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Saturday, June 27, 2015

Learnwell science chapter Metals and Non metal Questions answer class 8

CBSE/NCERT_Metals and Non Metal Questions answer class 8
Very short answer questions

1. What is malleability?

Ans: Metal can be beaten into thin sheet. this properties oh metal is called malleability. Gold is the most malleable metal.

2. Name a metal exist in liquid state

Ans: Mercury is a metal that exist in liquid state at room temperature.

3. Which metal is the best conductor of electricity?

Ans: Silver

4. Name the metals ha highest melting pint.

Ans: Tungsten

5. Name the lightest metal

Ans: Lithium

6. Which is the only non metal that can conduct electricity?

Ans: Graphite

7. Name the two non metals that are lustrous

Ans : Graphite and iodine

8. What are allotropes?

Ans: Two or more form of same element which differ in properties. Diamond and graphite are two allotropes of carbon

Write true and false
1. Metals react with oxygen to form oxide: False

Metals react with oxygen to form metallic oxide

2. Magnesium and aluminium react quickly with oxygen: False

Sodium and potassium react quickly with oxygen so they are stored in kerosene oil

3. Metals react with water to form metal oxide: True

4. All metal react with bases: False

Most of the metals do not react with bases. Only Zinc, lead and aluminium only react with strong bases like NaOH and KOH

5. Non Metal react with air at room temperature: False

Non Metal reacts with air on heating

6. Non metal do not react with water: True

Name the metals and Non metal used for:
1. Filling electric bulb – Argon

2. Constructing bridge: - Iron

3. Making electric wire: - copper and aluminium

4. Making foil for wrapping food: - Aluminium

5. Making pencil leads: - Graphite

6. Making x-ray shield and bullets: - lead

7. Water purification: Chlorine

8. Filled in electric tube and glow sign: - Neon

9. Filled in gas balloon: - Helium

10. Preserve blood and other donated organ: - Nitrogen

Answer these question: 

1. Why are musical instrument and bell made up of metal?

Ans: Musical instrument and bell are made up of metal because metal produce ringing sound when struck by something.

2. Why are electric wire made up of copper?

Ans: Electric wire is made up of copper because copper is god conductors of electricity.

3. Why sodium and potassium stored in kerosene?

Ans: Sodium and potassium react quickly with oxygen at room temperature so they are stored in kerosene oil

4. Why is phosphorous stored under water?

Ans: phosphorous rapidly burn in air at room temperature so it is stored under water for safety.

5. Why silver and gold do not react with hydrochloric acid?

Ans: This is because silver and gold are less reactive than hydrogen.

6. Why is graphite  not used for making electric cable?

This is because graphite is a non metal that cannot drawn into wire.

For rest of the questions  visit: Metals and Non metal questions with solution

Sunday, May 10, 2015

Microorganisms friend and Foe class 8 Solved Questions answer

Q. Viruses are considered as being on the border line between living and non-living organisms,Why?
Ans: Viruses is nonliving out side living cells but grows and multiplies inside living cell so,viruses are considered as being on the border line between living and non-living organisms.The study of viruses is called Virology.

Questions: What does Sargasso Sea woe its name to?
Ans: Sargasso Sea woe its name to Sargassum, a particular sea weeds that grow abundantly in sea. Sailor avoids this sea as their boat stuck in the tangled mass of seaweeds.

Questions: What are the difference between the cell of bacteria and the cell of other living body?
Ans: The difference between the cell of bacteria and the cell of other living body are

(i) Cell wall is not made up of cell wall

(ii) Do not have nucleus

(iii)Does not have membrane bound organelles

Questions: Do red and brown algae have chlorophyll?
Ans: Yes, red and brown algae have pigment of colour which cover the colour of chlorophyll and make them appear red brown or yellowish

Questions: Name a protozoon which can photosynthesize?
Ans: Euglena contain chlorophyll and can photosynthesise, lack of cell wall

Questions: How do bacteria reproduce?
Ans: Bacteria reproduce by binary fission

Question: What are antibiotics? What precautions must be taken while taking antibiotics?
Answer: Antibioticsare medicines produced by certain micro­organisms to kill other diseasecausing micro­organisms. These medicines are commonly obtained from bacteria and fungi. Streptomycin, tetracycline, penicillin, etc. are common antibiotics.

Precautions to be taken while using antibiotics:

(i) Antibiotics should be taken under the supervision of a well qualified doctor.
(ii) Course (intake) of antibiotics should be completed as per the prescription given by the doctor.
(iii) Antibiotics should be taken in the right amount and at the right time. A wrong dose of antibiotics makes the drug ineffective. Also, excessive consumption of drugs may kill the useful bacteria present in our body.

Question: Why do bacteria classified under plants?
Ans: The cell of bacteria is covered by protective layer called cell wall. This is the reason because which bacteria classified under plants.
Sometime bacteria passing through adverse condition, they developed additional protective wall called cyst around them. The process of the formation of cyst is called encystment.

