This video introduces the concepts of supersaturation, nucleation and crystallisation. The amount of solute that can dissolve in a liquid, i.e. its solubility, increases with temperature. Up to a point, warming a solution makes it possible to dissolve more salt. Using this idea, heat up a beaker of copper sulphate solution, gradually add copper sulphate and dissolve it. This is called supersaturation, since the solution now holds more salt dissolved in it than is possible at room temperature. As the liquid cools, the additional salt will recrystallize and come out of the solution. By providing a rough surface such as a length of string, a process called nucleation occurs, in which a small amount of salt first settles, then grows into a crystal as more molecules deposit on the site. By the time the solution has cooled to room temperature, all the extra salt dissolved is deposited in crystal form along the length of string. *** Warning: Be careful in handling copper sulphate as it is irritating to the eyes and skin, and also can be harmful if swallowed. ***
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In centrifugation, we use the force exerted by rotational motion in order to separate out components of a mixture that have different weights. This is very useful in separating components of a solution that are too light to be separated by sedimentation. We take some muddy water whose heavier particles have already been removed via sedimentation and a solution of calcium hydroxide. Fill two test tubes with muddy water and two test tubes with calcium hydroxide and place all four test tubes in the centrifuge machine as shown. After the machine is rotated for some time, we remove the test tubes and see that we get a precipitate of soil in the muddy water test tubes and a white precipitate in the calcium hydroxide test tubes with clear water on top in all the test tubes. The centrifugal force depends on the mass of the particles and the speed of rotation. With fast rotation even light particles get forced down to the bottom of the test tube as precipitate.
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In this activity we take two capillary tubes of different diameters and place them in a beaker of coloured water as shown. We see that the water rises in both the tubes and that the narrower tube has a higher level of water. As water adheres to glass, the water molecules near the glass walls climb up the glass surface due to adhesion. In this process they also carry up the water molecules that are away from the walls due to surface tension and a small amount of water rises in the capillary tube, forming a concave meniscus. The height to which the water rises depends on the diameter of the tube. In plants, the water is absorbed by the roots and rises up the trunk due to capillary action.
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Here we learn how to prove that the leaves of plants contain starch, which is created as a result of photosynthesis? Remove a plant leaf and heat it in an alcohol bath as shown in the video. The alcohol removes the chlorophyll that makes the leaves green and the heat softens the leaf's cell walls making chemical reactions easier to do . Dip this leaf into a dilute solution of iodine and watch the leaf turn dark green as a result of starch and iodine combining to form a violet coloured complex. Thus, we see that leaves contain starch.
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This activity studies the reaction between metals and acids by dropping some zinc granules into dilute hydrochloric acid and dilute sulphuric acid. In each case, a gas is released and when this gas is tested with a matchstick flame, we get a characteristic popping sound and see that the matchstick burns more brightly. This indicates that the gas produced is hydrogen. Zinc forms the salt zinc sulphate with sulphuric acid and zinc chloride with hydrochloric acid and releases hydrogen gas in both cases. In general, a metal reacts with an acid to form a salt and releases hydrogen gas.
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Starch is a component in many foods. When iodine is added to starch it turns blue. That is why, in the experiment, the solutions in both beakers turn blue. On addition of saliva which contains an amylase, a starch digesting enzyme (chemical compound that catalyses the breakdown of starch); the starch gradually converts to sugar. Once the starch is broken down, the blue colour disappears. It is important to know that the salivary amylase requires an alkaline medium to act.
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This video introduces the idea that rolling is more efficient than sliding, when it comes to doing useful work. This is the basis of the ball-bearing, which is an essential part of a lot of mechanical things - cars, skates, roller blades, shopping carts...the list is long indeed. When marbles are used to hold two petri dishes apart as shown in the video, the dishes are far easier to rotate than without the marbles. This is because the spherical shape of the marbles makes it possible for them to roll between the two surfaces, so the surfaces do not have to slide against each other. This greatly reduces the friction between the surfaces and correspondingly the effort needs to produce movement is reduced as well.
