The World of Changes Class 6 Notes Questions and Answers Basic Science Chapter 7 Kerala Syllabus

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Class 6 Basic Science Chapter 7 The World of Changes Question Answer Notes

Basic Science Class 6 Chapter 7 Question Answer Notes The World of Changes

The World of Changes Class 6 Questions and Answers Notes

Let’s Assess

Question 1.
Find the odd one out.
(a) Fire cracker bursts
(b) Bottle breaks
(c) String of kite breaks
(d) Electric wire breaks
Answer:
(a) Fire cracker bursts (Chemical change. Others are physical change)

Question 2.
Examine the following changes and write whether they are chemical change or physical change.
Answer:

Change	Chemical change/Physical change
Camphor burning	Chemical change
Copper vessel getting verdigrised	Chemical change
Cutting firewood .	Physical change
Fermentation of dosa batter	Chemical change
Melting of tar	Physical change
Towel absorbing water	Physical change
Sugar dissolving in water	Physical change
Fish getting spoiled	Chemical change
Green leaves turning yellow	Chemical change

Question 3.
You know that electrical energy is being used by converting it into different forms. Write down the names of the devices that utilize the following energy transformations.
Answer:
Electrical energy to heat energy:

• Electric heater
• Electric Iron
• Electric Kettle

Electrical energy to chemical energy:

• Battery charger
• Electrolysis apparatus
• Electroplating Equipment

Electrical Energy to sound energy:

• Loudspeaker
• Electric Bell
• Buzzer

Electrical energy to light energy:

• Electric bulb
• Tube light
• Television Screen

Question 4.
All changes that occur by absorbing heat are chemical changes. Is this statement correct? Why?
Answer:
No, the statement is incorrect.
A change that occurs by absorbing heat is called an endothermic process.
While many chemical changes (endothermic reactions) absorb heat, many physical changes also absorb heat without forming a new substance.
Endothermic Physical Change Examples: Melting of ice, boiling of water, and dissolving certain salts in water.

Basic Science Class 6 Chapter 7 Question Answer Kerala Syllabus

Question 1.
Observe the pictures given below. What changes do you notice in each pair?

Answer:
Jaggery: crumbles
Bean seed: Sprouts
Cloud: Rains

Question 2.
Observe your surroundings and find more examples for similar changes. Write them in your Science Diary.
Answer:
Mango: Ripens
Bread: Bakes
Milk: Curdles
Leaf: Decays / Decomposes
Wood: Bums

Question 3.
Observe some handicrafts made from wax and paper.

Aren’t you interested in making such handicrafts? Let’s do it:
Materials Required: Colour clay, colour paper, chart paper, beads, scissors, sketch pen
Using the materials provided, try to make the objects shown in the picture. Display them in the class.

Object	Material	Steps
Snake	Clay	Roll long green clay tube. Add bead eyes and a pink tongue.
Pumpkin	Clay	Form an orange baft. Press grooves. Add a brown stem and green vine.
Butterflies	Paper, Beads	Fan-fold rectangular paper. Pinch center, secure with wire/thread, and add a bead body.

(a) What changes have occurred to each of the materials you used?
Answer:

• Colour clay: Moulded, rafted and shaped.
• Colour paper: Cut, Folded and attached
• Chart paper: Cut, Folded.

(b) In the case of colour clay, was it the substance or its shape that changed?
Answer:
Shape

(c) What changes occurred when handicrafts were made using chart paper and colour paper?
Answer:
When handicrafts were made using chart paper and colour paper, the primary changes were in shape and size.

(d) Does the substance change in each case? Discuss.
Answer:
No, the substance does not change in any of these cases.

(e) Isn’t it the same substance that changed into different shapes in each of these situations?
Answer:
Yes, in all of these handicrafts, the substance remains the same, but its physical state, shape, or form is changed.

Question 4.
Examine the pictures given below.

(a) What change happens to the object in each situation?
Answer:

• A whole watermelon is cut into slices.
• A wooden log is shaped into a wooden chair.
• A whole glass bottle shatters into broken pieces.
• Two pieces of pipe are joined together by heating.

(b) Are all the changes shown in the pictures similar? Discuss.
Answer:
Yes, all the changes shown are similar. Only the physical properties such as shape, size, or arrangement are changed.

