CBSE Class 7 Science Revision Worksheet Set C

Topic : Flow of Heat

Long Question/Answers-

Question 1: Explain how heat is conducted from the heated end of a rod to its cold end.
Answer: Heat is conducted from the heated end of a rod to its cold end through the effective vibration of its molecules. Molecules of the rod starts vibrating as heat is supplied to it. When one end of the rod heats up, the molecules of that end starts vibrating and colliding with the nearby molecules to make them unstable. These molecules further hit their neighbouring molecules to transfer the heat. In this way, heat is transferred from one end of the rod to its other end.

Question 2: With an example of each, explain the uses of good and bad conductors of heat.
Answer: Good conductors of heat are used where we want to transfer heat faster from one point to the other. For example, cooking utensils are made of metals like brass, steel and aluminium, which are good conductors of heat. Though silver and copper are best conductors of heat but not usually used in cooking utensils as they are expensive. Bad conductors of heat are used where we want to stop the heat from getting transferred or where we do not want the heat to be lost or gained from the surroundings. For example, handles of cooking utensils are made of wood or plastic, which are bad conductors of heat. Hence, the handles don't heat up during cooking, thereby allowing us to hold the utensils comfortably.

Question 3: Describe the process of convection of heat.
Answer: The process of transference of heat through a fluid (liquid or gas) is called convection. It can be observed that when water is heated, water near the flame gets hot and starts rising up. On the other hand, cold water moves down from the sides of the flask, towards the source of heat. Then, this water becomes hot and rises up. This process continues till all the water present in the flask gets heated. This process of heat transfer is called convection.

Question 4: Explain with the help of diagrams how sea and land breezes are set up.
Answer: During the day, land gets heated up faster than the sea. So, the air above the land becomes warmer and lighter and moves upward. The air above the sea, which is relatively cooler, rushes to take its place. This results in to sea breeze during the day.

During the night, the land cools faster than the sea. Therefore, the air above the land is cooler and denser, while the air above sea is warmer and lighter. The air above the sea will move upwards and the cooler air from the land will rush to take its place. This causes land breeze during the night.

Question 5: Black objects absorb more heat than white or polished ones. Give two daily uses of this principle.
Answer: The everyday uses of the principle that black objects absorb more heat than white or polished ones are as follows:
1) Cooking utensils have black-polished/black-painted outer surface to absorb more heat. This helps in cooking the food in less time. 2) During winters, we wear black or dark coloured clothes, as these can absorb more heat and keep us warm than the white or dull coloured ones.

Question 6: Black objects radiate more heat than white objects. Give two everyday uses of this principle.
Answer: Black objects radiate more heat than white objects. Two everyday uses of this principle are:
1. Refrigerator pipes are painted with a dull black colour so that they can radiate the heat to the surrounding and cool themselves down.
2. Hot plates are coloured black so that it can radiate more heat energy to serve its purpose efficiently.

Question 7: Draw a neat labelled diagram of a thermos flask. How does it prevent transfer of heat by conduction, convection or radiation?
Answer: Thermos flask consists of double glass or metal walls with a space in between them. Air is completely sucked out of this space, and after that the walls are sealed at the neck or at the bottom of the flask. This vacuum is created to prevent heat loss due to conduction and convection, as both these methods require a medium to transfer heat. Then, the walls are silvered. This silver polish prevents the heat loss through radiation, as heat from inside the flask is radiated back to it and the external heat is reflected back to the surrounding. Finally, the vessel is put inside a metallic case with a plastic or cork support on both sides so as to protect the glass from breaking. At last, the mouth of the vessel is closed by a stopper made from an insulating material like plastic or cork.

Question 8: Two test tubes full of water are heated-one from below and the other near the top. In which case will the water heat up faster and why?
Answer: The test tube which is heated from below will heat up faster. When we heat water from below, the molecules at the bottom of the water start heating and expanding due to which they become light and move upwards. On moving upwards, they transfer the heat energy to other molecules. After transferring their energy, they contract and return to the bottom again. This cycle continues till the entire water gets heated through the convection mode. If water is heated from above, the heated molecules at the top will change their state to form steam, as they can hardly transfer the heat energy to the bottom layer due to the convection current