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The beautiful shapes and colours of some crystals are formed due to the water of crystallization. These crystals require water to maintain their crystalline properties. So let's see what happens when you remove the water of crystallization from crystals by heating it. Take some copper sulphate in a test tube and heat it. you see that it loses water and turns into a white powdery substance termed anhydrous copper sulphate. When we add water to this powder it immediately regains it blue colour and crystalline shape. As a result of this property, chemicals like copper sulphate are known as hydrous substances or hydrates. *** Warning: Be careful in handling copper sulphate as it is irritating to the eyes and skin, and also can be harmful if swallowed. ***
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In this activity we explore the nature of metallic oxides. By burning a strip of magnesium, we obtain magnesium oxide which we then dissolve in water. We test this magnesium oxide solution with litmus paper. The solution does not affect blue litmus but turns red litmus blue. This tells us that magnesium oxide is basic or alkaline in nature. In general, metal oxides are basic in nature.
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A polar molecule is one in which the atoms are arranged such that one end of the molecule has a positive charge and the opposite end has a negative charge.In this video we see that polar substances only dissolve in polar solvents and non polar substances in non polar solvents. Potassium permanganate, a polar compound, is added to water, a polar solvent and to carbon tetrachloride, a non polar solvent. We see that it dissolves only in water. In a similar fashion, a non polar element iodine is added to the same two solvents. This time, we see, that iodine only dissolves in carbon tetrachloride.
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This video shows the difference between saturated and unsaturated fats. Saturated fats have only single bonds in their molecular structure. This means they are saturated with hydrogen atoms. These fats are solid at room temperature. Saturated fats are considered a risk factor in heart disease. Unsaturated fats, on the other hand, are considered the healthier option. They are liquid at have room temperature.
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Measuring cylinders help in finding volume of liquids, but what of bodies with irregular shapes? This video shows how to use the water displacement method to measure the volume of bodies. A measuring cylinder or overflow vessel is used to determine two volumes - the volume before a body is immersed and the volume with the body immersed. The reasoning is that the immersed body has displaced its own volume, so by calculating the difference in volume of water, we can find the volume of the body. Once we find the mass of the body, the density can then be calculated as mass/volume. Note that this method only works of the object whose volume is to be measured completely sinks in water.
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In this experimental set up 3 potatoes - 2 raw and 1 cooked are used. All 3 have a cavity and are placed in a tray of water. One of the raw potatoes and the cooked one have salt filled in their cavities. The cavity in the other raw potato is left empty. When the potatoes are observed some time later, the salt in the raw potato is dissolved in water, while the salt in the cooked potato is still in the solid form with no water. The 3rd potato is without water. What happened here is like this. Because of osmosis, the cells of the potato surrounding the salt filled cavity gave out water into the cavity. This water is drawn from the water lying in the tray. The cooked potato cells are dead and so do not undergo osmosis. So no water is drawn in and the salt remains dry. In the case of the 3rd potato, as there is no salt, the cells do not develop sufficient osmotic pressure to draw in water..
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This video introduces the concept of atmospheric pressure and demonstrates how it causes your refreshing beverage to rise up through a straw into your mouth. Atmospheric pressure acts equally in all directions and on all surfaces at once. The video explains how holding one end of a straw closed in a liquid causes the liquid to get magically "lifted" along the straw. Actually the rise happens due to the pressure difference as the air in the straw is at a lower pressure than the air outside the straw. In the same way, sucking on one end of the straw evacuates some air and reduces the pressure, allowing the air outside to push the drink into the straw.
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The activity in this video demonstrates how a low pressure environment inside an enclosed space is dangerous. We first partially fill a bottle with boiling water. This drives air out of the bottle, replacing it with water and steam. Then we seal the bottle to prevent air from getting back into the bottle. As the bottle is cooled steam condenses to water and the pressure in the bottle drops significantly below the atmospheric pressure of the air outside. This difference in pressure crushes the walls of the bottle. This is the reason submarines have a maximum depth rating, if they go lower than their rating then the pressure exerted by the water will crush the submarine.