Question 5.
Haven’t you learnt the changes in the state of water in the previous class? Try to write them.
Answer:
Solid (Ice)
Liquid (Water)
Gas (Water Vapour)

Question 6.
Write the situations where nature and other living organisms make use of the change in the state of water.
Answer:

• Formation of rain
• Melting of Snow and Ice
• Evaporation for Cooling
• Freezing for Insulation

When the state of water changes, there is no change in water as a substance.

Question 7.
Aren’t ice and water vapour the two other states of water? Complete the illustration.

Answer:

Question 8.
Shape, size and state are the physical properties of substances. Consider the situations we have already discussed.

• Making various shapes using clay
• Making chair using wood
• Cutting watermelon into pieces .
• Converting water into ice
• Expanding plastic pipe by heating

(a) Didn’t the physical properties of the substance change in all these situations?
Answer:
Yes, the physical properties changed in all these situations:
Making various shapes using clay – Shape and size Making chair using wood – Shape and size Cutting watermelon into pieces – Shape qnd size Converting water into ice – State
Expanding plastic pipe by heating – Size

(b) Was any new substance formed?
Answer:
No, in none of these situations was any new substance formed.
Let’s enquire more situations where physical properties change without any change in the substance.

Question 9.
Candle is a solid, isn’t it? Cut a candle into small pieces. Now what change has occurred to the wax?
Isn’t the wax still in the same state?
Answer:
Change: The wax changed in size and shape.
State: The wax is still in the solid state.

Question 10.
Take a small piece of wax in a spoon and heat it. What change has occurred to the state of the wax?
Answer:
The wax changed from solid to liquid state.

Question 11.
Allow the molten wax to cool for a while. Now, what change has occurred in its state?
Answer:
The molten wax changed from liquid to solid state.

Question 12.
Aren’t the solid wax and the molten wax the same substance?
Answer:
Yes, the solid wax and the molten wax are the same substance (wax).

Question 13.
Did the change in wax result in the formation of a new substance? Did it become a new substance on cooling?
Answer:
No, these changes did not result in the formation of a new substance. It did not become a new substance on cooling; it just returned to its solid wax form.

Question 14.
Tabulate your observations.
Answer:

Item	Change	State
Cutting wax into pieces	Change in shape and size	Solid
Heating wax	Change in state	Liquid
Cooling molten wax	Change in state	Solid

Question 15.
Heat the wax in the spoon for a longer time. Do you see the wax there now?
Answer:
Observation: If you heat the wax for a very long time, or with a very hot flame, the wax might start to bum.
Result: When wax bums, it turns into gases and sometimes soot. So, you would no longer see the solid or liquid wax.

Question 16.
Where did the wax go? Discuss and write down the changes of state of wax on heating.
Answer:
When you heat wax in a spoon for a longer time, or when a candle bums:
1. Melting: The solid wax first turns into liquid wax due to heat. (Solid → Liquid)
2. Vaporisation: The liquid wax then turns into wax vapour (a gas) due to more heat. (Liquid → Gas)
3. Burning: This wax vapour then reacts with oxygen in the air (it bums). It changes into new substances like invisible carbon dioxide gas and water vapour. This is why it seems to disappear.
So, the wax first changes state from solid to liquid to gas, and then the gas undergoes a chemical change (burning) to become invisible products.

Question 17.
Let’s do another experiment to observe the changes of state of wax on heating.
Materials Required: Wax, boiling tube, test tube holder, cotton, lamp
Take a piece of wax in the boiling tube and heat it using the lamp as shown in the picture.

The mouth of the boiling tube should be closed with cotton. What change happens to the wax in this experiment? Observe.
Observation – The solid wax will first melt and turn into liquid wax.
(a) Heat the molten wax again. What happens?
Answer:
If heated further, the liquid wax will start to vaporise.

(b) Remove the boiling tube from the lamp and observe it after a short while. What do you see inside the boiling tube now?
Answer:
After removing from the lamp and cooling, the liquid wax will solidify again, turning back into solid wax at the bottom of the tube.

(c) Take out the cotton from the boiling tube and observe. Can’t you see traces of wax on the cotton and in the upper part of the boiling tube? Observe the sides as well. What is the reason for this?
Answer:
Yes, you will see traces of wax on the cotton and the cooler upper parts/sides of the boiling tube.
Reason: When the liquid wax was heated, it turned into wax vapour (gas). Since the tube was closed with cotton, this vapour could not escape easily. As the vapour rise and touched the cooler surfaces of the tube and the cotton, it cooled down and condensed (gas → liquid), and then solidified (liquid → solid), forming solid wax traces.