The Global Edge School - Ahead Of the Learning Curve Page 1

I. Answer the following question in detail.

1. Where is bile produced? What component of food does it digest?

2. Explain the digestion of food in ruminants?

3. What are the properties of a compound?

4. Differentiate between formula and symbol.

5. Write the formula of calcium carbonate showing the steps involved?

6. Balance the equation

Na + H₂O → NaOH + H₂

7. Define the following

a. Atomicity b. Valency c. Sericulture d. Radiation

8. What are factors that decide the quality of wool?

9. What are the effects of heat?

10. Explain the how heat causes expansion with the help of an experiment?

11. What precautions are used for using a clinical thermometer?

12. Explain the steps involved in the production of silk?

13. Why do woollen clothes keep us warm than cotton clothes?

14. Explain one natural phenomenon that occurs due to convection of current in air.

15. Write the symbols of following elements and radicals.

16. Magnesium b. Zinc c. Sulphate d. Copper e. Nitrate f. Phosphate.

17. Convert 350 C to 0F

18. How does the presence of acid in the stomach help?

19. Why room heaters have bright polished surface?

20. Why is mercury used as an indicator in a thermometer?

21. Write the function of different types of teeth?

22. Why are two thin woollen blankets warmer than a thick woollen blanket? 23. What are the factors that affect the soil formation? 24. Neela took 50ml of water in a measuring jar. She started pouring it over 50g of soil taken in a funnel. Soon the water started dripping from the funnel. 11ml of water was left in the measuring cylinder. What was the percentage of water retained by the soil?

The Global Edge School Revision Worksheet 2012-13

The Global Edge School - Ahead Of the Learning Curve Page 2

II. Fill in the blanks using appropriate answers.

1. The inner wall of the small intestine has fingerlike projection called _______________

2. Amoeba ingest its food with the help of __________________

3. The animal that lives on liquid food ________________

4. The wave like action that helps the muscles to push down the food ____________

5. The hydrochloric acid in the stomach helps in the digestion of _____________________

6. The partially digested food in rumiants is known as _______________

7. ______________ is made up of elements combined together in a fixed ratio

8. The formula of potassium is _______________

9. The elements present in a molecule of water is __________________ and _____________

10. The atom an of element that can exist independently is known as __________________

11. The formula of Magnesium sulphate is ______________

12. The complex compound that form animal fibre is _______________

13. Heat causes increase in _________________

14. The temperature at which the Celsius and Fahrenheit scale is the same ________________

15. The temperature scale used for scientific purpose _________________

16. The temperature range in the Fahrenheit clinical thermometer_________________

17. The heat of the sun reaches us by _______________________

18. The combining capacity of an element is its ____________________.

19. The transfer of heat in liquids is by _______________

20. The vaccum present in the thermos flask helps to reduce the flow of heat by _________________

21. The thermometer used to measure the temperature of boiling water ______________

22. Decayed organic matter is turned into dark coloured material is called_____________

23. The water holding capacity is higher in _________________

24. Loamy soil is a mixture of _________________

25. Sorters disease is caused by____________________

Diagrams to practice :

Draw labeled diagrams of (i) Human digestive system (ii) Thermos Flask (iii) Life cycle of Moth (iv) Sea and land Breeze (v) Ingestion of food in amoeba and hydra.

SECTION –A

Q1. Fill in the blanks

1. In insects,exchange of gases takes place through ______________________.

2. Amarbel is an example of__________________.

3. Gills are the ______________ of the skin.

4. _________ breaks down the starch into sugar.

5. _____________ in tongue detects the taste of food.

SECTION-B

Q2. State TRUE and FALSE

1. Turmeric is a synthetic indicator.

2. Tooth decay is caused by the presence of a base.

3. Solutions which are neither acidic nor basic are called indicators.

4. When an ant bytes it injects formic acid into the skin.

5. All the changes are chemical.

SECTION-C

Q4. Answer the following questions.

1. What is time period?

2. What is odometer and speedometer?.

3. What is a simple pendulum?

4. A simple pendulum takes 32 seconds to complete 20 oscillations. Find the time period?

5. The distance between two stations is 500 kms. A train takes 2 hours to cover this distance. Calculate speed in meters per second?

Topic : Flow of Heat

Short Question/Answers-

Question 1: What conditions are necessary for transfer of heat from one body to another by conduction?
Answer : Conditions necessary for the transfer of heat from one body to the other through conduction are as follows:
1. The two objects must be in contact with each other.
2. The temperatures of both the objects must be different.

Question 2: Differentiate between good and bad conductors of heat.
Answer : Good conductors of heat
Materials that can easily conduct heat through them are good conductors of heat.
For example, iron, copper and silver
Bad conductors of heat
Materials that cannot conduct heat through them are insulators of heat or bad conductors of heat.
For example, glass, wood and plastic

Question 3: Why do woolen clothes keep us warmer in winters than cotton clothes?
Answer : Woollen fibre comprises spaces between them that traps the air. Since air is a bad conductor of heat, it will not allow the body heat to escape, thereby keeping the body warm in winters. However, in a cotton fibre, such spaces are absent; hence, it can not keep us warmer as compared to the woollen clothes.

