NCERT Solutions for Class 5 EVS Chapter 15

NCERT Solutions for Class 5 EVS Chapter 15 Blow Hot, Blow Cold in PDF file format free to use online or download. All the questions answers are updated for new academic session 2021-2022 CBSE and State Board students.

Extra questions with suitable explanation based on chapter 15 of grade 5 EVS are also given, which are quite helpful for the revision as well as tests and exam preparation.

NCERT Solutions for Class 5 EVS Chapter 15

Class 5 EVS Chapter 15 Question Answers Set 1

Why do we see drops of water on the bathroom mirror after a hot shower?

We see drops of water on the bathroom mirror after taking a hot shower because the water vapour rising from this water touches the cold surface of the bathroom mirror and condenses to form water droplets.

What happens when we breathe in air?

When we breathe in air, our chest expands as the air enters our lungs and takes space inside them.

How does exchange of gases take place in our body?

When we inhale or breathe in, the air enters our lungs and the oxygen present in the air moves from our lungs to our blood. At the same time, carbon dioxide, a waste gas, moves from our blood to the lungs and is exhaled or breathe out. This process is called gas exchange and is essential to life.

What happens when we breathe out the air?

When we breathe out the air then are chest contracts as we let the air go out of our blood by exhaling it.

Why do we spread out Khichdi on out plate before eating?

We spread out Khichdi on out plate before eating so as to increase the surface area thus allowing the vapour to escape quickly and it cools down our food.

Define Evaporation.

Evaporation is the process of changing the liquid(water) into water vapour (gas form) on heating.

Class 5 EVS Chapter 15 Question Answers Set 2

Why does a doctor use a stethoscope? Ans.

A doctor uses a stethoscope to listen to the sound of the heartbeat of the patient.

Why does a warm handkerchief give relief to a swollen forehead?

When we bang our head while playing and our forehead gets swollen and has redness then warm air is blown on a part of hanky to give relief from the pain or discomfort. Actually, on blowing, the scarf becomes a little warmer and gives some relief to the pain and swelling.

Why do we get breathless after jumping, running, dancing etc.?

During any physical work like running, walking faster, exercise etc. the body muscles need more energy, for which more oxygen is required to burn up the glucose to produce energy. Hence, we breathe faster to take in more oxygen to fulfil the energy needs or requirement by the muscles.

Why do we need we blow on our spectacles to wipe them clean?

We need to blow on our spectacles to wipe them clean because the air that we blow out of our mouth also has water vapour. When the vapours touch the cold surface(glass) of the spectacles, it condenses to form small droplets which we need to wipe from the surface to make it clean.

Why do we blow on lit damp wood or coal to help them burn faster?

When we blow on lit damp wood or coal, the unburnt carbon particles in the smoke move away thus making space for fresh air which is rich in oxygen that helps in burning of fire.

Gita cooled her soup by blowing on it whereas Vikas was blowing on his hands to keep them warm. How do you think blowing air helps in these two cases?

Gita’s soup was hotter as compared to the air she blew from her mouth. This helped her to cool her soup. Whereas the temperature outside was colder than Vikas’s breath which helped him to warm his hands. This is how blowing air helps.

Suggest different ways by which we can cool down soup or some hot liquid.
We can cool hot things by:

    • Stirring the liquid.
    • Pouring it from one container to another.
    • Pouring it in a bigger and wider vessel.
    • Placing the bowl in another container having cold water.

Class 5 EVS Chapter 15 Question Answers Set 3

What is condensation?

The process by which water vapour (gas form) changes into water(liquid) on cooling is called condensation.

Why do we breathe out clouds of mist from our mouth on a cold day?

When we breathe out, water vapour from our breath condenses as it comes in contact with the cold air of the atmosphere and mist is formed. So, the cold air causes the warm moisture in our breath to condense into tiny droplets of water that appear like a small, misty cloud.

How does our breath help to warm our hands in winter?

In winter, our hands become very cold. When we open our mouth wide and blow on to our hands there is warm, moist air inside our mouth. The steam of our breath then makes our hands warm in winter.

What is breathing?

Breathing is an activity that we do throughout our lives. We start breathing right from the moment, we are born and continue doing so till we die. It is a process that continues automatically. We breathe even when we are sleeping. Breathing is a natural process of inhaling oxygen and exhaling carbon dioxide. We breathe through our nose.

What happens to air when it becomes hot?

Air like most other substances, expands when heated. Warm air becomes lighter than cold air, and so when air is heated it rises. The air becomes less dense than the air surrounding it and also the distance between the molecules increases. So, the less dense air floats in the much denser air just like ice floats on water as ice is less dense than water.

Why does a hot air balloon fly?

Air becomes light on heating and there is more space between the molecules. As a result, the air becomes less dense than the surrounding matter and the hot air floats upward. That is why the hot air balloons fly in the sky.

What happens to the cold air?

When the air becomes cool, the temperature drops and the molecules move more slowly, taking up less room. The amount of space the air takes up reduces the air pressure. As a result, the air contracts when cooled. And it becomes heavier and comes down.

Why does a popcorn seller fans the burning coal while making popcorn?

We blow on a burning fire so that we keep it burning so as to increase the supply of oxygen which is important for burning. A popcorn seller therefore fans the burning coal to increase the supply of oxygen. Thus to increase the supply of air for making the popcorn, the popcorn seller fans them.

Why the air blown from our mouth cools the things in summer and warm in winters?