(d) Based on the indicators given below, analyse the change that occurred in each situation. Arrive at a conclusion. Record it in your Science Diary.
Indicators
In the experiment you conducted

• What was the state of the wax before heating? – The wax was in the solid state.
• What change occurred in its state when heated? – It underwent melting (Solid → Liquid).
• To which state did it change on heating further? – It changed to the gaseous state (wax vapor) (Liquid → Gas).
• To which state did the vapourised wax change on cooling? – The wax vapour changed back to the solid state (Gas → Liquid → Solid), forming traces on the cooler walls of the tube.
• Did the wax turn into a new substance when its state changed? – No, the wax did not turn into a new substance. Solid wax, liquid wax, and wax vapour are all chemically the same substance.
• Is the change that occurred to the wax permanent or temporary? – Temporary

Answer:
Conclusion – Only the state, shape, and size were altered, and the original substance (wax) was retained.

Question 18.
Observe the illustration of the change that occurred to wax. Fill in the missing parts.

Answer:

Question 19.
Discuss the changes that occurred when wax received heat energy. Record them in your Science Diary.
Answer:
On receiving heat energy, wax melts into a liquid state and on further heating, the molten wax will change into a vapour state. These changes are temporary. They solidify when the temperature drops below their freezing point, but they melt back into liquid on warming.

Question 20.
Similarly, illustrate the change of state of ice when heat is received and releases. Record it in your Science Diary.
Answer:

The change that occurs in ice is temporary. No new substance is formed when ice undergoes a change of state.

Question 21.
Haven’t you noticed that ghee, coconut oil etc., that we use at home get solidified? In which season do these get solidified? Are these changes temporary or permanent? Do these changes result in the formation of new substances? Discuss.
Answer:
Ghee, coconut oil, and similar substances get solidified primarily during the winter season.
So far we have discussed the changes in the physical properties of substances like size, shape and state. Such changes are physical changes. No new substances are formed through physical changes.

Question 22.
Find examples for Physical change and list them. Present them in the class.
Answer:
1. Changes in State
These changes are often caused by heating or cooling:

• Melting: A block of ice turns into water.
• Solidifying: Coconut oil or ghee turning solid in cold weather.
• Evaporating: Water turning into steam or vapour when heated.
• Condensing: Water vapour cooling and turning back into liquid (like dew or clouds).

2. Changes in Size, Shape, or Form

• Cutting: Cutting a watermelon into pieces or cutting a sheet of paper.
• Breaking: Shattering a glass bottle,
• Shaping: Making different shapes using clay or shaping wood to make a chair.
• Expansion/Contraction: Heating a plastic pipe causes it to expand (change size).
• Grinding: Crushing jaggery cubes into powdered jaggery (changes size and shape).
• Dissolving: Sugar dissolving in water (only changes form, the sugar is still sugar).

Physical Change Changes in the physical properties of substances such as size, shape, and state are called physical changes. Expanding, melting, breaking and tearing are physical changes. No new substances are formed due to these physical changes. In some physical changes energy is either absorbed or released.

Question 23.
What do we do with broken and unusable plastic items at home?
Answer:

• Making decorative items
• Giving them to the Haritha Karma Sena (Green Action Force)
• Donation for Practice or Art
• Home Organisation: Cut plastic bottles into containers for storing small items like screws, craft supplies, buttons, or pens

Question 24.
We have discussed the physical changes of wax, water, plastic etc. Find more examples of physical changes being used in life situations and write them in your Science Diary. Complete the table and present it in the class.
Answer:

Situation	Physical change
Grinding rice	Size decreases, becomes powdered.
Melting butter in a pan	State changes from solid to liquid
Sharpening a pencil	Shape and size change
Boiling water	State changes from liquid to gas
Dissolving salt in water	Salt changes state from solid to aqueous solution

Question 25.
Haven’t you seen paper and wood burning? What change does happen here? Compare it with physical change.
Answer:
When paper and wood bum, they change to ashes. Here, new substances are formed, and it is a permanent change. Physical changes only change the shape, size, or state of the original material.
When paper is cut to make new shapes, the substances in the pieces of paper and the paper do not change. The substance obtained after burning paper is not the same as the paper before burning. The ash obtained after burning the paper is a new substance.

