Std.7 Math (PRACTICE PAPER)

                                                             PRACTICE PAPER

Q.I) Choose the correct alternative with the alphabet against the sub-question number:     04 marks

1.The LCM of 4 and 5 is ________

A) 20     B) 15      C) 5

2.If the sum of the measures of two angles is 90° then they are known as ........... angles.

     A)  supplementary    B)  complementary     C)  zero

3) The quotient of two negative integers is a ........... integer.

A) positive  B) negative  C)  infinite 

4. Two numbers which have only 1 as a common factor are said to be ______ number.

A) composite number  B) co-prime number  C)  small number

Q) II Attempt the following  (Any 3)                                                                                 06 marks

1. Divide:  A)  (- 98) ÷ (- 14)      B)  (-10) ÷  (-10)

2.Find the LCM of 15 and 30

3.The product of two digit numbers is 765 and the GCD = 3. What is their LCM ?

4. Name the pairs of opposite rays in the figure alongside.

Q.III)   Solve (Any 2)                                                                                                      06 marks

1.Write the measures of the supplements of the angles given below

    a) 30° b) 60°  c) 40°

2.a) Which number is neither a prime nor a composite number.?

   b) Which are the even prime numbers?

   c) Say true or false.

      2 is the HCF of any two consecutive even numbers. 

         

3.Observe the figure and complete table.

Q.IV) Solve (Any 1)                                                                                                           04 marks

1.Write four divisions of integers such that the fractional form of each will be 24/5.

2. A)Draw a number line and show the following numbers on number line

           -3 , 2 

    B) Find HCF by the division method and reduce to the simplest form.

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Std.7 Practice Paper (Science)

                                                           PRACTICE PAPER 

_________________________________________________________________________________________

Q.1 A Choose the correct alternative and write it along with its allotted alphabet. [2 marks]

        1) Plant food is produced by a special process known as  __________  

            (a) photosynthesis   (b) evaporation  (c) condensation 

        2) The part that grows from inside the seed towards the soil is called the __________

            (a) radical (b) herbs (c) plumule

B] Answer the following:                                             [2 marks]

        1) True or False:

             Androecium is a male reproductive organ.

        2)  Match the following:

Q.2 A. Give scientific reasons (Any 1)     [2marks]

       1) Why do living organisms need nutrition ?

       2) Corn is an example of monocot seed.

       3) Nowadays, food is served buffet style during large gatherings.

Q.2 B] Answer the following (Any 2)        [4 marks]

      1) Draw a neat and labelled diagram of parts of leaf.

      2) Name the following:(Who am I ?)

       i) I transport minerals and water from the root to all aerial parts of the plant. 

       ii) I transport the food (glucose, etc.) from the leaves to other parts of the  plant where it is either consumed or stored..

 3) Complete the table:

Q.3) Answer the following (Any 2) [6 marks]

     1) Choose the appropriate word from the bracket and rewrite the paragraph.

(host ,chlorophyll ,Scavengers, photosynthesis, parasitic, decomposers, saprophytic, insects.)

Due to the absence of ........., the cuscuta is completely dependent on the ........ plant. Hence, it is said to be a completely ........ plant.

Plants which obtain the food from dead and decaying bodies of other organisms are called ...... plants.

........ obtain their food from dead bodies of animals, for example, vulture, 

crow, hyena, etc.  and. ....... are some microbes which obtain their food by decomposing the dead bodies of organisms or other materials. 

  2) Write a note on Pasteurisation.

  3) Describe any three parts of flower.

4. Classify according to food-type.

cow, lion, sparrow, frog, cockroach, tick.

Q.4) Answer the following (Any 1)          [4 marks]

1.Write the practical tests to find out if food has been adulterated or not.

For Milk,Rava,Turmeric powder and Red chilly powder.

2. Identify the parts of stem and write any two functions of stem.

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Poster making competition

Dear Students,

SAGH is glad to announce Poster making and slogan writing competition on the occasion of swastha bharat abhiyan.

As you are aware about harmful effects of intoxicant material, highlighting the health and other risks associated with tobacco use.

On this occasion of great significance, we are glad to announce this competition to explore the creative instinct of students from class7th to 8th and encourage them to portray their ideas on “health and other risks associated with tobacco use”.

PARTICIPATION GUIDELINES

The creative participation is open for students of classes as per following two categories;(Only SAGH, Chembur)

1. 7th

2. 8th

LANGUAGE

Creative entries must be written in English,Marathi or Hindi only.