The air blown from our mouth is always at our normal body temperature which is 98.7⁰C. Therefore, when we blow at some colder thing in winter its temperature rises and if we blow at some hotter thing its temperature falls.

Class 5 EVS Chapter 15 Question Answers Set 4

Name the instruments that produce sound when we blow into them?

Been, brass band and flute are the instruments which produce sound when we blow them.

What do we do when there is some redness in your eyes?

We use the warmth of the breath to cure por reduce the redness of the eye or any injury, by blowing it onto the handkerchief and keeping it on the redness of the eye as it gives relief to us and reduces the pain.

How do instruments produce sound?

All musical instruments are able to create sound by causing matter to vibrate. The vibrations start the sound waves that move through the air. Most musical instruments use resonance or tone to amplify the sound waves and make the sounds louder. Resonance or the tone occurs when an object vibrates in response to sound waves of a certain frequency.

How does a flute produce sound?

A flute produces sound when a stream of air goes across a hole in the instrument and creates a vibration of air at the hole.

What does the movement of snake in clockwise and anti-clockwise direction tell us?

The movement of the snake in the clockwise direction means that the air is moving upwards. But when the snake is moving in anticlockwise direction, it means the air is moving downwards.

Why do we blow on hot potatoes?

The air that is coming out of the mouth is colder as compared to that of the hot potatoes. So, the air from the mouth cools down the hot potatoes. We blow on some food to cool them or we leave them as it is uncovered to let them cool down in the surrounding atmosphere
We also put some hot food in refrigerator also to cool them.

What is the correct way of breathing?
The correct ways of breathing are:
• Always breathe in air through the nose not from the mouth.
• Never sleep with your face covered because the same air you are inhaling again and again.
• Practice yoga and Pranayama. This helps in reducing stress.

Class 5 EVS Chapter 15 Question Answers Set 5

Why does our heart beat faster after running?

When we run or jump the blood circulation increases in our body. Our heart has to do more work to pump the blood faster. Therefore, it beats faster.

How can we cool down our hot porridge?

We can cool down porridge by:
a. pouring it in an open bowl.
b. putting it under the fan.
c. blowing air from the mouth.

How does the mirror look hazy when we blow hard on it?

When we blow hard on the mirror, some water vapours also come out from our breath and fall on the mirror. This water vapours make the mirror hazy.

Why should we always breathe with nose, not with mouth?

We should breathe with our nose than with our mouth because breathing through your nose can help to filter out dust and allergies, boost our oxygen uptake, and dampen the air we breathe in. Breathing through Mouth can dry our mouth and increase our risk of bad breath and gum inflammation.

Why does coal burn further when we blow on it instead of dying out?

Burning of coal takes place in presence of oxygen and when we are blowing on it, we are providing it more oxygen therefore it does not die out but burns further.

Why does on a cold winter morning the mirror becomes cloudy when you blow on it?

The air blown from our mouth has moisture in it in the form of water vapours. Thus when we blow air on the mirror surface which is cooler, it allows the vapours to cool down and hence cloudy surface is formed.

Why is it important to breathe well?

All the systems in our body are dependent on oxygen. So, effective breathing is very important as it not only provides us with a greater sense of mental clarity, but also helps us sleep better, digest food more efficiently, improve our body’s immune response, and reduce stress levels.

What things do you blow air from your mouth?
We blow air from mouth to:
• Clean our spectacles,
• to whistle,
• to clean any dust particles,
• to play the flute.

Class 5 EVS Chapter 15 Question Answers Set 6

Give two examples of each of the situations given below: We blow air from our mouth to cool hot things and warm cold things.

Examples of when we blow to cool hot things: A cup of tea and hot food.
Examples; when we blow to warm cool things: Our hands in winter, a piece of cloth.

What happens when we blow on a burning candle?

When we blow air on a burning candle, we are actually removing the hot air around the flame. By doing so, we reduce its temperature below the flash point and thus the candle goes out.

When we blow hard from our mouth onto our hands. How is the air from our mouth as compared to the air around.?

When we blow hard from my mouth onto my hands; the air from the mouth is hotter as compared to the air around.

Why is the air you breathe out warm?

The air we exhale or breathe out is hot because it is maintained to our body temperature. Exhaled air is warmer than inhaled air because it is the same room temperature air which we have taken in. The air which we breathe out is the air in the lungs which is warmed by core body heat.

What is the main motive of chapter 13 of the NCERT book of EVS class 5th?

The chapter is showing the story of and woodcutter and via that story, he tried to make the children understand how blowing air could cause change the temperature of various things in our favor.
Because blowing air makes the cold thing warn as the air we blow is warmer than the temperature of other object and then when we blow air on a hotter object it cools it down because the air is cooler than the object we are blowing air to.

Do you find chapter 15 of class 5th EVS was fun to read?

The chapter showed the story of a woodcutter and the dwarf. The dwarf was confused by looking at the man and the strange actions that he performed during the wood cutting. Then couldn’t stop but to ask the strange ways and when the man explained he understood but didn’t know about the reason why the methods were effective.

Is there any activity that can be suggested to understand the effects of blowing air as per chapter 15th of 5th class EVS?

I think the best way to describe the effects of blowing air is with the activity given below: –
Activity – Try to blow slowly with your mouth wide open on your hands and you will have hot air.
Then try to blow fast with a mouth as little open as possible you will feel cold and then try to find out does this happened.