Question 26.
What happens when firewood burns? Discuss.
Answer:

• The wood reacts with oxygen in the air.
• New substances are formed: ash, smoke/gas.
• A lot of heat and light energy are released.

Question 27.
Are the changes that occurred here permanent or temporary? Find more examples of permanent changes.
Answer:
The changes that occur when firewood, paper, or wood are burned are permanent (irreversible) changes.

• Cooking an Egg
• Rusting of Iron
• Souring of Milk
• Baking Cake Dough
• Digesting Food

Question 28.
Shall we do an experiment related to this?
Materials Required: Sugar, spoon, matchbox, candle, coconut leaf midrib, lamp

Take a little sugar in a spoon and heat it using the lamp. Observe the change in sugar. Take the molten sugar on a coconut leaf midrib and taste it. – Molten sugar will have a sweet taste.
(a) What happens on heating it further?
Answer:
It will melt again

(b) Does the colour of the sugar change?
Answer:
Yes, the colour turns brown.

(c) After cooling take this substance on another coconut leaf midrib and taste it.
Answer:
Caramelised taste

(d) Heat it again until it turns black. Take this substance on another coconut leaf midrib, cool it and taste. Is there a change in taste?
Answer:
The molten sugar turns black and thickens into a solid, brittle residue, and a bitter, burnt taste replaces its sweet taste.

(e) Is this a new substance?
Answer:
Yes, It is a new substance

(f) Tabulate the change that occurred to sugar at each stage.
Answer:

• Sugar is white, sweet, and crystalline.
• Charcoal is black, tasteless, and powdery/brittle.

(b) What is the reason for the change in taste?
Answer:
The change in taste (from sweet to tasteless/bitter) is because the sugar has chemically changed into different substances. Sugar molecules are no longer present.

(c) Cool the substance obtained. Does the new substance turn back into sugar? What are the characteristics of this change? Discuss. Record it in your Science Diary.
Answer:
No, the black substance does not turn back into sugar upon cooling.
Characteristics of this change:

• New substance formed: A completely new substance (charcoal/carbon) with different properties (colour, taste, form) is created.
• Irreversible: The change cannot be easily reversed to get the original sugar back.
• This is an example of a chemical change.

Conclusion: When sugar is heated to form charcoal, it undergoes a chemical change. A new substance with entirely different properties (like colour and taste) is formed, and this change cannot be easily reversed.

Question 30.
Materials Required: Matchbox, magnesium ribbon, sandpaper
Clean the magnesium ribbon by rubbing it with sandpaper. With the help of the teacher, burn it using a matchstick.
Find the changes and discuss.
Answer:

• Change: The magnesium ribbon bums with a bright white light and turns into a white powdery substance (ash).
• Discussion: This is a chemical change.
• The original substance (magnesium metal) has completely changed into a new substance (magnesium oxide,.the white powder).
• Light and heat are also given off.
• This change is irreversible; we cannot easily get the shiny magnesium ribbon back from the white powder.

New substances were formed in both the experiments you have done. They can’t be changed back into the original substances. Therefore, these changes are permanent changes. Such changes are chemical changes. In chemical changes also, energy is absorbed or released.

Question 31.
What are the characteristics of chemical changes? Discuss.
Answer:
Formation of a New Substance: This is the most important sign. The original substance is lost, and a new substance with entirely different chemical properties (like taste, smell, or chemical composition) is formed.

• Example: Burning wood turns into ash and smoke.
  Permanent: Chemical changes usually cannot be easily reversed. You cannot simply cool the new substance to get the original one back.
• Example: You cannot turn a cooked egg back into a raw egg.
  Energy Change: Chemical changes often involve the absorption or release of energy (heat, light, or sound).
• Example: When a firecracker explodes or wood bums, heat and light are released.

Chemical Change When a chemical change occurs, the chemical properties of the substance change and new substances are formed. Energy is usually absorbed or released when such a change occurs. Chemical changes are permanent changes.

Question 32.
You have understood the major differences between the changes that occurred on heating wax and sugar. Discuss and tabulate the differences between physical and chemical changes. Present them in the t class.
Answer:

Physical change	Chemical change
The physical properties of substance change	The physical and chemical properties of substance change
No new substance is formed.	A new substance is formed.
Usually reversible. (Temporary)	Usually irreversible (Permanent)
The chemical composition of the substance remains the same.	The chemical composition of the substance changes

Question 33.
Some chemical changes that occur in daily life are given below. Discuss them.

