Class 7 Science Chapter-14 Solutions

      CLASS-7 SCIENCE SOLUTION

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                  CHAPTER-14

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      ELECTRIC CURRENT AND ITS                              EFFECTS

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.

Class 7 Science Chapter-13 Solutions

      CLASS-7 SCIENCE SOLUTION

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                  CHAPTER-13

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                 MOTION AND TIME

Exercise Questions

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.

Solution:

i) oscillatory

ii) Motion along a straight line

iii) Circular motion

iv) Oscillatory motion

v) Oscillatory motion

vi) Motion along a straight line.

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 constant.

(v) The speed of a train is expressed in m/h.

Solution:

Incorrect statements are:

(ii) Every object moves with a constant speed.

(iv) The time period of a given pendulum is constant.

(v) The speed of a train is expressed in m/h.

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

Solution:

Number of oscillations = 20

Total time taken to complete 20 oscillations = 32 s



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

Solution:

Distance between two stations = 240 kms

Total time take = 4 hrs/240 minutes



= 60 km/h

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.

Solution:

Initial reading of the odometer = 57321.0

Final reading of the odometer = 57336.0

Distance covered by the car = Final reading of the odometer – Initial reading of the odometer

= 57336.0 – 57321.0 = 15 kms

Starting time of car is 8:30 and it stops at 8: 50

Hence, time taken by car = 20 mins



= 45 km/h

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.

Solution:

Time taken by Salma to reach her school by bicycle = 15 mins= 15 x 60 = 90 s

Speed of Salma’s bicycle= 2m/s



Distance covered = speed x time taken

= 2 x 900 = 1800 m

1000m = 1 km



= 1.8 kms

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.

Solution:




8. Which of the following relations is correct?

(i) Speed = Distance × Time

(ii) Speed = Distance/Time

(iii) Speed = Time/Distance

(iv) Speed = 1/Distance x Time

Solution:

Answer is (ii) Speed = Distance/Time

9. The basic unit of speed is:

(i) km/min

(ii) m/min

(iii) km/h

(iv) m/s

Solution:

Answer is (iv) m/s

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

Solution:

The answer is (ii) 25 km

Calculation:

When the speed of the car is 40 km/h

Time taken = 15 min = 15/60 = 0.25 h



Distance covered d1 = speed x time taken

= 40 x 0.25 = 10 kms

When the speed of the Car is 60 km/ h



Distance covered d2 = speed x time taken

= 60 x 0.25= 15 kms

Total distance covered by the car = d1 + d2

= 10 + 15

= 25 kms

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 fastest car.



Solution:

The distance covered by the blue car (as evident from the photograph) from one horizontal white strip to another, which is measured by scale is 1.2 cm.

It is given that 1 cm is equivalent to 100 m.

Therefore, 1.2 cm is equivalent to 120 m.

Distance travelled by the car = 120 m

Time taken to cover this distance = Time interval between the two photographs = 10 s



= 120/10

= 12 m/s

12. Fig. 13.15 shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?



Solution:

Vehicle A is moving faster than vehicle B.

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




Solution:

Answer is iii)

Class 7 Science Chapter-12 Solutions

      CLASS-7 SCIENCE SOLUTION

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                  CHAPTER-12

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       REPRODUCTION IN PLANTS

Exercise Questions

1. Fill in the blanks:
(a) Production of new individuals from the vegetative part of parent is called_____________.
(b) A flower may have either male or female reproductive parts. Such a flower is called_____________.
(c) The transfer of pollen grains from the anther to the stigma of the same or of another flower of the same kind is known as _____________.
(d) The fusion of male and female gametes is termed as _____________.
(e) Seed dispersal takes place by means of _____________, _____________ and _____________.

Solution:
(a) Production of new individuals from the vegetative part of parent is called vegetative propogation.
(b) A flower may have either male or female reproductive parts. Such a flower is called unisexual.
(c) The transfer of pollen grains from the anther to the stigma of the same or of another flower of the same kind is known as Pollination.
(d) The fusion of male and female gametes is termed as fertilisation.
(e) Seed dispersal takes place by means of wind, water and animals.

