Ch 18 : Wastewater Story

                                                                              Waste water  Story

1. Fill in the blanks:
(a) Cleaning of water is a process of removing ……………….

Answer: Contaminants

(b) Wastewater released by houses is called ……………

Answer: Sewage

(c) Dried ……………. is used as manure.

Answer: Sludge

(d) Drains get blocked by …………….. and …………………

Answer: Oil and fat

2. What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.

Answer: The liquid waste which has water as its largest component; along with various types of impurities; is called sewage. Discharging untreated sewage into rivers or seas contaminates the water of these water bodies. Contaminated water is dangerous for aquatic plants and animals. So, it is harmful to discharge untreated sewage into rivers or seas.

3. Why should oils and fats be not released in the drain? Explain.

Answer: Oil and fats can clog the drains. In open drains, they block the pores in the soil and thus hamper the filtration by soil. Hence, oil and fats should not be released in the drain.

4. Describe the steps involved in getting clarified water from wastewater.

Answer: The following steps are involved in clarifying wastewater:

• Insoluble waste is removed by filtration and sedimentation processes.

• Bacteria are allowed to grow through the process of aeration. Bacteria eat away human waste from the wastewater.

• Chlorination is used to kill the germs in clarified water. After this step, the water becomes fit even for human consumption.

5. What is sludge? Explain how it is treated.

Answer: The solid waste which settles at the bottom of the sedimentation tank is called sludge. The sludge is further treated by the process of aeration. This helps in growth of bacteria which eat away the human waste.

6. Untreated human excreta is a health hazard. Explain.

Answer: Untreated human excreta contains many microbes which can cause deadly diseases; like cholera, diarrhea, jaundice and typhoid. The germs of these diseases can easily reach human population through insects and through contaminated food and water. Thus, untreated human excreta are a health hazard.

7. Name two chemicals used to disinfect water.

Answer: Bleaching Powder and Chlorine Tablets

8. Explain the function of bar screens in a wastewater treatment plant.

Answer: Bar screens are large filters which are placed in the form of vertical screens. Large solid wastes; like sticks, pebbles, sand, cans, plastic bottles, plastic bags, etc. are filtered out when the wastewater moves through the bar screen.

9. Explain the relationship between sanitation and disease.

Answer: Sanitation and disease are closely related. Lack of sanitation leads to unhygienic conditions; which creates many communicable diseases. Maintenance of sanitation removes the chances of such diseases.

10. Outline your role as an active citizen in relation to sanitation.

Answer: My role as an active citizen can be in maintaining sanitation in the neighbourhood and at public places. For this, I shall follow these steps:

• Throwing garbage at designated places and in garbage bins.

• Preventing clogging of drains by not releasing oil and fat and solid waste into the drain.

• Using a dustbin to throw trash at public places.

• By not spitting at public places.

Ch 17 : Forest: Our Lifeline

                                    Forest: Our Lifeline

 

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

Answer: Animals which live in the forest help it grow and regenerate in following ways:

(a) By eating vegetation they clear land for fresh growth

(b) Animals help flowering plants in pollination and seed dispersal

(c) Dead remains of animals make humus after decomposition. This increases soil fertility

Question: 2 - Explain how forests prevent floods.

Answer: Trees slow down the movement of running water and thus help in preventing floods.

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

Answer: The organisms which decompose the dead remains of plants and animals are called decomposers. Fungi and bacteria are examples of decomposers. They clear the debris of dead remains and convert them into humus which enriches the topsoil.

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

Answer: Green plants utilize carbon dioxide during photosynthesis and release oxygen in the process. Thus, the green plants maintain the balance of carbon dioxide and oxygen in the atmosphere.

Question: 4 - Explain why there is no waste in a forest.

Answer: Forest works like a self sustaining system. Whatever is produced in the forest is utilized by different components of the forest. Even the waste is converted into beneficial substances in a forest. Due to this, there is no waste in a forest.

Question: 5 - List five products we get from forests?

Answer: Following are the five products we get from forests:

Timber for furniture, firewood, lac, resin, honey

Question: 6 - Fill in the blank:
(a) The insects, butterflies, honeybees and birds help flowering plants in ………….

Answer: Pollination

(b) A forest is a purifier of ……………and ………………

Answer: Water and air

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

Answer: Understory

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

Answer: Topsoil

Question: 7 - Why should we worry about the conditions and issues related to forests far from us?

Answer: Forests affect the global environment in a great way. For example; reduced forest cover in a particular area leads to global warming which affects the whole earth. This is the reason we should worry about the conditions and issues related to forests which are even far from us.

Question: 8 - Explain why there is a need of variety of animals and plants in a forest.

Answer: Different animals and plants play different role in the system of a forest. For example; herbivores are needed to eat green plants and to provide food for the carnivores. Similarly, carnivores are needed to eat the herbivores and check their population. That is why there is a need of variety of animals and plants in a forest.