IMPORTANT DATES

• Start Date: 12th July 2023

• Last Date: 14th July, 2023

MODE OF SUBMISSION:

• A3 or A4 sheet may be used for Poster.

• Write-up text (slogan) of the Poster should be submitted in readable font of English/Hindi/Marathi and it should be written on the poster itself.

Thank you

Image credit:Internet 

Std. 8. Force and Pressure

Question 1:

Write the word in the blank space.
A. The SI unit of force is_________ (Dyne, Newton, Joule)
B. The air pressure on our body is equal to __________ pressure (Atmospheric, sea bottom, space)
C. For a given object, the buoyant force in liquids of different ________ is__________ (the same, density, different, area)
D. The SI unit of pressure is_______ (N/m³ , N/m², kg/m², pa/m²) 

ANSWER:

A. The SI unit of force is Newton.
B. The air pressure on our body is equal to atmospheric pressure.
C. For a given object, the buoyant force in liquids of different density is different.
D. The SI unit of pressure is N/m².

Page No 22:

Question 2:

Make a match 

A group	B group
1. Fluid	a. Higher pressure
2. Blunt knife	b. Atmospheric pressure
3. sharp needle	c. Specific gravity
4.Relative density	d. Lower pressure
5. Hecto pascal	e. Same pressure in all directions

ANSWER:

A group	B group
1. Fluid	e. Same pressure in all directions
2. Blunt knife	d. Lower pressure
3. sharp needle	a. Higher pressure
4. Relative density	c. Specific gravity
5. Hecto pascal	b. Atmospheric pressure

Page No 22:

Question 3:

Answer the following questions in brief.
A. A plastic cube is released in water.  Will it sink of come to the surface of watet?
B. Why do the load carrying heavy vehicles have large number of wheels?
C. How much pressure do we carry on our heads? why don't we feel it?

ANSWER:

(a) The plastic cube is going to float on the surface of water as its density is less than that of water.

(b) We know, $\mathrm{Pressure}=\frac{\mathrm{Force}}{\mathrm{Area}}$
So, greater the area of contact between two surfaces, lesser will be the pressure. So, the load carrying heavy vehicles have large number of wheels so that the pressure on the road is reduced due to larger contact area. Also, using large number of wheels ensures that the force due to the load is shared among the tyres and no single tyre is under stress.

(c) We carry atmospheric pressure of about 10⁵ Pa on our heads. We don't feel it because this atmospheric pressure is balanced by the pressure created by the air and blood inside our body. 

Page No 22:

Question 4:

Why does it happen?
A. A ship dips to a larger depth in fresh water as compared to marine water.
B. Fruits can easily be cut with a sharp knife.
C. The wall of a dam is broad at its base.
D. If a stationary bus suddenly speeds up, passengers are thrown in the backward direction.

ANSWER:

A. The density of marine water is more than the fresh water due to which the buoyant force on the ship in marine water is more than the fresh water. Hence, the ship dips to a larger depth in fresh water as compared to marine water.

B. Since the sharp edged knife makes lesser contact with the fruits to be cut, thus the pressure exerted by it on the fruit is very large. Because of this large pressure, fruits are easily cut with a sharp knife.

C. We know pressure of liquid increases with depth. So, the wall of a dam is made broader at its base so that it is able to withstand the heavy pressure exerted by the river water.

D. If a stationary bus suddenly speeds up, passengers are thrown in the backward direction. This is because initially the whole body of a passenger inside the bus was in the state of rest. But, when the bus suddenly starts or speeds up, the lower half of the passenger's body comes in motion in the forward direction but the upper half still remains at rest due to inertia of rest. Hence, the passengers are thrown backward when a stationary bus suddenly speeds up.

Page No 22:

Question 5:

Complete the following tables.

Mass(Kg)	Volume (m3)	Density(kg/m3)
350	175	-
-	190	4

 

Density of Metal (kg/m3)	Density of water (kg/m3)	Relative Density
	103	5
8.5$\times$103	103	-

 

weight(N)	Area (m2)	Pressure(Nm−2)
-	0.04	20,000
1500	500	-

ANSWER:

We know, $\mathrm{Density}=\frac{\mathrm{Mass}}{\mathrm{Volume}}$
So, using above formula, we can find one quantity if other two quantities are given.