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This activity shows that the colours that are seen by human beings are largely dependent on the colour of light used. The colours seen under white light or sunlight appear different when seen through red, blue and green coloured screens or filters. Under white light, an object absorbs all colours expect one which it reflects and this is the true colour of the object. But on using a filter, light of only one colour falls on an object and depending on how it reflects and absorbs this light, the object changes colour or may even become invisible!
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If we leave a glass of water in the open air for a few days, the water will turn it slightly acidic. This happens because the gaseous carbon dioxide in air dissolves in water to form carbonic acid. Like carbon dioxide, which is an oxide of a non-metallic element (Carbon), this property is also true generally true for oxides of other non-metals. The video demonstrates the heating of sulphur in a test tube until it oxidizes (burns) and releases sulphur dioxide smoke. Sulphur dioxide does not affect red litmus but changes the colour of wet blue litmus paper to red, showing us that sulphur dioxide gas is acidic. Sulphuric acid is produced by dissolving sulphur dioxide in water. Many industrial processes produce sulphur dioxide gas as a pollutant and when this gas dissolves in rain water, we get acid rain which is harmful to the biosphere.
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This activity shows how a pencil in a half filled glass of water appears to be crooked or bent at the boundary of the water and air. This is known as refraction of light. Light travels at different speeds in different mediums and it travels more slowly in denser mediums. The famously known value for the constant speed of light, is actually its speed in the vacuum of space. When lights enters the atmosphere from space, it slows down slightly to adjust to the density of air. When it enters water or glass from air, it slows down even further as these mediums are denser than air. A consequence of having different speeds in different mediums is that a ray of light bends when going from one medium to another. This bending of light as it goes from water to air before reaching our eyes is what makes the pencil appear bent.
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This video discusses one of the easiest and well known methods of purifying water. First we let muddy water remain undisturbed for a few hours. The large particles settle down due to gravity but the water still has many small particles suspended in it. Carefully, without disturbing the bottom layer, pour some of this muddy water in to another beaker, This process is called decantation. This water is not yet fit for consumption, though since it has finer particles that are visibly suspended in it, but are too small to separate through sedimentation.
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This activity shows the difference in the behaviour of lenses and prisms. Convex lenses converge light rays (bring them together) while concave lenses diverge rays of light. As a result, either a smaller or a larger image can be formed by a lens. A prism on the other hand does neither, it only diverts the beam of light, purely by refraction.
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Soaps are formed when fatty acids react with an alkali. The reaction is called saponification. The video shows how to make soap. An alkali, sodium hydroxide, is taken in a test tube. Some vanaspati is added to the test tube and the mixture is heated. When the mixture is shaken, froth collects at the top indicating the formation of soap.
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Metals like copper and magnesium react with oxygen present in the air and form their respective oxides. copper oxide and magnesium oxide. Such metallic oxides react with acids to form salts such as chlorides and sulphates, which are usually soluble in water. In this video we take copper oxide and hydrochloric acid to it. The reactions forms copper chloride, a soluble salt.
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Dissolution of substances in water sometimes involves exchange of heat. In this video 3 compounds sodium hydroxide, ammonium nitrate and sodium chloride are dissolved in water. The temperatures of the solutions are noted after each dissolution. The sodium hydroxide dissolves with release of heat making it an exothermic dissolution. The ammonium nitrate dissolves by absorbing heat; an endothermic dissolution. Only the sodium chloride dissolves with a marginal change of temperature.
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This activity uses a base, sodium hydroxide and an acid, dilute hydrochloric acid, to be made part of an electrical circuit. By turns, it is seen that the bulb glows even when the wire is detached, and the acid or base is used for completing the circuit. Both acids and bases have charged particles called ions in them, and this gives them electrical conductivity.