• Digestion of food
• Verdigris on copper vessels
• Rusting of iron
• Souring of curd
• Burning of sparklers
• Cooking food
• Colour change of sliced apple
• Decomposition of waste

Among these, there are chemical changes that are useful and not useful for us. Tabulate and present them in the class. Find more examples of chemical changes and write them in your Science Diary.
Answer:

Useful Chemical Changes	Not Useful Chemical Changes
Digestion of food	Verdigris on copper vessels
Souring of curd (to make yogurt)	Rusting of iron
Cooking food	Colour change of sliced apple
Decomposition of waste	Burning of sparklers (pollution).

More Examples:
Useful:

• Photosynthesis by plants (making food using sunlight).
• Making soap from oils.
• Fermentation (making bread, idlis, dosas).
• Making cement.

Not Useful:

• Fading of colours in clothes due to sunlight.
• Burning of plastics (releases harmful gases).
• Batteries are losing charge over time.

Question 34.
Can we control the chemical changes that are not useful to us? What do we usually do to prevent rusting of iron? Discuss.
Answer:
Yes, we can control chemical changes that are not useful to us.
Here are the usual methods used to prevent:
1. Greasing/Oiling:
Applying a layer of grease or oil to the iron surface. This forms a thin, waterproof physical barrier.

2. Painting:
Applying a coat of paint, which creates a durable protective layer that seals the iron from the air and water.

Question 35.
Haven’t you noticed that iron pans are usually greased with oil? Find other methods like this that are being used to control chemical changes. Write them down.
Answer:

• Galvanization: Coating the iron with a layer of zinc metal.
• Refrigeration: Using cold temperatures to slow down the chemical reactions that cause food to spoil.
• Preservatives: Adding substances like salt, sugar, or vinegar to food to inhibit the growth of microorganisms (which cause chemical changes).

Rust Rust is formed by the reaction of iron with the moisture and oxygen in the air. Rusting of iron objects can be controlled by greasing them with oil or by painting. By doing this, the contact of iron with air is prevented.

Question 36.
Spoilage of food items is due to the chemical changes caused by the action of bacteria. What is usually done at home to prevent this? Find out.
Answer:

• Storing in a refrigerator
• Boiling: Heating milk or water to high temperatures kills the bacteria that cause spoilage.
• Drying/Dehydration: Removing the moisture from food (e.g., sun-drying chillies, fish, or making pickles). Bacteria need water to grow and cause chemical reactions.
• Salting/Sugaring (Adding Preservatives): Adding large amounts of salt (e.g., to meat, fish, or pickles) or sugar (e.g., to jams and jellies) removes water from the bacteria, slowing down their chemical activity.
• Pickling (Using Vinegar): The acid in vinegar prevents the growth of many types of spoilage bacteria.
• Storing in Air-tight Containers: Sealing food items tightly limits the oxygen supply, which slows down chemical changes like oxidation and the growth of aerobic bacteria.

Question 37.
Let’s do some experiments using some substances available at home.
Materials to be kept in the Science Kit:
Vinegar, eggshell, baking soda, glass, spoon
(a) Crush the eggshell into small pieces. What kind of change is this? Put a few pieces of eggshell in a glass. Pour vinegar into it and observe the change. Discuss the changes taking place here.
Answer:
Change: The eggshell changes its size and shape.
Kind of Change: This is a physical change. The eggshell is still eggshell, just in smaller pieces. Observation: When vinegar is poured onto eggshell pieces, you will see bubbles forming. The eggshell might also slowly become softer or dissolve over time.

Discussion of Changes:

• The bubbles are a gas (carbon dioxide) being produced.
• This is happening because the vinegar (an acid) is reacting with the eggshell (which contains calcium carbonate).
• This is a chemical change because new substances are formed, and you cannot easily get the original eggshell back in its previous form.

(b) Take a little vinegar in a glass and add one spoon of baking soda to it. What happens? W hat type of change is this?
Answer:

• Observation: When baking soda is added to vinegar, there will be a lot of vigorous fizzing and bubbling.
• What happens: A gas is quickly produced, causing the fizzing.
• Type of Change: This is a chemical change. Vinegar (acetic acid) reacts with baking soda (sodium bicarbonate) to produce carbon dioxide gas, water, and sodium acetate. The production of a new gas is a clear sign of a chemical change.

