CURRENT AND ITS EFFECT.

 NOTES

Heating Effect of Electric Current

Conductors and insulators

• Substances or materials that offer comparatively less opposition to electric current through them are called as conductors. Eg: copper, iron, water, etc.
• Substances, which offer larger opposition to electric current through them are called as insulators. Eg: rubber, wood, sand, etc.

Heating effects of electric current

• A current carrying wire gets hot whenever electric passes through it. This is the heating effect of electric current.
• The amount of heat produced in the wire depends on the material, thickness and length of the conductor.
• If a large amount of electric current passes through the wire, the wire may become so hot that it may melt and break.
• Heating effects of electricity are applied for many household appliances such as electric heaters, toasters, water heaters.
• They are also used in bulbs and used as safety devices(fuses).

• When wires are made of a material that melts on the passage of electric current are called as a fuse. Electrical fuses are used as a safety device that breaks a circuit in times of overloading. They prevent the cause of fire and damage to electrical circuits.

• An electromagnet is an artificial magnet, which produces a magnetic field around a conductor due to the passage of electric current through it.

VIDEO CLICK OPN THE ABOVE LINK TO SEE HOW ELECTRIC BELL WORKS;

WORKING OF ELECTRIC BELL

Exercise Questions

1. Draw in your notebook the symbols to represent the following components of electrical circuits: connecting wires, switch in the ‘OFF’ position, bulb, cell, switch in the ‘ON’ position, and battery

Solution:

2. Draw the circuit diagram to represent the circuit shown in Fig.14.21.

Solution:

3. Fig.14.22 shows four cells fixed on a board. Draw lines to indicate how you will connect their terminals with wires to make a battery of four cells.

Solution:

4. The bulb in the circuit shown in Fig.14.23 does not glow. Can you identify the problem? Make necessary changes in the circuit to make the bulb glow.

Solution:

In the circuit above bulb is connected on either side.

5. Name any two effects of electric current.

Solution:

i) Heating effect of electric current

ii) Magnetic effect of electric current

6. When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain.

Solution:

When the current is switched on through a wire, magnetic field is created around it hence we see deflection in the compass needle kept nearby.

7. Will the compass needle show deflection when the switch in the circuit shown by Fig.14.24 is closed?

Solution:

No , compass needle does not show deflection when the circuit is a closed, magnetic field is not created until current is flowing through the circuit.

8. Fill in the blanks:

(a) Longer line in the symbol for a cell represents its terminal.

(b) The combination of two or more cells is called a .

(c) When current is switched ‘on’ in a room heater, it .

(d) The safety device based on the heating effect of electric current is called a .

Solution:

(a) Longer line in the symbol for a cell represents its positive terminal.

(b) The combination of two or more cells is called a battery.

(c) When current is switched ‘on’ in a room heater, it produces heat .

(d) The safety device based on the heating effect of electric current is called a fuse .

9. Mark ‘T’ if the statement is true and ‘F’ if it is false:

(a) To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell. (T/F)

(b) When the electric current through the fuse exceeds a certain limit, the fuse wire melts and breaks. (T/F)

(c) An electromagnet does not attract a piece of iron. (T/F)

(d) An electric bell has an electromagnet. (T/F)

Solution:

a) False

b) True

c) False

d) True

10. Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.

Solution:

No, because plastic does not have magnetic property to get attracted to a magnet hence magnet cannot be used to separate plastic bags.

11. An electrician is carrying out some repairs in your house. He wants to replace a fuse by a piece of wire. Would you agree? Give reasons for your response.

Solution:

It is not a wise idea to replace fuse by a piece of wire, as it has very low melting point. In case of metal piece, melting point will be high and the circuit will be intact in case there is overload or overheat.

12. Zubeda made an electric circuit using a cell holder shown in Fig. 14.4, a switch and a bulb. When she put the switch in the ‘ON’ position, the bulb did not glow. Help Zubeda in identifying the possible defects in the circuit.

Solution:

Reasons maybe two

i) The connecting wire may be loose

ii) The electric cell may be used up

iii) switch may not be functioning well

iv) cell power has been exhausted

13. In the circuit shown in Fig. 14.25

(i) Would any of the bulb glow when the switch is in the ‘OFF’ position?

(ii) What will be the order in which the bulbs A, B and C will glow when the switch is moved to the ‘ON’ position?

Solution:

i) No, the bulb will not glow as the circuit is not complete when the switch is off

ii) If the switch is On, all the bulbs glow simultaneously.

MOTION AND TIME

 NOTES

SPEED-The distance travelled by an object per unit time (either in one hour, in one minute or in one second) is known as speed of the object.

SPEED =DISTANCE / TIME

NONUNIFORM AND UBIFORM MOTION-

If the speed of an object moving along a straight line beeps changing, its motion is said to be non-uniform motion.
On the other hand, an object moving along a straight line with a constant speed is said to be in uniform motion. In this case, the average speed is the same as the actual speed.

Note
(i) A sundial measures time by the position of the shadow cast by the sun.
(ii) The device which uses the flow of sand from one glass bulb to another in order to measure time is known as a sand clock
(iii) A device which uses the rate at which water drip from one vessel to another measure time interval is known as a water clock

imple Pendulum
A simple pendulum consists of a small metal ball called bob which is suspended by a long thread from rigid support such that bob is free to swing back and forth. The to and fro motion of a simple pendulum is an example of periodic or oscillatory motion. Galileo was the first person to study the motion of a pendulum.

Speedometer and Odometer
The speedometer is an instrument on a vehicle’s dashboard which indicates the speed of the vehicle when it is moving. This instrument tells us the speed of a running vehicle at that instant of time in kilometre per hour.

QUESTION ANSWERS AND EXCRCISE

Q.1.Classify the following as motion along a straight line, circular or oscillatory motion :
(i) Motion of your hands while running.
(ii) Motion of a horse pulling a cart on a straight road.
(iii) Motion of a child in a merry-go-round. •
(iv) Motion of a child on a see-saw.
(v) Motion of the hammer of an electric bell.
(vi) Motion of a train on a straight bridge.
Ans.(i) Oscillatory motion
(ii) Linear motion
(iii) Circular motion
(iv) Oscillatory motion
(v) Oscillatory motion
(vi) Linear motion

.2.Which of the following are not correct?
(i) The basic unit of time is second.
(ii) Every object moves with a constant speed.
(iii) Distances between two cities are measured in kilometers.
(iv) The time period of a given pendulum is not constant.
(v) The speed of a train is expressed in m/h
Ans. (ii), (iv), (v)

Q.3.A simple pendulum takes 32s to complete 20 oscillations, what is the time period of the pendulum?
Ans. Time taken to complete 20 oscillations = 32 s
Time taken to complete 1 oscillation = 32/20 s = 1.6 s
Time period of a pendulum is time taken by it to complete 1 oscillation.
Time period of pendulum is 1.6 seconds.

Q.4.The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.
Ans.Distance = 240 km
Time taken = 4 hours
Speed =Distance covered/time taken = 240km/4 hammer
=60 km/h
Speed of train =60 km/h

Q.5.The odometer of a car reads 57321.0 km when the clock shows the time 08:30 AM. What is the distance moved by the car, if at 08:50 AM, the odometer reading has changed to 57336.0 km? Calculate the speed of the car in km/min during this time. Express the speed in km/h also.
Ans.Distance = 57336.0 km – 57321 km =15 km
Speed in km/min =15km/20 min = 3/4 km/min

Speed in km/hr =15 km/1/3 hr
=(15 x 3) km/hr
=45 km/hr.

Q.6.Salma takes 15 minutes from her house to reach her school on a bicycle. If the bicycle has a speed of 2 m/min, calculate the distance between her house and the school.
Ans.Time taken =15 min
Speed = 2 m/min .
Distance = speed x time = 2 x 15 = 30 m
Distance between Salma’s school and her house is 30 m.

Q.7.Show the shape of the distance-time graph for the motion in the following cases :
(i) A car moving with a constant speed.
(ii) A car parked on a side road
Ans.

Q.8. Which of the following relations is correct?
(i) Speed = Distance Time
(ii) Speed = Distance/Time
(iii)Speed – Time/Distance
(iv)Speed = 1/Distance Time
Ans. (ii) Speed = Distance/Time is correct

Q.9.The basic unit of speed is:
(i) km/min (ii) m/min (iii) km/h (iv) m/s
Ans. (iv) m/s

Q.10.A car moves with a speed of 40 km/h for 15 minutes and then with a speed of 60 km/h for the next 15 minutes. The total distance covered by the car is:
(i) 100 km (ii) 25 km (iii) 15 km (iv) 10 km
Ans.(ii) 25 km

Q.11.Suppose the two photographs, shown in fig. 13.1 and fig. 13.2 of NCERT had been taken at an interval of 10 seconds. If a distance of 100 metres is shown by 1 cm in these photographs, calculate the speed of the blue car.
Ans.0.1 cm/s or 10 m/s

Q.12.Fig 13.10 shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?

Ans. ‘A’ is moving faster.

Q.13.Which of the following distance-time graphs shows a truck moving with speed which is not constant?

Ans. (iii)