Question 4: Why are ventilators in houses provided at the top of walls?
Answer : Ventilators are installed on the top most part of the walls because the air we breathe out is warmer and lighter, and moves upwards. This stale air escapes through the ventilators, and fresh and cooler air enters the room through the doors and windows to take its place.

Question 5: How does heat from the sun reach us? At what speed does this transfer of heat take place?
Answer : Heat from the Sun reaches us through the process of radiation. There is millions of miles of empty space between the Earth and the Sun; therefore, only through radiation can heat be transferred to the Earth from the Sun, as it does not require any medium. The radiant heat travels similar to the speed of light.

Question 6: What is the function of the polished curved surface at the back of the heating rod in a room heater?
Answer : The polished curved surface at the back of the heating rod in a room heater reflects the radiant heat from the heating rod. Thus, the radiant heat spreads across the room, thereby making the room warmer.

Topic : Heat and its  Effect

Question 1: List four effects that heat produces.
Answer : Four effects of heat are as follows:
1. Change in temperature - When water is heated, its temperature increases and it starts boiling.
2. Change in State - On boiling water, steam is evolved, i.e., the its liquid state changes to its gaseous state.
3. Expansion - While heating water, some of it overflows due to expansion, i.e., increase in volume.
4. Chemical change - When vegetables are boiled in water while cooking, they become soft and their taste changes. Thus, a chemical change occurs in the vegetables.

Question 2: What does a bimetallic strip consist of?
Answer : A bimetallic strip consists of two metal strips, one of iron and the other of brass, bolted together firmly. The two metals expand at different rate on heating. Brass expands more than iron on heating, thereby bending the bimetallic strip towards the iron strip. And, after returning to the room temperature, the strip straightens as before.

Question 3: A steel bridge expands in summer. What precautions are taken to make sure this expansion does not damage the bridge?
Answer : A steel bridge expands in the summers. One of its end is fixed and the other end is made to rest on rollers with enough space for expansion. This allows the bridge to expand easily without taking any damage.

Question 4: How are temperature and hotness of a body related?
Answer : Hotter the body, higher is its temperature. Hence, hotness of a body is directly proportional to its temperature.

Question 5: What do you mean by 'upper fixed point'?
Answer : Upper fixed point is the temperature at which pure water boils at the sea level. In the Celsius scale, the upper fixed point is 100oC, and in the Fahrenheit scale, it is 212oF.

Question 6: Why does a clinical thermometer have a kink in its stem?
Answer : As soon as the thermometer is taken out of our mouth, i.e., from a hotter region to a colder region, the mercury in it starts contracting and tends to flow back into the bulb. The kink in the stem prevents the mercury from falling back immediately, thereby giving us the accurate reading of our body temperature 

a. Label the parts A, B, C, D
b. What does the above diagram represent.
c. Write in one line the function of A,B, C and D in the above diagram.

2. Identify Who am I
a. I give red colour to blood
b. I am used to measure your heart beat.
c. I fight against germs, which enter your body.
d. I am the fluid part of the blood.

Topic : Heat and its Effect 

Long question/answers-

Question 1: Explain why a substance expands on heating.
Answer : When a substance is heated, its molecular movement increases. Due to this, the average distance between the molecules also increases, thereby increasing the volume of the substance, i.e., expanding the substance. However, the movement of molecules depends upon the state of matter. Solids have tightly packed molecules; hence, least movement of molecules takes place leading to minimal expansion. In liquids, the molecules are less tightly packed as compared to solids; hence, they expand more than solids. Molecules of gases have no bonding at all; therefore, gases expand the most among the three.

Question 2: Give one example where expansion on heating is put to good use. Explain the working with the help of a labelled diagram.
Answer : Automatic fire alarm is an example of expansion on heating, which is put to good use. The fire alarm works on the principle that different solids expand differently when heated. An automatic fire alarm consists of a bimetallic strip which have two different metals strips, iron and brass, bolted together firmly. Brass expands more than iron on heating. Therefore, when fire will reach this bimetallic strip, the brass will expand more thereby bending it towards the iron strip. Due to this bending of the strip, the circuit for the electric bell is completed and it starts ringing as the fire alarm. Once the strip cools down, it will return to its original shape, i.e., straighten up to break the circuit and stop the alarm.

Question 3: Explain why gases expand more than liquids and solids.
Answer : Gases comprise loosely packed molecules as compared to that of liquids and solids. Therefore, when the gases are heated, there is a huge vibration in their molecules, thereby increasing the average distance between them. In case of solids and liquids, there is a strong bonding between their molecules; therefore on heating, these molecules vibrate but less comparatively to gases where the bonding between molecules is almost nil. Hence, in solids and liquids, expansion will take place but less than gases.