Mass (kg)	Volume (m3)	Density (kg/m3)
350	175	2
760	190	4

 
We know, $\mathrm{Relative} \mathrm{density} \mathrm{of} \mathrm{substance}=\frac{\mathrm{Density} \mathrm{of} \mathrm{substance}}{\mathrm{Density} \mathrm{of} \mathrm{water}}$
So, using above formula, we can find one quantity if other two quantities are given.

Density of Metal (kg/m3)	Density of water (kg/m3)	Relative Density
5$\times$103	103	5
8.5$\times$103	103	8.5

We know, $\mathrm{Pressure}=\frac{\mathrm{Force}}{\mathrm{Area}}$
So, using above formula, we can find one quantity if other two quantities are given. 

Weight (N)	Area (m2)	Pressure (N m−2)
800	0.04	20,000
1500	500	3

Page No 22:

Question 6:

The density of a metal is $10.8\times {10}^{3 }\mathrm{kg}/{\mathrm{m}}^3$. Find the relative density of the metal.

ANSWER:

Given:
Density of metal = $10.8\times {10}^{3 }\mathrm{kg}/{\mathrm{m}}^3$
We know, density of water = 1000 kg/m³
$\mathrm{Relative} \mathrm{density} \mathrm{of} \mathrm{substance} =\frac{\mathrm{Density} \mathrm{of} \mathrm{substance}}{\mathrm{Density} \mathrm{of} \mathrm{water}}$
$\mathrm{Relative} \mathrm{density} \mathrm{of} \mathrm{substance} =\frac{10.8\times {10}^3}{1000}=10.8$

Page No 22:

Question 7:

Volume of an object is 20 cm³ and the mass in 50 g. Density of water is 1 g cm^$-$3. Will the object float on water or sink in water?

ANSWER:

Given:
Volume of object = 20 cm³
Mass of object = 50 g
Density of object = $\frac{\mathrm{Mass} \mathrm{of} \mathrm{object}}{\mathrm{Volume} \mathrm{of} \mathrm{object}}=\frac{50}{20}=2.5 \mathrm{g}/{\mathrm{cm}}^3$
Now, we know density of water = 1 g/cm³
Since, density of object > density of water, therefore the object is going to sink in water.

Page No 22:

Question 8:

The volume of a plastic covered sealed box is 350 cm³ and the box has a mass 500 g. Will the box float on water or sink in water? what will be the mass of water displaced by the box?

ANSWER:

Given:
Volume of box = 350 cm³
Mass of box = 500 g
Density of object = $\frac{\mathrm{Mass} \mathrm{of} \mathrm{object}}{\mathrm{Volume} \mathrm{of} \mathrm{object}}=\frac{500}{350}=1.43 \mathrm{g}/{\mathrm{cm}}^3$
Now, we know density of water = 1 g/cm³
Since, density of box > density of water, therefore the object is going to sink in water.
Now, volume of liquid displaced = Volume of the object = 350 cm^{3
$$\begin{gathered} \Rightarrow \frac{\mathrm{Mass} \mathrm{of} \mathrm{liquid} \mathrm{displaced}}{\mathrm{Density} \mathrm{of} \mathrm{liquid} \mathrm{displaced}}= 350 {\mathrm{cm}}^3 \\ \Rightarrow \mathrm{Mass} \mathrm{of} \mathrm{liquid}=350\times 1=350 \mathrm{g} \end{gathered}$$} 

Elements, Compound and Mixtures (Std. 7)

Question 1:

Who are my companions ?

Group 'A'                       Group 'B'
 
1. Stainless steel          (a) Non-metal
2. Silver                       (b) compound 
3. Bhajini​ mixture       (c) Mixture 
   for milling
4. Salt                          (d) Element 
5. Coal                         (e) Alloy
6. Hydrogen                 (f) Metal

ANSWER:

Group 'A'                       Group 'B'
 
1. Stainless steel          (e) Alloy
2. Silver                       (f) Metal 
3. Bhajini​ mixture       (c) Mixture 
   for milling
4. Salt                         (b) compound 
5. Coal                        (a) Non-metal
6. Hydrogen               (d) Element 

Page No 99:

Question 2:

Write the names of elements from the following symbols :
Zn , Cd, Xe, Br, Ti, Cu, Fe, Si, Ir, Pt.