Question 38.
Isn’t it fascinating to watch a lighted sparkler? What are the things that attract you?
Answer:

• Sound
• Light
• Heat
• Movement

We know that when a sparkler is lit a chemical change takes place.
When a sparkler is lit, forms of energy like sound, light and heat are produced. You know that sound, light and heat are forms of energy.

Question 39.
What is the reason for the energy change when a sparkler is lit?
Answer:
The reason for the energy change (production of sound, light, and heat) when a sparkler is lit is a chemical change happening very rapidly. The stored energy within the chemicals of the sparkler is released as light, heat, and sound when they chemically react and bum.

There are chemical substances in a sparkler. It contains chemical energy. Chemical energy is present not only in the substances present in a sparkler, but in all substances. When the sparkler is lit, the chemical » energy in the sparkler is converted into the forms of energy like sound, light and heat.

Question 40.
Which are the energy changes that happen when a sparkler is lit? Complete the illustration given below.

Answer:

Question 41.
Some chemical changes are given in the table. Discuss the energy changes taking place in them. Put a tick (✓) mark in the appropriate columns. Write the conclusions in the Science Diary.

Answer:

Question 42.
Observe the picture.

(a) What is the process taking place in plants?
Answer:
Photosynthesis

(b) Which substances are being used here?
Answer:
Sunlight, Carbon dioxide, Water

(c) Which form of energy do plants use during photosynthesis?
Answer:
Plants use light energy (front the sun) during photosynthesis.
During photosynthesis, light energy is converted into chemical energy in the food (glucose) that plants produce. The food that plants produce through photosynthesis is glucose. It contains chemical energy.

Photosynthesis Photosynthesis is the process by which plants produce food using water and carbon dioxide, in the presence of sunlight, with the help of chlorophyll.

Question 43.
You have understood that when plants produce food, light energy is stored as chemical energy. Does this chemical energy stored in plants reach other living organisms? How does this happen? Discuss.
Answer:
The chemical energy stored in plants reaches other living organisms through food chains.

• Plants (Producers) capture and store light energy as chemical energy (food).
• Herbivores (Primary Consumers) eat the plants, gaining the stored chemical energy.
• Carnivores (Secondary Consumers) eat the herbivores, transferring the energy further up the chain.

Question 44.
Haven’t you seen a mixer grinder working? Which energy is used to operate the mixer grinder?
Answer:
The energy used to operate a mixer grinder is Electrical energy.

Question 45.
Do any parts of the mixer grinder move? Which form of energy is required to move the machine parts?
Answer:
Yes, many parts of the mixer grinder move:

• The blades inside the jar spin very fast.
• The motor inside the base spins.

The form of energy required to move these machine parts is Mechanical energy. (The electrical energy is converted into mechanical energy to make the blades spin.)

Moving machine parts possess mechanical energy.

Question 46.
Sound is produced while the machine part of the mixer grinder works. Apart from the forms of energy discussed earlier, are there any other forms of energy produced here?
Answer:
Yes, apart from the electrical energy used and the mechanical energy produced to make the blades move, sound energy is definitely produced.

Question 47.
Switch off the mixer grinder and touch it. Is it warm?
Answer:
Yes, if the mixer grinder has been working for some time, it will feel warm (or even hot) to the touch. This means heat energy is also produced.
You have understood that when a mixer grinder works, electrical energy changes into various forms of energy.

Question 48.
What are the energy changes that occur when a mixer grinder works? Write them in the Science Diary.

Answer:
When a mixer grinder works, electrical energy is converted into mechanical energy, sound energy and heat energy.

Question 49.
Discuss the devices that convert electrical energy into mechanical energy and write them in the Science Diary.
Answer:

• Electric Fan
• Water Pump
• Washing Machine
• Drilling Machine
• Electric Car/Bike
• Hair Dryer

Question 50.
Observe the pictures given below. What energy transformations do we utilize in each device?