2. Describe the different methods of asexual reproduction. Give examples.

Solution:
Asexual modes of reproduction are as follows
Vegetative propagation:
A plant can produce new plants from vegetative parts of the plant like roots, stems.
Budding:
It involves the formation of a new individual from a bulb-like projection called a bud.
Fragmentation:
New organisms are formed from the fragments of the parent body.
Spore formation:
Plants reproduce by the formation of spores.

3. Explain what you understand by sexual reproduction.

Solution:
Sexual reproduction is a method where male and female gametes fuse to form a new individual. In plants, stamens and pistils are male and female reproductive organs which bear the anthers and ovary respectively.

4. State the main difference between asexual and sexual reproduction.
Solution:

Asexual reproduction Sexual reproduction
It requires only one parents Requires a male and female parent
Daughter cells formed are identical to parents and to each other. Newly formed offsprings show variations in comparision to the parents.
Special reproductive organs are not required Special reproductive organs are required
Ex: Yeast, rose, jasmine Ex: Insects, animals


5. Sketch the reproductive parts of a flower.

Solution:

6. Explain the difference between self-pollination and cross-pollination.

Solution:

Self-pollination Cross-pollination
It involves the transfer of pollen from the stamen to the pistil of the same flower. It involves the transfer of pollen from the stamen of one flower to the pistil of another flower.
Self-pollination occurs only in bi-sexual flowers It occurs in both unisexual and bisexual flowers


7. How does the process of fertilisation take place in flowers?

Solution:
The process of fusion of male and female gametes (to form a zygote) is called fertilisation. The zygote develops into an embryo and embryo undergoes mitotic cell division to form seeds.

8. Describe the various ways by which seeds are dispersed.

Solution:
Seeds and fruits of plants are carried away by wind, water and animals. Winged seeds such as those of drumstick and maple, light seeds of grasses or hairy seeds of aak (Madar) and hairy fruit of sunflower, get blown off with the wind to faraway places. Some seeds are dispersed by water. These fruits or seeds usually develop floating ability in the form of spongy or fibrous outer coat as in coconut. Some seeds are dispersed by animals, especially spiny seeds with hooks which get attached to the bodies of animals and are carried to distant places. Examples are Xanthium and Urena. Some seeds are dispersed when the fruits burst with sudden jerks. The seeds are scattered far from the parent plant. This happens in the case of castor and balsam.

9. Match items in Column I with those in Column II: Column I Column II

Column-I Column-II
(a) Bud (i) Maple
(b) Eyes (ii) Spirogyra
(c) Fragmentation (iii) Yeast
(d) Wings (iv) Bread mould
(e) Spores (v) Potato
(vi) Rose


Solution:

Column-I Column-II
(a) Bud (iii) Yeast
(b) Eyes (v) Potato
(c) Fragmentation (ii) Spirogyra
(d) Wings (i) Maple
(e) Spores (iv) Bread mould


10. Tick the correct answer:

(a) The reproductive part of a plant is the
(i) leaf (ii) stem (iii) root (iv) flower

(b) The process of fusion of the male and the female gametes is called
(i) fertilisation (ii) pollination (iii) reproduction (iv) seed formation

(c) Mature ovary forms the

(i) seed (ii) stamen (iii) pistil (iv) fruit

(d) A spore-producing organism is
(i) rose (ii) bread mould (iii) potato (iv) ginger

(e) Bryophyllum can reproduce by its

(i) stem (ii) leaves (iii) roots (iv) flower

Solution:
a) (iv) flower
b) (i) fertilization
c) (iv) fruit
d) (ii) bread mould
e) (ii) leaves

Class 7 Science Chapter-11 Solutions

      CLASS-7 SCIENCE SOLUTION

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                  CHAPTER-11

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      TRANSPORTATION IN ANIMALS                      AND PLANTS