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Watch how a water based solution of turmeric, a common South Asian cooking spice, can be used as an acid-base indicator. Turmeric only changes colour in the presence of a base, and not in the presence of an acid. An indicator is a substance that changes its colour depending on the pH value of a liquid. Bases such as a soap solution have a pH value greater than 7, whereas acidic liquids like lemon juice have a pH value less than 7. The normally yellow turmeric changes to red-orange when dropped into soap solution, indicating that the soap solution is basic. When acidic lemon juice is slowly added to this, the red-orange gradually weakens and the original yellow is seen again, showing that the acidic lemon juice reacted with the basic soap solution, and turned the liquid to neutral
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This activity aims to convey an idea of the scale at which matter exists, of how tiny atoms and molecules are. Even after diluting a coloured liquid like a potassium permanganate solution over and over again we that there is still a hint of colour even in the most dilute solution. This tells us that there must be a large number of very small particles in the small amount of potassium permanganate that we dissolved to make the first solution.
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This is a demonstration of the Archimedes Principle which states that when an object is immersed in a fluid it apparently loses weight and the apparent loss is equal to the weight of the fluid displaced by the object . Use a spring balance to weigh a potato in air, then immerse it completely in water using the beaker and overflow apparatus shown in the video. Collect the displaced water and measure it. The weight lost by the potato bobbing in water is equal to the weight of the displaced, or overflow liquid. This is the essence of Archimedes' Principle, which connects the upthrust of water (buoyant force) to the apparent weight loss of a body immersed in water, to the weight of the liquid that is displaced - all three are equal.
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This activity shows which foods contain starch. The indicator used is iodine. Iodine, a yellowish brown liquid, when added to rice and potato turns blue black. This is because when iodine reacts with starch, it forms a complex made up of polyiodide chains. Such a reaction is not seen when iodine is added to sugar and salt.
Views: 71259 KClassScienceChannel
The electronic devices we are surrounded by, all run on batteries. One of the earliest batteries is a voltaic cell that is created by placing two different kids of metallic electrodes in a diluted acid solution. Such cells are called wet cells or wet batteries, and are used today mainly in cars and uninterrupted power supplies (UPS). Here we make such a cell by using a zinc plate, a copper plate and use hydrochloric acid as the electrolyte. The zinc plate loses electrons to the copper plate, setting up a current in the circuit and making the bulb glow. By and large, the modern batteries are dry cells where the electrolyte is a paste.
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When an object is immersed in a liquid and its weight is measured, we find that the weight is lower than the weight of the object in air. The reason for this is the buoyant force exerted by the liquid on the object. The buoyant force acts against gravity and gives the object an upward push, thus reducing the weight of the object. This video demonstrates that the buoyant force is different for different liquids and it depends on the density of the liquid. The denser the liquid, the greater the buoyant force.
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When an aluminium foil is placed in a tub of water, we see that it sinks. This is expected as aluminium is denser than water. When some foil is crumpled and put it in water, we see that it floats even if we try to sink it. On the other hand, if we crumple the first foil that is already sunk, it stays sunk. When we crumple the foil outside, some air gets trapped in the folds of the foil and this trapped air provides the buoyant force that does not allow the crumpled foil to sink. In the latter case, as the foil is crumpled under water, there is no air that can get trapped in the folds of the foil and the foil remains sunken.
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This video explains why soap is used to remove oil and grease. We know that oil and water do not mix. So, water alone cannot remove oil stains. In this video we see that even after the 2 liquids are mixed together vigorously in a test tube they separate, with the oil lying above the water. However, when in addition to water and oil, some liquid soap is added and the mixture is vigorously shaken, the separation of oil and water is not seen. This is because soap has both hydrophilic and hydrophobic ends. The hydrophilic end combines with water and the hydrophobic end with the oil allowing the formation of an emulsion. This property of soap allows oil to combine with it and so soapy water can remove oil stains.