ANSWER:

Zn- Zinc
Cd- Cadmium
Xe- Xenon
Br- Barium
Ti- Titanium
Cu- Copper
Fe- Iron
Si- Silicon
Ir- Iridium
Pt- Platinum

Page No 99:

Question 3:

What are the molecular formulae of the following compounds ?
Hydrochloric acid, sulphuric acid, sodium chloride , glucose, methane.

ANSWER:

Hydrochloric acid- HCl
Sulphuric acid- H₂SO₄
Sodium chloride- NaCl
Glucose- C₆H₁₂O₆
Methane- CH₄

Page No 99:

Question 4:

Give scientific reasons.

(a) Buttermilk is churned to get butter .

(b) In chromatography, the ingredients of a mixture rise up to a limited height water rises up to upper end of the paper .

(c) A wet cloth is wrapped around a water storage container in summer .
 

ANSWER:

a. Butter milk has two components- water and fat/cream. Churning helps in the separation of these two components. The fat/cream collects on the top as a result of churning while the remaining part is left behind as liquid. 


b. Chromatography is a separation technique used to separate the different components in a liquid mixture. Separation of substances by chromatography is based on two properties of the substance:

• solubility of the substance in the solvent that moves up
• ability of the substance to stick to the stationary filter paper

These properties are different for different substances and are mutuall opposite to each other. It is the reason why all the components of the mixture rise upto a limited height when water rises up to the upper end of the paper.        


c. A wet cloth is wrapped around water containers in summers to keep the container and the water inside it cools. The water present in the cloth evapourates and along with that water the heat also evapourates thus keeping the container and water cool.

Page No 99:

Question 5:

Explain the difference .

(a) Metals and non-metals
(b) Mixture and compounds
(c) Atoms and molecules
(d) Separation by distillation and by separating funnel 

ANSWER:

a.

Physical properties	Metals	Non-metals
Malleability and ductility	They can be beaten into sheets and wires	They cannot form sheets or wires
Sonority	Metals are sonorous, they produce a ringing sound on beating	They are non−sonorous
Conduction	They conduct heat and electricity	Non-metals do not allow heat and electricity to pass through them
Chemical Properties
Nature of oxides	Metallic oxides are basic in nature	Oxides of non−metals are acidic
Reaction with water	Metals react with water	Non−metals do not react with water
Reaction with acids	Metals react with acids to produce hydrogen gas	They generally do not react with acids

b. 

	Mixture		Compound
1.	1It is obtained by the physical combination of any two substances.	1.	It is formed when two or more substances chemically combine in a fixed ratio.
2.	The composition of the constituents present in a mixture is not fixed.	2.	The composition of elements present in a compound is fixed.
3.	It displays the properties of all its constituents.	3.	It may or may not show the properties of its constituent elements.
4.	The constituents of a mixture can be separated using physical methods.	4.	The constituent elements of a compound can be separated only by using chemical methods.
5.	No change of energy is involved during the formation of a mixture.	5.	Change of energy is involved during the formation of a compound.

c. 

	Atoms		Molecules
(i)	Atoms are the smallest particles of an element that can take part in a chemical reaction.	(i)	Molecules are the smallest parts of an element or compound, which exist independently.
(ii)	They do not break up during chemical reactions.	(ii)	They break up during chemical reactions.
(iii)	They may or may not exist in free state.	(iii)	They exist in free forms.

d.

Separation by distillation	Separation by separating funnel
1. This method is employed for separation of two miscible liquids.	This method is employed for separation of two immiscible liquids.
2. It is based on the difference in the boiling points of two liquids.	It is based on the difference in the densities of the two liquids.

Page No 99:

Question 6:

Write answer to the following question in your own words.

(a)  How are the components of mixtures separated by simple methods ?
(b) Which elements ( metals and non-metals), compounds and mixtures do we use in our day-to-day life?
(c) In everyday life, where and for what purpose do we use centrifugation?
(d) Where are the methods of separation by distillation and by separating funnel used ? Why ?
(e) Which precaution will you take  while using the methods of distillation and separation by separating funnel ?