Exercise Questions

1. Match structures given in Column I with functions given in Column II.

Column- I	Column-II
(i) Stomata	(a) Absorption of water
(ii) Xylem	(b) Transpiration
(iii) Root hairs	(c) Transport of food
(iv) Phloem	(d) Transport of water
	(e) Synthesis of carbohydrates

Solution:

Column- I	Column-II
(i) Stomata	(b) Transpiration
(ii) Xylem	(d) Transport of water
(iii) Root hairs	(a) Absorption of water
(iv) Phloem	(c) Transport of food

2. Fill in the blanks.

(i) The blood from the heart is transported to all parts of the body by the .

(ii) Haemoglobin is present in cells.

(iii) Arteries and veins are joined by a network of .

(iv) The rhythmic expansion and contraction of the heart is called .

(v) The main excretory product in human beings is .

(vi) Sweat contains water and .

(vii) Kidneys eliminate the waste materials in the liquid form called .

(viii) Water reaches great heights in the trees because of suction pull caused by .

Solution:

(i) The blood from the heart is transported to all parts of the body by the arteries .

(ii) Haemoglobin is present in red blood cells.

(iii) Arteries and veins are joined by a network of capillaries.

(iv) The rhythmic expansion and contraction of the heart is called heartbeat.

(v) The main excretory product in human beings is urea .

(vi) Sweat contains water and salts .

(vii) Kidneys eliminate the waste materials in the liquid form called urine .

(viii) Water reaches great heights in the trees because of suction pull caused by transpiration .

3. Choose the correct option:

(a) In plants, water is transported through

(i) xylem

(ii) phloem

(iii) stomata

(iv) root hair

(b) Water absorption through roots can be increased by keeping the plants

(i) in the shade

(ii) in dim light

(iii) under the fan

(iv) covered with a polythene bag

Solution:

a) i) Xylem

b) iii) under the fan

4. Why is transport of materials necessary in a plant or in an animal? Explain.

Solution:

Transport of materials is necessary in a plant or an animal for the following reasons:
To transport food to various parts of the plant
Animals need to transport wastes to parts from where they can be removed.

5. What will happen if there are no platelets in the blood?

Solution:

If there are no platelets, then blood will not clot as platelets release blood clotting factor at the site of injury and stops further bleeding.

6. What are stomata? Give two functions of stomata.

Solution:

Tiny pores present on the leaf surface are known as stomata.

Functions of stomata
Helps in exchange of gases
Evaporation of water through leaves occurs due to stomata.

7. Does transpiration serve any useful function in the plants? Explain.

Solution:

Transpiration serves the following functions in plants
It helps in lowering temperature of plants, thus preventing heat injury of plants.
Helps in transpiration pull, which helps in raining water in higher plants.
It also causes loss of water absorbed by plants.

8. What are the components of blood?

Solution:

Red blood cells, white blood cells, platelets and plasma.

9. Why is blood needed by all the parts of a body?

Solution:

Blood is a significant part of transport system in our body, and we need blood for the following reasons:
For the transport of oxygen to all parts of our body
To expel out carbon dioxide from our body
To transmit heat thus helping in the regulation of body temperature.
It is required to fight out infections and diseases.

10. What makes the blood look red?

Solution:

Haemoglobin, a red pigment present in the blood makes it look red.

11. Describe the function of the heart.

Solution:

The heart is an organ which beats continuously to act as a pump for the transport of blood, which carries other substances with it. The heart has four chambers. The two upper chambers are called the atria (singular: atrium), and the two lower chambers are called the ventricles. The partition between the chambers helps to avoid mixing up of blood-rich in oxygen with the blood-rich in carbon dioxide. Blood flows from the heart to the lungs and back to the heart from where it is pumped to the rest of the body.


12. Why is it necessary to excrete waste products?

Solution:

When our cells perform their functions, certain waste products are released. These are toxic and hence need to be removed from the body.

13. Draw a diagram of the human excretory system and label the various parts.

Solution: