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  • Smart Learning for All.

  • Topic: Tyndall Effect.

  • Why does the sky appear blue?

  • It is such a beautiful rainbow.

  • Have you ever wondered, how it is formed?

  • A rainbow is formed when raindrops split sunlight into different colors.

  • Sunlight or white light consists of many colors.

  • However, only a few of them are visible to us.

  • A band of these visible colors is called a visible spectrum.

  • When we see a rainbow, our brain and eyes distinguish the visible spectrum into seven main colors.

  • Namely red, orange, yellow, green, blue, indigo and violet.

  • Did you notice that the size of the balls increased?

  • Yes, you guessed right.

  • The balls represent the different colors of a rainbow in increasing order of their wavelengths.

  • Wavelength is the distance between consecutive crests or consecutive troughs in a wave.

  • In a rainbow, as we move from violet to red, the wavelength of colors increases.

  • Violet has the shortest wavelength while red has the longest wavelength.

  • Do you think that our eyes have a natural inclination towards blue as compared to violet?

  • Yes, this is one of the reasons why our sky appears blue and not violet.

  • To understand this, first let us study about Tyndall effect.

  • Tyndall effect is a phenomenon in which a beam of light scatters on striking the particles present in its path.

  • This scattering of light is responsible for the blue color of the sky.

  • We know that our atmosphere primarily consists of oxygen and nitrogen particles.

  • Along with dust, smoke and other particles in comparatively smaller proportions.

  • The size of these particles in the atmosphere is responsible for the color of scattered light.

  • When the sunlight strikes particles of dust,smoke, etc.

  • Which are bigger than the wavelength of sunlight, all the colors of sunlight are equally scattered.

  • As a result, the scattered light appears white.

  • However, when the sunlight strikes particles of oxygen and nitrogen.

  • Which are smaller than the wavelength of sunlight, the colors of sunlight having shorter wavelengths.

  • Blue and violet are much more scattered than colors having longer wavelengths.

  • But our eyes are much more sensitive to blue color as compared to violet, hence the sky appears blue to us.

  • Topic: Density.

  • Why does oil float on water?

  • Did you realize that a large log of wood floated on water but a comparatively smaller piece of rock sank?

  • How is this even possible?

  • This is possible because of density.

  • It is the measure of the mass of an object per unit volume.

  • In the first case, the log of wood floats on water because it has less density than water.

  • This means that the amount of mass present in unit volume of wood.

  • Is less than the amount of mass present in unit volume of water.

  • However, in the second case, the piece of rock sinks because it has more density than water.

  • This means that the amount of mass present in unit volume of rock.

  • Is more than the amount of mass present in unit volume of water.

  • Do you know why the helium filled balloon is rising up in the air?

  • This is again because of density.

  • The balloon consists of helium gas which has less density than the surrounding air, hence it rises up.

  • Here, have a look.

  • Oil is floating on water.

  • Are you assuming that this is because of density?

  • Yes, you are right.

  • Oil has less density than water.

  • Hence, it floats.

  • However, there is another reason due to which oil floats on water.

  • The reason is that both oil and water are immiscible liquids.

  • They do not mix with each other even if we shake them.

  • They separate out into two layers when kept undisturbed for sometime.

  • Topic: Centrifugation.

  • How is the principle of centrifugation helpful in blood banks?

  • Do you know that jelly is a colloidal solution?

  • A colloidal solution is a solution whose particles neither dissolve nor settle down.

  • Another example of a colloidal solution is blood.

  • Blood consists of various components like red blood cells, white blood cells, platelets, plasma, etc.

  • Which neither dissolve nor settle down.

  • Usually, in blood banks, when a blood sample needs to be tested, its components have to be separated.

  • So, how can we separate those components?

  • What do you think?

  • Can we use a filtration technique to separate various components of blood?

  • No, filtration is not useful because the size of the components of blood is so small.

  • That they can easily pass through the filter paper.

  • Similar to this merry go round.

  • A machine called centrifuge is used in blood banks to separate blood components.

  • In the centrifuge machine, a test tube filled with a blood sample is rotated at a constant high speed.

  • This process is called centrifugation.

  • Centrifugation is based on centripetal acceleration.

  • Due to centripetal acceleration, the heavier components, that is, the red blood cells move outwards.

  • The white blood cells and platelets which are lighter than red blood cells form the middle layer.

  • Plasma being the lightest moves towards the center.