ANSWER:

a. The components of mixtures are separated by simple methods like:

Distillation: Distillataion and separating funnels are used in separation of liquid mixtures. Distillation is a method which is used for separating two miscible liquids. It is based on the difference in the boiling points of two liquids. Distillation can either be simple or fractional. Simple distillation can be used for liquids which have huge difference in their boiling points whereas fractional distillation is used in case of liquids which have close boiling points. Distillation can be used in the production of gasoline, distilled water, xylene, alcohol, paraffin, kerosene apart from separating mixtures.​

Separating funnels: Separation using separating funnels is used in case of immiscible liquids. It is based on the difference in the density of the two liquids. It can be used in separation of oil from water etc, two different types of immiscible oils etc.

Chromatography: It can be used to separate the coloured components of a mixture on the basis of the difference in the speeds of the components on chromatograph paper, when dissolved in the same solvent. The adsorbent paper acts as the stationary phase; it carries the components of the mixture on the paper. The mixture acts as the mobile phase and the components get separated. The component which moves slowly (i.e., the less-soluble component) appears as a spot on the lower side of the paper. The component which moves faster (i.e., the more-soluble component) appears as a dot on the higher side of the paper.

Centrifugation: Centrifugation is the process where a mixture is separated through spinning. It is used to separate skim milk from whole milk, water from your clothes, and blood cells from the blood plasma. 

b. Examples of mixtures we use in our daily life are- lemon and water, sugar and milk, salt and water, cereal and milk, cement, air, etc.
Examples of compounds we use in our daily life are- salt (NaCl), sugar (C₁₂H₂₂O₁₁), baking powder (NaHCO₃), vinegar (CH₃COOH), ethanol etc.
Examples of elements we use in our daily life are- aluminium, copper, iron, silver, gold etc.


c. We use centrifugation for the following purposes in our daily lives:

• Drying of wet clothes in the spin tub of a washing machine
• Extraction of DNA for forensic and experimental purposes
• Separation of blood components in medical science
• Working of roller coasters in amusement park
• Removing water from wet lettuce in salad spinner

d. Distillataion and separating funnels are used in separation of liquid mixtures. Distillation is a method which is used for separating two miscible liquids. It is based on the difference in the boiling points of two liquids. Distillation can either be simple or fractional. Simple distillation can be used for liquids which have huge difference in their boiling points whereas fractional distillation is used in case of liquids which have close boiling points. Distillation can be used in the production of gasoline, distilled water, xylene, alcohol, paraffin, kerosene apart from separating mixtures.

Separation using separating funnels is used in case of immiscible liquids. It is based on the difference in the density of the two liquids. It can be used in separation of oil from water etc, two different types of immiscible oils etc.


e. Precautions to be used during disitillation:

• The apparatus should be set in a proper manner with all the components fitted well.
• Never heat the system that is totally closed from the outside atmosphere to prevent explosion.
• Add boiling chips to reduce bumping (rapid boiling causing the liquid to expel out of the container).
• Control the rate of heating so not to overheat to avoid bumping.

Precautions to be used while using separating funnel for separation:

• The funnel should be tightly fixed to the stand in an errect position.
• The liquid in the funnel should be left undisturbed to allow it to separate.
• The stopper should be removed carefully without disturbing the setup.

Muscular system

Question 1:

Fill in the blanks with the right word from the brackets.
(a) The process of digestion starts from the ............. . (stomach / mouth)
(b) Eyelids have ............. muscles (voluntary / involuntary)
(c) ............ is not a function of the muscular system. (production of blood cells / Performing movements)
(d) Muscles of the heart are .............. (ordinary muscles / cardiac muscles)
(e) Pushing forward the food that has been chewed is the function of the ............. . (stomach / oesophagus).

ANSWER:

(a) The process of digestion starts from the mouth.
(b) Eyelids have voluntary muscles.
(c) Production of blood cells is not a function of the muscular system. 
(d) Muscles of the heart are cardiac muscles.
(e) Pushing forward the food that has been chewed is the function of the oesophagus.​
 

Page No 87:

Question 2:

Find a match for me.

Group 'A'	Group 'B'
(1) Cardiac muscles	(a) always function
(2) Are brought about by muscles	(b) we never feel tired.
(3) Pepsin	(c) uncontrolled and painful contraction of muscles.
(4) Cramps	(d) chewing movements of jaws.
(5) Skeletal muscles	(e) enzyme of the gastric juice.

ANSWER:

​

Group 'A'	Group 'B'
(1) Cardiac muscles	(b) we never feel tired.
(2) Are brought about by muscles	(d) chewing movements of jaws.
(3) Pepsin	(e) enzyme of the gastric juice.
(4) Cramps	(c) uncontrolled and painful contraction of muscles.
(5) Skeletal muscles	(a) always function

Page No 87:

Question 3:

Who is telling a lie ?