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String up a pendulum, move the bob to one side and let go to set the pendulum into oscillations. Use a stopwatch to measure the time the pendulum takes to complete ten oscillations. Diving this time by 10 gives us the period of the pendulum i.e. the time taken to undergo one oscillation. Decrease the pendulum's length and repeat the above to get the new time period. We see that as the length becomes shorter, the time period decreases. This shows us that the length of a pendulum and its time period are related
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The melting point of napthalene can be determined by stuffing some into a capillary tube, strapping a thermometer to it, and immersing it a hot bath. As the temperature of water rises, at a particular temperature the napthalene melts out of the capillary tube. Note the temperature, that is the melting point.
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If the air is blocked off, would it be possible to drink from a straw? This activity answers that question - insert a straw into a bottle with some juice and suck from it to make sure that it is possible to drink the liquid. Then, use putty to seal off the gaps around where the straw enters the bottle, so that the inside of the bottle is totally cut off from the atmosphere outside. After doing this, it is impossible to drink water by sucking on the straw. It is atmospheric pressure that makes it possible to drink water from a straw - sucking on the straw reduces the pressure inside it but more importantly, it sets up a pressure difference between the inside of the straw and the atmopherere outside. The atmosphere attempts to equalise the pressure by pushing down on the liquid, sending it rising up through the straw.
Views: 20632 KClassScienceChannel
In this activity, we measure the percolation rate of different kinds of soils like sandy soil, loamy soil and clay. Percolation rate is the speed at which water flows though a column of soil. Take three identical conical flasks with funnels and plug the funnels with some cotton as shown. Add 20 grams of sandy soil, loamy soil and clay in the three funnels, then slowly add 50 g of coloured water over the soil and leave the flasks undisturbed for some time. After a while, pour the water collected in the flasks into three beakers. You will see that the flask under the sandy soil has the most water and the flask under the clay has the least water. The sandy soil has the largest particle size while the clay has the smallest particle size. This tells us that the percolation rate depends directly on particle size and is the highest for sandy soil while the clay soil has the highest retention capacity.
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Refraction causes light to bend as it passes from one material to another and the amount of bending depending on the refractive index of the material. In this activity we place a small beaker inside a larger beaker. We then fill the small beaker with vegetable oil, allowing the oil to overflow till the large beaker is filled as well. We find that the small beaker disappears when we do this! The glass of the beaker and the vegetable oil have refractive indices that are almost equal. Thus , as light passes from the small beaker to the oil outside, the light does not bend too much and we cannot see the small beaker.
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This demonstration shows how heat affects the rate of reaction. Potassium permanganate reacts with oxalic acid in a classic reduction-oxidation reaction, in short called an redox reaction and the end products are carbon dioxide gas which bubbles away and colourless manganese ions and water are left behind. We carry out the reaction in two test tubes, one of which is placed in hot water while the other one is placed in cold water. We see that the solution in hot water decolourizes first. Thus, we see that heat speeds up the rate of a reaction. While our conclusion is generally true there are exceptions to it. If we heat a chemical substance so much that it loses its structure then we may not even get a reaction, An example of this is enzyme catalyzed reactions which happen in a specific temperature range. Too much heat destroys the enzyme structure and kills the reaction.
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In this activity, we use a digital scale to find the mass and a graduated cylinder to find the volume of two cubes which are made of iron and aluminium respectively. From these measured values, we then calculate the densities of the two elements and find that iron is denser than aluminium.
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A mixture of two liquids can be separated out into the two distinct liquids by using chemical properties. In the case of a mixture of water and alcohol, being aware that their boiling points different will help. Alcohol boils at 87 Celsius which is lower than the boiling point of water, 100 Celsius. When bringing the mixture to boil, alcohol will escape first and can be trapped and distilled. While alchohol is still boiling, temperature remains fixed at 87 and does not rise. The temperature starts rising only when all the alcohol has evaporated. Separating a mixture by exploiting a difference in boiling point, is called distillation
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Starch iodide paper is an indicator for strong oxidising agents like chlorine gas and nitrites. In this video we learn how to make this indicator. Starch is mixed in water and heated. A small amount of potassium iodide powder is added to the starch solution and the mixture is boiled. A strip of filter paper is then dipped into the solution such that it is well coated and hung out to dry. The starch iodide paper is now ready. It is then tested by placing it in an environment of chlorine, obtained by mixing bleach and vinegar. The paper turns blue black.
Views: 12232 KClassScienceChannel
In this activity we explore how conduction works. We affix pins on a metal spoon with the help of some molten wax. As we heat the spoon, we observe that the pins fall of one after another, staring from the pin that was closest to the spirit lamp. This method of heat transfer is called conduction and takes place only in solids. In conduction the particles in the object transfer heat without moving from one place to another in the object.
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This activity uses a bar magnet, iron filings, and a clean white surface on which to watch the action of the magnet on the iron filings. The fact that a magnet attracts certain metallic objects is well known, but the magnetic field is invisible. This video shows how to use iron filings to reveal the shape and size of the magnetic lines of fiorce. The space around the magnet where its influence can be demonstrated, is callled the magnetic field. The demonstration shows some distinct characteristics - the lines of force attempt to form closed loop from pole to pole, they never intersect, and they're all the same strength. The concept of magnetic field strength is informally introduced as the number of lines per unit area. The video closes by asking about the Earth's magnetic field - do you have an idea how the field can be detected or demonstrated?
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Some substances when heated go straight from a solid state to a vapourous state, entirely skipping the liquid phase. This is called sublimation. This activity uses the fact that ammonium chloride sublimates in order to separate it from chalk powder. Heating a mixture of chalk and ammonium chloride leaves behind pure chalk powder, the sublimated ammonium chloride can be collected and condensed at the exit.
Views: 62275 KClassScienceChannel
The potato is an underground stem. The eyes of the potato are nodes from which fresh buds sprout. In this activity a potato is cut up into small pieces and provided with water and air. Soon the pieces of the potato with eyes develop buds and grow. They will grow into new plants. This method of reproduction without gametes is called vegetative propagation
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In this activity, we learn how loudness of sound is related to the amplitude of vibrations. We fill a steel glass with some water and then strike the rim of the glass with a spoon . We do this many times, increasing the hardness with which the spoon is hit every time. We observe that each time the sound produced is louder. Then we place a light polystyrene ball close to the glass as shown in the video and repeat the earlier step. We see that each time the ball jumps a little farther from the glass. This tells us that as the amplitude of vibrations gets larger, the sound produced becomes louder.
Views: 32060 KClassScienceChannel
The video discusses a phenomenon that most people have commonly seen. Mist forms on any cold, smooth surface like the outside of a glass of ice water or the outside of a car's windshield in cold weather. If there is enough mist, it coalesces into drops and runs down the surface, Dew drops are formed on leaves by the same method but they only form overnight when the lowest temperature of the day is achieved. When the temperature is low enough, the water vapour in air condenses on cool surfaces like blades of grass and leaves to form dew drops.
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Using a small light source such as an incandescent bulb, shadows are seen to be sharply defined. The outline of the shadow is sharp and there is stark contrast between the lit and unlit areas. Using a diffused light source such as a CFL lamp changes the nature of the shadow and there is area of half-light, half-shadow. The region of complete shadow is called the umbra and the region of diffuse shadow is called the penumbra. These shadows are formed on the Earth during a solar eclipse and From the umbra we see a total eclipse while from the penumbra only a partial eclipse is visible.
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Observe a scale or a measuring tape. The inches show sub-divisions, and the sub-division is the smallest distance that can be measured. This is technically kNown as the "least count" of the scale.
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The principle behind suction cups is explained in this video. Suction is a phenomenon that happens because of atmospheric pressure. If a little air is removed or evacuated from a small enclosed space, that space experiences lower pressure. Because of the lower pressure in a small area, the atmospheric pressure outside pushes down on it and holds it firmly in place. Suction cups will hold on until either the cup is lifted from the side allowing air in and makes pressures equal or by applying a force large enough to overcome atmospheric pressure.
Views: 42535 KClassScienceChannel