Question 4: Explain with the help of a labelled diagram an experiment to show that liquids expand when heated.
Answer : Take a flask filled with a liquid up to its brim. Take a rubber cork with a hole in it and insert a glass tube in it. Now, fit the cork tightly on the mouth of the flask. You will notice that the the level of the liquid will rise in the tube. Note down the level in the tube and start heating the flask. Initially, the liquid level will drop, but after a few moments it will start rising. At first the liquid level will fall due to the expansion of the flask on heating; then when this heat reaches the liquid, it starts expanding. Only at this time you will notice that the level of liquid is rising in the tube. After cooling back the liquid to its normal temperature, the level will drop again.

Question 5: Expansion on heating can be a nuisance. Explain giving two examples.
Answer : Expansion due to heating can be a nuisance. This is explained below with the help of the following examples: 1. Railway tracks are made up of iron which expands during the summers. Hence, if no gap is left between two conjoined tracks, they will bend and result into serious accidents.

Question 6: What precautions will you take while measuring temperature with a laboratory thermometer? What extra precaution will you take while measuring body temperature with a clinical thermometer?
Answer : Precautions that should be taken while using a laboratory thermometer for measuring temperature are as follows:
• It should be properly washed before and after use.
• It should be kept upright while reading the temperature.
• Its bulb should be properly dipped into the liquid or perfectly touched to the surface of the material whose temperature is being measured.
• Its bulb should not touch the surface of the container in which the material or liquid has been placed.
• It should be handled with care, as it is made up of a glass tube.
Precautions that should be taken while using a clinical thermometer for measuring body temperature are as follows:
• Sterilise the thermometer using an antiseptic solution before and after its use.
• Ensure that the mercury level is below 35oC before measuring the temperature.
• Take the reading keeping the level of mercury along the line of sight.
• Avoid holding it by its bulb while reading the temperature.

Q1 - Fill in the blanks

(1) The weight of air acting on a surface causes…………………………………….

(2) Warm air is …………………………………………than cold air.

(3) Cyclones are know as ……………………………………………..in the American Continent.

(4) The centre of a cyclone is a cloudless, calm area called the----------------------

(5) High speed winds are accompanied by ………………………………………..air pressure.

Q2 - Solve the crossword given below with the help of the clues.

Across: 4. Wind flows from a region of high pressure to a region of … ……Pressure.

5. A violent, dark, funnel- shaped cloud of hot air caused by spinning.

8. Pressure exerted by air.

9. Cyclones are know as ……………in Japan and Philippines.

10. These winds carry a lot of moisture.

Down; 1, Violent storm with an intense spiral.

2. Moving air.

3. The envelope of air surrounding our earth.

6. A storm accompanied with lightning and thunder.

7. This is required to form clouds.

Q3 - Give at least two examples from your own daily experience to confirm that air exerts pressure.

Topic : Flow of Heat

Fill in the blanks:-

1. The heat is transferred from one place to another place by conduction, convection and radiation.

2. In solids heat is transferred by conduction.

3. All liquids are bad conductors of heat.

4. Materials which do not allow heat to be conducted through them are called insulators.

5. The primary mode of heat transfer in a liquid is convection.

6. Sea and land breezes are actually convection current.

7. In vacuum heat energy can travel by the process of radiation.

8. The fastest method of heat transfer is radiation.

9. The thermos flask minimizes transfer of heat by conduction, convection and radiation.

10. Heat is transferred from hot to cold body.

11. Molecular movement takes place during convection.

12. Heat from the sun reaches us by the process of radiation.

1. Name the organism which grows on bread and makes it appear greenish black. What type of reproduction takes place in it.

2. Complete the following sentences:-

a. The flowers which contain only the pistil or the stamens are called ______.

b. The process of fusion of male and female gamete is called______.

c. The transfer of pollen from anther to stigma of same flower is called ____.

d. The basic unit of time is ____.

e. Distances between two cities are measured in _____.

f. Combination of two or more cells is called_______.

g. The coil of wire in a bulb which gets heated on passing electric current through it is called___.

3. Convert 50 km/hr into m/s.

1. Collect the pictures of the following animals and paste them in your HW notebook. Write and explain how each one of them is adapted to suit their environment.(in maximum three lines).

a) Fish b)tiger c}giraffe

2. Give reason

a) Toucans have a long beak

b) Penguins live in a group and remain huddled together

3. Give the difference between weather and climate of a place.

4. Name the following

a. Instrument to measure the maximum and minimum temperature during a day.

b. Instrument to measure wind speed.

c. Instrument to measure the amount of rainfall.

1. Why does our earth appear blue from share?

2. Which day is celebrated as world water days?

3. What is an aquifer? How is water pumped out of an aquifer.

4. What is

a. a canopy b. the crown of tree

5. What are decomposers?

6. Explain why forests are called green lung?