Answer:

Question 51.
Find more examples of utilising energy transformations and write them.
Answer:
Here are a few more examples of utilising energy transformations:

1. Torch/Flashlight: Chemical energy (in battery) → Electrical energy→ Light energy
2. Solar Cell/Panel: Light energy (from sun) → Electrical energy
3. Generator: Mechanical energy (turning turbine) → Electrical energy
4. Microwave Oven: Electrical energy → Heat energy (microwaves)
5. Firewood Burning: Chemical energy (in wood) → Heat energy → Light energy

Question 52.
The pictures below show three different types of bulbs we have used at different periods. The amount of light obtained in all three cases is almost the same.

Which of these do you use more in your house? Why? Analyse the energy transformations happening in each and find the reason.
Answer:
Most houses today use LED Bulbs more.
Reason: LED bulbs are the most energy-efficient among the three. They provide almost the same amount of light, using much less electrical energy and generating very little wasted heat.
We don’t utilise the heat energy produced along with light energy when a bulb glows. Unutilised heat energy is energy loss.

Question 53.
What is the advantage of reducing the use of filament bulbs and increasing the use of LED bulbs? What could be the reason for the promotion of LED bulbs by the electricity board? You must promote LED bulbs in your house too.
Answer:
The main advantage of using LED bulbs over filament bulbs is energy efficiency, leading to electricity savings. LED bulbs convert a much larger portion of electrical energy into useful light energy and waste very little as heat energy. Filament bulbs waste most energy as heat.
In many situations, one form of energy is transformed into multiple forms of energy .
Understood that we don’t use all these forms of energy.

Question 54.
Which forms of energy are produced in the following situations? Which form of energy among them is utilised? Which forms of energy are wasted? Complete the table, analyse and present it in the class.

Answer:

Situation	Form of energy produced	Form of energy utilized	Form of energy not utilized
Working of a water motor	Mechanical energy Fleat energy Sound energy	Mechanical energy	Heat energy Sound energy
Working of a fan	Mechanical energy, Heat energy, Sound energy	Mechanical energy	Heat energy Sound energy
Working of mixer grinder	Mechanical energy, Heat energy, Sound energy	Mechanical energy	Heat energy Sound energy

Knowledge about chemical change, physical change and energy change helps us to understand and explain the changes happening around us.
Use of devices that reduce energy loss in energy transformations make our lives better. This helps in energy conservation.

Class 6 Basic Science Chapter 7 Question Answer Extended Activities

Question 1.
Write examples of chemical and physical changes by observing the activities in the kitchen.
Answer:
Physical Changes

• Melting butter or chocolate.
• Boiling water.
• Dissolving sugar or salt
• Cutting vegetables/fruits
• Grinding spices Chemical Changes:
• Baking a cake or bread
• Caramelisation of sugar
• Browning of meat
• Cooking an egg
• Souring of milk
• Ripening of fruit

Question 2.
Find methods that reduce consumption of electricity and record them in your Science Diary.
Answer:
Electricity Reduction Methods

• Lighting: Replace incandescent bulbs with LED lighting.
• Phantom Load: Unplug unused electronics and appliances to eliminate “phantom load” (standby power), or use smart power strips.
• Heating and Cooling: Use smart or programmable thermostats to automatically adjust temperatures, and ensure your home is well insulated and air leaks are sealed.
• Appliances: Purchase appliances with a high Energy Star rating.
• Laundry: Wash clothes in cold water and air-dry laundry instead of using a dryer.
• Water Heating: Reduce hot water use by taking shorter showers and lowering the water heater temperature to 120°F.
• Cooking: Cook efficiently by using lids on pots, using smaller appliances (like a microwave or toaster oven), and avoiding frequently opening the oven door.
• Natural Light: Maximise the use of natural light during the day to reduce reliance on artificial lighting.

Question 3.
What are the methods that you would suggest to reduce energy loss in the following situations? Write your suggestions and present them in the class.
(a) Old fan makes more noise when it works.
(b) Wear and tear occur in the engine parts of vehicles.
(c) Fire escapes from the firewood stove.
Answer:
(a) Old Fan (Noise)
The noise indicates energy lost to friction (heat and sound).
Suggestion: Lubricate the motor bearings and clean/balance the blades.

(b) Vehicle Engine (Wear and Tear)
Wear increases energy loss through frictional heat and poor combustion.
Suggestion: Perform regular oil changes and maintenance (filters, spark plugs) to reduce friction and optimise burning.

(c) Firewood Stove (Escaping Fire)
Escaping heat wastes thermal energy and fuel.
Suggestion: Use an enclosed, high-efficiency stove and control air vents to direct heat to the pot and ensure complete fuel bum.