  • In this way, components of blood get separated by the principle of centrifugation.

  • Topic: Balanced and Unbalanced Forces.

  • How are we able to stand on the earth without falling into the center of the earth?

  • Hey. That was a nice balancing act.

  • Do you know there are certain forces around us which keep us balanced or unbalanced?

  • Force is a push or a pull exerted on an object.

  • Every object on the earth experiences various forces.

  • When a number of forces acting on an object are such that their resultant force is zero.

  • Then the forces are said to be balanced.

  • Whereas, when a number of forces acting on an object are such that their resultant force is not equal to zero.

  • Then the forces are said to be unbalanced.

  • When he was falling which forces were acting on him?

  • Were they balanced or unbalanced?

  • In this case, unbalanced forces were acting on him.

  • On earth, many forces act on an object.

  • One of them is gravitational force of the earth.

  • Gravitational force of the earth is the force which pulls all the objects downwards.

  • Towards the center of the earth.

  • Let's get back to the question.

  • When he was falling, the gravitational force over powered all other forces.

  • So, the resultant force was not equal to zero.

  • We can conclude that unbalanced forces were acting on him.

  • Did you see that?

  • He landed safely.

  • But if the gravitational force was pulling him towards the center of the earth.

  • Why did he fall on the ground and not into the center of the earth?

  • We know that gravitational force is pulling us downwards.

  • However, there is another force exerted by the ground which pushes us upwards.

  • This force is called the normal force.

  • It is equal to the gravitational force.

  • Normal force is exerted by a surface only when we are in contact with it.

  • Since these two forces acting on us are equal but opposite to each other.

  • Their resultant, that is, net force is zero.

  • Thus, these balanced forces keep us from falling into the center of the earth.

  • Topic: Solubility.

  • When you open a shaken cold drink bottle, what makes the fizz explode out?

  • Did he really prepare a cold drink from flavored water and carbon dioxide?

  • Yes.

  • A cold drink usually contains flavored water and excess amount of carbon dioxide dissolved in it.

  • This mixture forms carbonic acid which gives the cold drink a distinctive flavor.

  • Under normal conditions, it is difficult to dissolve excess carbon dioxide in water.

  • Only a certain amount dissolves easily.

  • Hence, to obtain that distinctive flavor.

  • Excess carbon dioxide is dissolved in water under high pressure and low temperature.

  • Due to this technique.

  • The water molecules enclose and trap extra carbon dioxide molecules to prevent them from escaping.

  • Once the excess carbon dioxide is trapped by the water molecules.

  • The bottles are sealed with an airtight cap.

  • This helps maintain pressure inside the bottle and hence, the taste.

  • Do you know why the cold drink tasted flat after keeping it open for some while?

  • This is because when the bottle was opened, the pressure in the bottle was released.

  • The excess carbon dioxide started escaping from the water molecules.

  • After some time, most of the carbon dioxide gas escaped.

  • As a result, the cold drink tasted flat.

  • Hey. That was funny.

  • In reality, when the bottle is sealed, the undisturbed liquid has surface tension.

  • In order to escape, the carbon dioxide molecules require energy to overcome this surface tension.

  • Now, when we shake the cold drink bottle before opening.

  • The trapped carbon dioxide molecules get that required energy.

  • They break free from the liquid's surface tension.

  • As a result, the fizz rises quickly and explodes out.

  • Topic: Thermal Expansion.

  • Why are small gaps left in between rails?

  • Hey. Did you notice that the level of mercury in the thermometer rose when it was placed in hot water?

  • You must be wondering why this happened, right?

  • It happened because of thermal expansion.

  • Thermal expansion is the tendency of matter to expand on heating.

  • This tendency of expansion can be observed in solids, liquids as well as gases.

  • Now let us see how this concept of thermal expansion applies to a thermometer.

  • A thermometer usually consists of a narrow tube with a small bulb at its one end.

  • The bulb and a part of the narrow tube is filled with mercury which is liquid at room temperature.

  • Now, when a thermometer is placed in hot water.

  • Mercury inside it expands due to thermal expansion and as a result its level rises.

  • You must be thinking how the gasoline came out of the tank even though it was exactly filled till the brim.

  • Am I right?

  • Gasoline also expands on heating.

  • So, what happened is that when the tank was filled till the brim, there was no space left in it.

  • Now, when the bike was kept in the sun.

  • The tank became hot which eventually heated the gasoline filled in it.

  • As a result, the gasoline expanded.

  • But since there was no space left in the tank, expansion forced gasoline to come out of the tank.

  • Do you think that the rails bent because of thermal expansion?

  • If yes, then you are absolutely correct.

  • A railway track is made up of a number of rails joined to each other.

  • These rails are usually made up of steel.

  • Steel expands on heating and contracts on cooling.

  • When the rails are joined to one another without leaving any space for expansion.

  • The rails bend due to thermal expansion and the train goes off the railway track.

  • To avoid this, the rails are not joined together firmly.

  • Instead, each rail is connected to the other in such a way that a small gap is left in between them.

  • These small gaps provide space for easy expansion of the rails.

  • Which happens during summer as well as due to continuous friction between the train wheels and the rails.

  • Hence, these small gaps prevent the rails from bending, preventing any kind of accidents.

  • Topic: Mitosis.

  • How does a house lizard regenerate its tail?

  • Have you ever wondered how we grow from a 20 inch new born baby to a 70 inch teenager?

  • This is because every minute millions of cells in our body divide to form new cells.

  • These new cells then further divide to form more cells.

  • In this way, the number of cells in our body increases and we grow taller.

  • Mitosis is a process through which cells in our body divide.

  • Mitosis is used by organisms not only for growth but also for repair, replacement and asexual reproduction.

  • Hey. Were they exact copies of each other?

  • Yes.

  • In mitosis, a parent cell divides to form two identical daughter cells.

  • Both of them have exactly the same genetic material.

  • Hence, they are exact copies of each other.

  • Hey. Did the head of the scarecrow just grow back?

  • Yes.

  • You will be surprised to know that some organisms like a house lizard.

  • Can regenerate their cut or damaged body parts through mitosis.

  • When the house lizard's tail gets cut, it regenerates its tail through mitosis.

  • Each cell around the cut tail starts to divide and forms two identical daughter cells.

  • Again each of these daughter cells further divides to form two more daughter cells.

  • Thus helping the lizard to regenerate its tail.

  • Topic: Atmospheric Pressure.

  • Why don't we get crushed by atmospheric pressure?

  • Hey. Did you hear that?

  • His ears popped.

  • Is this related to atmospheric pressure?

  • Yes.

  • We know that our earth is surrounded by a layer of air called the atmosphere.

  • The gravitational force of earth constantly pulls this atmosphere towards itself.

  • Due to this.

  • The atmosphere exerts a pressure on the surface of the earth as well as on the objects present on its surface.

  • This pressure exerted by the atmosphere is called the atmospheric pressure.

  • This atmospheric pressure outside our body is balanced by the air pressure present inside our body.

  • When the atmospheric pressure decreases, it becomes less than the air pressure inside us.

  • Now, to balance the pressure inside and outside our ears, the air present inside rushes out.

  • Whereas, when the atmospheric pressure increases, it becomes more than the air pressure inside us.

  • So, to balance the pressure inside and outside our ears, the outside air rushes in.

  • This movement of air results in that sudden pop.

  • Have you noticed this before?

  • Has your water bottle ever got crushed once your airplane landed?

  • This happens because of changes in the atmospheric pressure.

  • Generally, the atmospheric pressure in the bottle is equal to that on the surface of the earth.

  • Whereas, in an airplane the atmospheric pressure is low as compared to that on the surface of the earth.

  • During the flight, when you open the bottle and drink some water in the airplane.

  • The atmospheric pressure in the bottle becomes low.

  • This is because the low pressure air present in the airplane occupies the place of water which you just drank.

  • However, when the airplane lands and you come out of the plane, the pressure outside the bottle.

  • The atmospheric pressure on the surface of the earth is high as compared to the pressure inside the bottle.

  • Hence, the outside air exerts a greater pressure on the surface of the bottle than the inside air.

  • As a result, the bottle gets crushed.

  • Wow. How is he able to lift such a heavy car?

  • Are we also powerful enough to handle such a huge amount of pressure?

  • Yes, to some extent we are also carrying a huge amount of pressure.

  • At sea level, the atmospheric pressure is about 14.7 psi.

  • This means that the atmosphere is exerting 14.7 pounds of force on every square inch of our body which is really huge.

  • So, why don't we feel this immense pressure?

  • This is because various parts of our body such as ears, nose, lungs and stomach also contain air.

  • Which exerts pressure on the atmosphere which is equal to the atmospheric pressure.

  • In this way.