Organ	Statement
1. Tongue	My taste-buds can tell only a sweet taste.
2. Liver	I am the largest gland in the body.
3. Large intestine	I am 7.5 meter long.
4. Appendix	Digestion is impossible without me.
5. Lung	I play an important role in excretion.

ANSWER:

The tongue, large intestine, appendix and lungs are lying.

1. Tongue can taste salt, sweet and bitter tastes.
2. Large intestine is 1.5 meter long.
3. Appendix is not required for digestion.
4. Kidneys play an important role in excretion.

Page No 87:

Question 4:

Give reasons.
(1) Food becomes acidic in the stomach.
(2) Cardiac muscles are said to be involuntary muscles.
(3) Intoxicating substances should not be consumed.
(4) Your muscles should be strong and efficient.

ANSWER:

a. Food becomes acidic in stomach because of the presence of hydrochloric acid in the stomach. As the food reaches the stomach, it gets mixed with the hydrochloric acid present there. The hydrochloric acid plays the following roles in digestion:

1. It initiates protein digestion by activating the conversion of pepsinogen to pepsin.

2. It provides acidic medium for the activity of pepsin and other enzymes present in gastric juice.

b. Cardiac muscles are said to be involuntary because they are not controlled by our will. These muscles are found in heart and are the only muscles which work throughout the life without getting tired or fatigue.

c. Intoxicating substances should not be consumed because they harm the body directly or indirectly. Substances such as alcohol cause damage to the nervous system and the digestive system as well. Liver is the main organ which is affected by alcohol. Tobacco is one of the leading causes of oral cancer. Smoking has a direct effect on the respiratory system of an individual and can lead to lung cancer as well.

d. Our muscles should be strong and efficient because they carry out various vital functions in our body. From helping us to breath, digest food to helping us in walking and lifting weights, muscles play an important role. If our muscles are not strong enough we would get tired easily and feel fatigue. It is required to keep them in a healthy state by regular exercising and taking proper diet. 

Page No 87:

Question 5:

Answer the following.
(a) How many types of muscles are there? Which are those types?
(b) What causes the problem of acidity? What is its effect on the body?
(c) Name the different types of teeth. What is the function of each type?

ANSWER:

a. There are 3 types of muscles:

• Skeletal muscle fibre: They are found attached to the skeletal bones and are voluntary. Skeletal muscle fibres are striated and are bundled together in a parallel manner by a sheath of tough connective tissues.

• Smooth muscle fibres: They are present in the walls of internal organs such as blood vessels, stomach, etc., and are involuntary. Smooth muscle fibres are fusiform (taper at both ends) and non- striated. They are held together by cell junctions and are bundled together in a sheath of connective tissues.

• Cardiac muscle fibres: This is the only type of muscle present in the heart. They are contractile in nature and are involuntary. Plasma membranes of cardiac cells are fused together by cell junctions, and hence, the cells stick together. Communication junctions present as intercalated discs facilitate the contraction of cardiac cells as a unit.

b. Stomach contains special cells called oxyntic or parietal cells which secrete hydrochloric acid in stomach. It plays two important roles like:

1. It initiates protein digestion by activating the conversion of pepsinogen to pepsin.

2. It provides acidic medium for the activity of pepsin and other enzymes present in gastric juice.

However, if the level of this HCl exceeds its normal levels, it results in acidity/acid reflux. Higher levels of HCl can result in the following effects on the body:

1. burning sensation in the stomach
2. burning sensation in the throat and heart
3. difficulty in swallowing
4. regurgitation
5. restlessness
6. belching
7. nausea
8. prolonged sour taste in the mouth
9. indigestion

Exposure to higher levels of HCl for longer durations can also result in the development of peptic ulcers/ulcers in the stomach. 


c. There are 4 types of teeth which are found in humans:

1. Incisors are the teeth present at the front portion of the mouth. There are four incisors in each jaw. They are used for biting and cutting food.
2. Canines are located next to the incisors. There are two canines in each jaw. They are used for tearing and piercing food.
3. Premolars lie next to the canines. There are four premolars in each jaw. They are used for chewing and grinding food.
4. Molars lie next to the premolars at the end of the jaw. There are six molars in each jaw. They are also used for chewing and grinding food.