The World of Changes Notes Pdf

The World of Changes Class 6 Notes Kerala Syllabus

• Changes in the physical properties of substances such as size, shape, and state are called physical changes. Expanding, melting, breaking and tearing are physical changes. No new substances are formed due to these physical changes. In some physical changes energy is either absorbed or released.
• When plastic bums, poisonous gases harmful to living organisms are produced. Reusing and recycling plastic, instead of throwing it away or burning is an act of nature conservation. Protect nature by proper utilisation of physical changes.
• When a chemical change occurs, the chemical properties of the substance change and new substances are formed. Energy is usually absorbed or released when such a change occurs. Chemical changes are permanent changes.

Differences between Physical and Chemical changes

Physical change	Chemical change
The physical properties of substance change	The physical and chemical properties of substance change
No new substance is formed.	A new substance is formed.
Usually reversible. (Temporary)	Usually irreversible (Permanent)
The chemical composition of the substance remains the same.	The chemical composition of the substance changes

• Rust is formed by the reaction of iron with the moisture and oxygen in the air. Rusting of iron objects can be controlled by greasing them with oil or by painting. By doing this, the contact of iron with air is prevented.
• There are chemical substances in a sparkler. It contains chemical energy. Chemical energy is present not only in the substances present in a sparkler, but in all substances. When the sparkler is lit, the chemical energy in the sparkler is converted into the forms of energy like sound, light and heat.
• Photosynthesis is the process by which plants produce food using water and carbon dioxide, in the presence of sunlight, with the help of chlorophyll.
• Moving machine parts possess mechanical energy.

Introduction

The world is constantly changing. From a simple process like ice melting to a complex one like burning wood, matter continuously transforms. Understanding these transformations is key to understanding the materials and phenomena around us.

This chapter explores how substances change, focusing on three core concepts:

• Physical Change: Changes in the appearance or state of a substance, which are temporary and reversible. For example, when water freezes, it changes its state (liquid to solid), but it remains water.
• Chemical Change: Changes where a substance is converted into entirely new substances with different properties. These changes are usually permanent and involve a change in chemical composition. A classic example is when milk turns into curd.
• Energy Changes: All changes, whether physical or chemical, are accompanied by a transfer of energy. Some changes absorb energy from the surroundings (e.g., melting ice), while others release energy, often as heat or light (e.g., burning a cracker).

By studying these changes, you will learn to distinguish between a simple shift in form and a true transformation of matter, and to recognise the role of energy in every process.

The picture shows a cute chick. It was hatched from an egg. For an egg to hatch and become a chick, many changes must have occurred within the egg.

PHYSICAL CHANGES IN DAILY LIFE
Recycling
Plastic carry bags and other plastic items thrown around carelessly cause major environmental issues. Most of them can be recycled into new items. Metals like iron, brass and aluminium can also be recycled in this way.

Reuse
Haven’t you seen many items that are no longer useful, being used for other purposes? This is reuse. You can also make use of such un usable materials in various ways like this. Look at the examples given in the picture.

Let’s Protect Nature
When plastic bums, poisonous gases harmful to living organisms are produced. Reusing and recycling plastic, instead of throwing it away or burning is an act of nature conservation. Protect nature by proper utilisation of physical changes.

CHEMICAL CHANGE IN DAILY LIFE
Many chemical changes occur daily in nature. We make use of many of these changes in our daily lives. Shall we discuss such experiences?
How do you understand that a mango has ripened? – We can tell a mango has ripened by observing changes in its
physical properties:

• Colour: It changes from green to yellow, orange, or reddish.
• Softness: It becomes softer to the touch.
• Smell: It develops a sweet, distinct aroma.
• Taste: It changes from sour to sweet and juicy.

The ripening of a mango involves chemical changes.
How is milk converted to curd? – Milk is converted to curd through a process called curdling, which is a chemical change caused by bacteria. A chemical change occurs during curdling of milk also.

ENERGY CHANGE IN DAILY LIFE
Energy changes are used for various purposes in daily life.

ENERGY TRANSFORMATION AND ENERGY LOSS
When energy transformation occurs a lot of energy get wasted without being used.

• For an electric bulb, the main purpose is to produce light energy.
• However, a lot of heat energy is also generated. This heat is usually not useful and is considered wasted energy for lighting purposes.