Question: 9 - Which of the following is not a forest product?
(i) Gum
(ii) Plywood
(iii) Sealing wax
(iv) Kerosene

Answer: (iv) Kerosene

Question: 10 - 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.

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

 

Ch 16 : Water: A Precious Resource

                              Water: A Precious Resource

 

Question: 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)
(b) Water shortage is a problem faced only by people living in rural areas. (F)
(c) Water from rivers is the only source for irrigation in the fields. (F)
(d) Rain is the ultimate source of water. (T)
Question: 2 - Explain how groundwater is recharged?

Answer: The surface water seeps down the ground through the porous layers of the soil. This process is called infiltration and is responsible for recharging the groundwater.

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

Answer: Ten tube-wells in a lane of fifty houses can lead people to mindlessly exploit the groundwater. This can lead to depletion of the water table in the long run.

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

Answer: Drip irrigation can be used in the garden to minimize the use of water.

Question: 5 - Explain the factors responsible for the depletion of water table.

Answer: Following factors are responsible for depletion of water table:

There is more demand of water due to increasing population. Increasing population means there is ever increasing demand of water for various human activities.

Deforestation has removed a large portion of forest cover. This has disturbed the natural process of recharging the groundwater.

While demand for water has increased, the supply has reduced. The mismatch between demand and supply is mainly responsible for depletion of water table.

Question: 6 - Fill in the blanks with the appropriate answers:
(a) People obtain groundwater through________ and ________.

Answer: Wells and tube-wells

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

Answer: Ice, water and vapour

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

Answer: Aquifer

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

Answer: Infiltration

Question: 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

Answer: (iii) Heavy rainfall

Question: 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.

Answer: (iv) Of the world remains constant

 

Ch 15 : Light

                                                                                      Light

Question: 1 - Fill in the blanks:

1. An image that cannot be obtained on a screen is called ____________.
   
   Answer: Virtual
   
2. Image formed by a convex __________ is always virtual and smaller in size.
   
   Answer: Mirror
   
3. An image formed by a __________ mirror is always of the same size as that of the object.
   
   Answer: Plane
   
   
4. An image which can be obtained on a screen is called a _________ image.
   
   Answer: Real
   
   
5. An image formed by a concave ___________ cannot be obtained on a screen.
   
   Answer: Lens
   

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

1. We can obtain an enlarged and erect image by a convex mirror.
   (F)
2. A concave lens always form a virtual image.
   (T)
3. We can obtain a real, enlarged and inverted image by a concave mirror.
   (F)
4. A real image cannot be obtained on a screen.
   (F)
5. A concave mirror always form a real image.
   (F)

Question: 3 -Match the items given in Column I with one or more items of Column II.
Question: 4 -State the characteristics of the image formed by a plane mirror.

Answer: In case of plane mirror, the image is erect, virtual and of same size as the object.

Question: 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.

Answer: Some examples: A, H, I, M, O, T, U, V, W and X

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

Answer: The image which cannot be obtained on a screen is called virtual image. For example, virtual image is always formed in case of plane mirror and convex mirror.

Question: 7 -State two differences between a convex and a concave lens.

Answer: A convex lens can make enlarged image, while a concave lens would always make smaller image. A convex lens usually makes real image, while a concave lens always makes a virtual image.

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

Answer: (a) Concave mirror is used in solar furnace. (b) Convex mirror is used in rear view mirrors.

Question: 9 -Which type of mirror can form a real image?

Answer: Concave mirror

Question: 10 - Which type of lens forms always a virtual image?

Answer: Concave lens

Choose the correct option in questions 11–13
Question: 11 - A virtual image larger than the object can be produced by a

1. Concave lens
2. Concave mirror
3. Convex mirror
4. Plane mirror

Answer: (c) Concave mirror

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

1. 3 m
2. 5 m
3. 6 m
4. 8 m

Answer: (a) 3 m

Question: 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

1. 1 m/s
2. 2 m/s
3. 4 m/s
4. 8 m/s

Answer: (b) 2 m/s

Ch 14 : Electric Current and Its Effects

               Electric Current and Its Effects

 

Question: 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.

Answer:

Question: 2 - Draw the circuit diagram to represent the circuit shown in the following figure.

Answer:

Question: 3 - The following figure 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.

Answer:

Question: 4 - The bulb in the circuit shown in the following figure does not glow. Can you identify the problem? Make necessary changes in the circuit to make the bulb glow.

Answer: The positive terminals of both the cells are together and that is why the bulb is not glowing. The cells should be kept in a way that the positive terminal of one cell is near the negative terminal of another cell; to make the bulb glow.

Question: 5 - Name any two effects of electric current.