Page No 87:

Question 6:

Sketch and label a diagram of the digestive system and describe it in your own words.

ANSWER:

Major constituent organs of the human digestive system are: buccal cavity, oesophagus, stomach, small intestine, large intestine, rectum and anus.

Buccal cavity − It includes the teeth, saliva and tongue. The teeth break down the food. Digestion of food begins in the mouth. The tongue helps in the chewing and swallowing of food.

Oesophagus − The food passes from the mouth, down the oesophagus, into the stomach, as a result of the movement of the walls of the oesophagus.

Stomach − It mixes the food received from the oesophagus with digestive juices.

Small intestine − The food from the stomach moves into the small intestine, which receives intestinal juices from two glands − liver and pancreas. These juices help in the further digestion of food.

Large intestine − Water is absorbed in the large intestine.

Rectum and anus − Undigested food particles are thrown out with the help of the rectum and anus.

Std. 7.Sound

Question 1:

Fill in the blanks .

(a) Sound is generated by the rhythmic ............. of an object.

(b) The frequency of sound is measured in ............... .

(c) If ............. of sound is decreased , its loudness also decreases.

(d) A medium is necessary for .................... of sound.

ANSWER:

(a) Sound is generated by the rhythmic vibration of an object.

(b) The frequency of sound is measured in Hertz (Hz).

(c) If amplitude of sound is decreased, its loudness also decreases.

(d) A medium is necessary for propagation of sound.

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Question 2:

Match the pairs

Group 'A'                       Group 'B'

(a) Flute                         (1) Frequency less than 20 Hz

(b) Frequency                (2) Frequency more than 20000 Hz

(c) Sound level              (3) Vibrations in the air 

(d) Ultrasonic sound     (4) Measured in Hz

(e) Infrasonic sound      (5) Decibel

ANSWER:

Group 'A'	Group 'B'
(a) Flute	(3) Vibrations in the air
(b) Frequency	(4) Measured in Hz
(c) Sound level	(5) Decibel
(d) Ultrasonic sound	(2) Frequency more than 20000 Hz
(e) Infrasonic sound	(1) Frequency less than 20 Hz

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Question 3:

Give scientific reasons.

(a)  In earlier times, people used to listen for the arrival of a distant train by putting their ear to the rail.

(b) The sounds generated by a tabla and a sitar are different.

(c) If you were both on the moon , your friend will not be able to hear you call.

(d) We can hear the movement of a mosquito's wings but we cannot hear the movement of our hands.

ANSWER:

(a) In earlier times, people used to listen for the arrival of a distant train by putting their ear to the rail because they knew that sound travels faster through solids than gases. Thus, by putting their ear to the rails used to give them the idea of the arrival time of a train in advance.

(b) Due to difference in the pitch and timbre, the sound produced by a tabla and a sitar are different.

(c) We know that sound cannot travel through vacuum. Since there is no atmosphere on the moon atmosphere, so we cannot hear sound on the Moon. 

(d) The frequency of sound produced by the movement of mosquito's wings is in the audible range of humans whereas that produced by the movement of our hands falls in the inaudible range. Due to this reason, we can hear the movement of a mosquito's wings but cannot hear the movement of our hands.

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Question 4:

Write answers to the following questions .

(a) How is sound produced ?

(b) What does the intensity of sound depend upon ?

(c) Explain how the frequency of oscillation is related to the length of a pendulum and the amplitude of its oscillation.

(d) Explain the two ways by which the pitch of the sound generated by a stretched string can be changed.

ANSWER:

(a) The back and forth movement of an object produces sound. An object moving back and forth is said to be in vibration. Hence, sound is produced by vibrating objects.

(b) Intensity of sound depends on the amplitude of vibration of the sound. It is proportional to the square of amplitude of vibration of the sound.

(c) Frequency of oscillation of a pendulum decreases with increase in the length of the pendulum and vice-versa. It is independent of the amplitude of oscillation of pendulum provided the amplitude is small.

(d) Frequency or pitch of vibration of a stretched string can be changed by varying the

• tension in the string: If the string of the instrument is under high tension, then the pitch of the note produced on plucking the string will be high i.e. the note will be shriller because frequency of vibration of the string will be high.
• thickness of the string: If the string of the instrument is thin, then the pitch of the note produced on plucking the string will be high as frequency of vibration of the string will be high.