Question: Which protozoan exhibits both characteristics of plants and animals?
Ans: Euglena

Question: what are retroviruses?
Ans: viruses lack of cellular structure like cytoplasm and organelles. they only consist of DNA and RNA encompassed by a protein layer called capsid. viruses carring RNA are called retroviruses.

Question: what are chemosynthetic bacteria
Ans: Bacteria that obtain energy required for metabolic processes from exothermic oxidation of inorganic or simple organic compounds without the aid of light.

Question: what are viruses that infect bacteria

Ans: Bacteriophage is a virus that infects and replicates within a bacterium.

Question: Why is it difficult to prepared vaccine for diseases caused by viruses?
Ans: viruses are difficult to be grown in an artificial nutrient medium . Hence, it difficult to prepared vaccine for diseases caused by viruses.

Question: Why do some bacteria and fungi considered as natural purifier?
Ans: some bacteria and fungi decompose the dead organic matter and therefore called natural purifier

Question: Why are legumes plants considered important in crop rotation?
Rhizobium bacteria present in the root nodules of legumes plants fix the atmospheric nitrogen ad maintain the fertility of soil.

Usefull links by jsuniltutorialMicroorganisms- : 

  • Objective Questions 
  • Microorganisms- : Notes 
  • Microorganisms- : MCQ 's 
  • Microorganisms : Test Paper-1 
  • Microorganisms : Test Paper -2 
  • Basic science solved Questions 

Saturday, May 9, 2015

Heat and Temperature Basic science Class 7 solution

Solution of chapter Heat and Temperature Basic science Class 7

A. Answer these question in not more than 20 words
1. Give an example to show that heat is a form of energy?

Answer: When we heat a pan of water, the water boils and at its temperature rises. The energy for this rise in temperature comes from heat. This shows that heat is a form of energy.

2. What is temperature? Name the scale used to measure it?

Answer: Temperature of a body is the measure of the hotness or coldness of the body. Celsius and Fahrenheit are the scales used to measure temperature.

Thermometry is branch of physics which deals with the measurement of temperature.

3. If hotness and coldness of a body is relative, how do we measure its degree of hotness?
Answer: We measure the degree of hotness or coldness of a body by measuring its temperature and comparing with standard temperature scale.

4. Mention three things that heat causes in substance?
Answer: Following are the three changes that heat can cause in any substance:

(a) Heat can change the temperature of a substance.

(b) Heat can expand a substance.

(c) Heat can change the state of a substance.

5. How does heat travel in spoon from hot boiling soup
Answer: Heat travel through the spoon by conduction.

6. How is it that we hold a match while it is burning?
Answer: We can hold a match while it is burning because wood is a bad conductor of heat and does not transfer of heat through conduction hand

7. How does turning on heater in room make the whole room warm?
Answer : Heat from the heater transfers to the whole room through radiation that rises the temperature of the whole room.

8. How does heat from the sun reaches the earth?
Answer: Heat from the sun reaches the earth by the process of radiation

9. Mention one similarity between heat and light?
Answer: Heat and light, both are forms of energy and both travel in a straight line

10. When two bodies are in contact, heat flows from hotter to colder bodies. When does heat stop flowing?

Answer: The flow of heat from the hotter body to the colder body will stop when the temperatures of the two bodies become equal.

B.Answer these question in not more than 40 words
1. Distinguish between the Celsius and Fahrenheit scale

Answer:

Celsius Scale

The lower fixed point is 0°C.

The upper fix point is 100 C.

The fundamental interval is divided in 100 equal parts and each part is called 1°C (one degree Celsius).

It is introduced by Celsius, is usually used in scientific laboratories.

Fahrenheit Scale

The lower fixed point is 32F.

The upper fix point is 212 F.

The fundamental interval is divided into 180 equal divisions. Each division is called one degree Fahrenheit. (1°F).

It is suggested by Gabriel Fahrenheit, is usually used in clinical and meteorological purposes.

2. How does heat travel through water on heating?
Answer: Convection is a process through which heat travels through the water. When water is heated, the water became lighter. Hot water rises up. The cold water from the sides moves down towards the source of heat This water also gets hot and rises and water from the sides moves down. This process continues till the whole water gets heated. This mode of heat transfer is known as convection

3. what happen to the radiant heat when fall on the body? What does the absorption of radiant heat by a body depends on?

Answer: When radiant energy falls on an object, some of its part is absorbed by the object and some is reflected by the object.

Absorption of the radiant energy depends upon the following: (i) The colour of the object. (ii) Nature of the surface.

4. (a) Mention difference between transfer of heat by conduction and that of radiation?
    (b) Mention difference between transfer of heat by conduction and that of convection?