Answer: The two effects of electric current are; heating effect and magnetic effect.

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

Answer: This happens because when electric current passes through a conducting wire, a magnetic field is created around the wire. The magnetic field causes deflection in the magnetic compass.

Question: 7 - Will the compass needle show deflection when the switch in the circuit shown by following figure is closed?

Answer: Yes

Question: 8 - Fill in the blanks:

1. Longer line in the symbol for a cell represents its …………..terminal.
   
   Answer: Positive
   
2. The combination of two or more cells is called a ……………
   
   Answer: Battery
   
3. When current is switched ‘on’ in a room heater, it ……………….
   
   Answer: heats up
   
4. The safety device based on the heating effect of electric current is called a ……………
   
   Answer: Electric fuse

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

1. To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell. (F)
2. When the electric current through the fuse exceeds a certain limit, the fuse wire melts and breaks. (T)
3. An electromagnet does not attract a piece of iron. (F)
4. An electric bell has an electromagnet. (T)

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

Answer: Since plastic is a non-magnetic material, so electromagnet cannot be used to separate plastic bags from a garbage heap.

Question: 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.

Answer: A special wire with low melting point should be used for the fuse wire and any other wire would not serve the purpose. Hence, I would not agree with the electrician.

Question: 12 - Zubeda made an electric circuit using a cell holder shown in Fig. 14.4 (in the chapter), 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.

Answer: There can following possibilities:

• The terminals of cells are not in correct position.
• The connections are loose.
• The bulb may have fused.

Question: 13 -In the circuit shown in the following figure:

1. Would any of the bulb glow when the switch is in the ‘OFF’ position?
   
   Answer: None of the bulbs would glow.
   
2. What will be the order in which the bulbs A, B and C will glow when the switch is moved to the ‘ON’ position?
   
   Answer: All the bulbs would glow at once.

 

Ch 13 : Motion and Time

                                           Motion and Time

 

Question: 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.

Answer: (i) Periodic motion or Oscillatory motion

(ii) Along a straight line (Linear motion)

(iii) Circular motion

(iv) Periodic motion or oscillatory motion

(v) Periodic motion or oscillatory motion

(vi) Linear motion

Question: 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 kilometres.
(iv) The time period of a given pendulum is not constant.
(v) The speed of a train is expressed in m/h.

Answer: (ii), (iv) and (v)

Question: 3. A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?

Answer:

Given, Number of oscillation = 20

Time taken = 32 second

We know that,

Question: 4. The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.

Answer: Given, distance = 240 km

Time taken = 4 hour

We know that,

Question: 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.

Answer:

Given,

Initial reading of odometer = 57321.0 km

Final reading of odometer = 57336.0 km

Initial time = 08:30 AM

Final time = 08:50 AM

Thus,

Distance covered = Final reading of odometer – Initial reading of odometer

  = 57336.0 km – 57321.0 km = 15 km

Total time taken = Final time – Initial time = 08:50 AM – 08:30 AM = 20 minute

So, speed = 0.75 km/minute or 45km/hour

Question: 6. Salma takes 15 minutes from her house to reach her school on a bicycle. If the bicycle has a speed of 2 m/s, calculate the distance between her house and the school.

Answer:

Given, Speed = 5 m/s

Time taken = 15 minute

Distance =?

We know that,

Question: 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.

Answer:

Question: 8. Which of the following relations is correct?
Question: 9. The basic unit of speed is:
(i) km/min (ii) m/min (iii) km/h (iv) m/s

Answer: (iv) m/s

Question: 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

Answer:

Given,

Speed for first 15 minute = 40km/h

Speed for next 15 minute = 60 km/h

We know that,

Distance = Speed X Time

Therefore, Distance covered in first 15 minute i.e. 0.25 hour = 40 km/h X 0.24 hour = 10 km

Distance covered in next 15 minute = 60 km/h X 0.25 hour = 15 km

Thus, total distance covered = 10 km + 15 km = 25 km

Hence, Answer (ii) is correct

Question: 11. Suppose the two photographs, shown in Fig. 13.1 and Fig. 13.2 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.

Answer:

Figure in question is given from text book.

Do the following steps to calculate the speed:

Measure the distance cover by blue car.

Multiply the distance measured in cm by 100 to get the distance covered by car in meter.

Divide th distance in meter by 10 second (time given in question).

Result will be the speed of car in meter/second.

Suppose the distance of car is 3.5 cm.

Thus, Distance covered by car = 3.5 x 100 = 350 meter.

Time (given in question) = 10 second

Question: 12. Figure given here shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?

Answer: Vehicle A is moving faster which is evident from higher slope for distance time graph of this vehicle; compared to that of the other vehicle.

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

Answer: (iii) The slope of the graph in this option is not a straight line and hence it does not show a uniform motion.