Answer :

(a) Conduction: Flow of heat through a medium occurs without the movement of the material.

Radiation: Flow of heat occurs without the help of any material medium.

(b) Conduction: Flow of heat through a medium occurs without the movement of the medium.

Convection: Flow of heat through a medium occurs with the movement of medium.

C. Answer these question in not more than 100 word
1. Explain how land and see breeze originated?

Answer: Sea takes longer to get heated than the land. So, the land is hotter than the sea during the day. The air in contact with the land becomes hot and rises and the cooler air above the sea moves towards the land to replace the hot air. This movement of air from sea towards the land is called sea breeze.

After sunset, the land cools faster than the sea. The air above the sea is warmer than the air above the land. Air above the sea rises and the cooler air above the land moves towards the sea. This is called land breeze.

2. How would you demonstrate to a friend that gases expand on heating?
Answer: The following experiment explains that a gas expands when it is heated: Take a balloon and a glass bottle. Fit the balloon to the mouth of a glass bottle. Place the bottle in a pan of water. Put the pan over a gas flame and heat it.

It is now seen that the balloon gets inflated as the air inside the bottle becomes warm and expands. Also when the bottle is cooled, the balloon gets deflated as the air inside the bottle gets cooler. This shows that gas expands when it is heated.

3. (a) Why does It is better to wear light shades in summer?

(b) Why do two thin sweaters feel warmer than one thick sweater?

(c) ) Why do handles of utensils are made up of plastic while their handle are made up of plastic?


Answer: (a) It is better to wear light shades in summer because light shades absorb less heat.

(b) Two thin sweaters feel warmer than one thick sweater because the air trapped between the two sweaters acts as an insulator of heat. It does not allow the heat from our body to escape easily.

(c) Handles of utensils are made up of plastic because plastic is a poor conductor of heat. Therefore, heat will not travel through the plastic and the handles will remain cool during cooking. This saves our hand from getting injured from the heat.

Metal on the other is a conductor of heat, which helps in transferring heat from the burner flame to the food and helps in cooking the food.

D. Choose the correct options
1.(a) does not require any medium

2. (b) some metals conduct heat better than others

3. (b) so that the level of mercury does not fall as soon as the thermometer is taken out of the mouth

4. (c) poor absorber and good reflector of heat

5. (b) good absorber and good emitter of heat

6. (d) evaporation

E. Say true and false
Answer :

1. True. Water boils at 212 F.

2. False. Clinical thermometer has kink in the capillary tube.

3. True. Liquid expands more than solid.

4. True. The heat from the sun reaches to the earth through radiation.

5. False. Solid is a good conductor of heat than liquid and gas.

6. True. Heat flows in convection by the movement of the substance.

7. False. Transfer of heat by radiation do not need contact between a hot and a cold body.

8. True. Air is a poor conductor of heat.

Monday, April 27, 2015

Learnwell science class 8 chapter force and pressure n Friction

High order thinking skill [HOTS Questions]

Learnwell science class 8

1. Why are women advised not to wear high heeled shoes?

Ans: High heeled shoes do not distribute weight of body over the surface of and therefore women may fall on the ground due to less grips on ground. This is why women are advised not to wear high heeled shoes.

2. It is more difficult to pull boat on the beach than on the water?

Ans: Liquid and gases exert lesser friction as compared to solid surfaces. Therefore, boat on the beach experience more friction than on the water. Thus, it is more difficult to pull boat on the beach than on the water.

3. How are you able to drink juice using a straw?

Ans: When we suck air from straw the air pressure in the straw decreases that is enough to pull the juice. Air pressure pull the juice to move up inside the straw into our mouth .

4. Why is the tip of sewing needle sharp?

Ans: The sharp tip of sewing needle sharp distributes force over less are so that more pressure created on the clothes. This makes work with needle easier.

5. Why are powder sprinkled on the carom board before playing?
Ans: Powder sprinkled on the carom board before playing to reduce friction between coins and surface of carom board.

6. Why does a woman apply soap solution on their hand to put on bangles?
Ans: A woman apply soap solution on their hand to reduce friction so that it became easier to put on bangles .

7. Does the shoes having spikes on their sole help in making better grip on ice?
Ans: Yes, spikes increase friction and help to have better grip on ice.

8. Will a match stick catch fire when it is rubbed against cemented wall?

Ans: Yes. A match stick catches fire when it is rubbed against cemented wall because force of friction raises the temperature of match stick head.

9. What would happen if there is no friction?

Ans: Friction is the force that opposes the motion of every object. So if there is no friction then, there would be nothing to stop a moving object, and it would continue to move forever

10. Machine parts are oiled occasionally?

Ans: Lubricant like oil and grease form layer between the two moving surfaces so that they cannot directly rub each other. This make the movement smoother.

Learnwell science class 8 chapter Synthetic fiber   View or Download

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