Subtitles section Play video Print subtitles Smart Learning for All. Topic: Electric Charge. How does a plastic comb attract paper? What? You don't believe me? Ok. Let us try. Take a plastic comb and bring it close to some pieces of paper. Hey, Wait. Don't laugh. We need to do something first. Rub the comb on your dry hair and then bring the comb close to the pieces of paper. See, I was correct. The pieces of paper got attracted to the plastic comb. Do you think it is magic? No, the reason behind this is electric charge. Electric charge is the quantity of electricity held in an object. There are 2 types of electric charges, positive and negative. However, there are some objects where the positive and negative charges are equal to one another. In such cases, we say that the object is electrically neutral. So, was the plastic comb initially electrically neutral or electrically charged? Initially, the plastic comb was electrically neutral. That means it had equal number of positive and negative charges. Hence, it did not have the ability to exert a force and attract the pieces of paper. So, after rubbing the plastic comb on our dry hair, why was it able to attract the pieces of paper? I will tell you why. When we rubbed the plastic comb on our dry hair, it gained an electric charge. Once it got electrically charged, it got the ability to exert a force on the pieces of paper and attract them. This charge is called as static electricity. However, do you think, like a plastic comb, a metallic comb will also attract the pieces of paper? No, you are wrong. A metallic comb will not attract the pieces of paper like the plastic comb. Wondering why is that so? It is because plastic is not a good conductor of electricity. It does not allow the electric charges to flow through it onto the earth. As a result, the charges build in the plastic comb. Making it electrically charged and enabling it to attract the pieces of paper. However, metal is a good conductor of electricity. It does not let the charges build in it. It allows the electric charges to flow through it onto the earth. Thus, not allowing the metallic comb to get electrically charged. As a result, the metallic comb does not attract the pieces of paper. Topic: Neutralization Reaction. How to treat a bee sting? Hey. Hold On. Don't go near that honeycomb. Please listen to me. It is quite dangerous. Fine. Go ahead. See, I told you. Ok. Now, don't worry. Put this baking soda solution on the bee stung area. You got some relief, right? Do you know why you got relief? This happened because a neutralization reaction took place when we applied baking soda on the stung area. The venom of a honey bee contains formic acid. When it stings us, it injects that acid into our skin. Formic acid causes immense pain and irritation. However, when we apply baking soda solution, which is a mild base, on the stung area. It neutralizes the formic acid and cancels its effect. As a result, the sensation of pain and irritation decreases and we get some relief. Such a reaction between an acid and a base is called neutralization. In neutralization, both acidic and basic solutions neutralize the effect of each other. The nature of both acids and bases gets destroyed. Hey, Wait. What are you doing? Don't tease that insect. It is not a honey bee. It looks similar to a honey bee but it is a bit longer. It is called a wasp. At least this time listen to me. Ok. Don't listen and bear the consequences. Applying the baking soda is not going to help. See, nothing is happening. I will tell you what to do. Pour this vinegar on the stung area, you will get some relief. Why do you think the baking soda solution did not help in this case? Earlier, in case of the honey bee, we learnt that its venom is acidic. Hence, baking soda, being a basic solution helped to neutralize the effect Now, in case of a wasp, the nature of its venom is basic. When it stings us, it injects that venom into our skin. This venom causes us pain and itching. Now, baking soda is also a basic solution. Hence, it will not provide any sort of relief. However, when we pour vinegar, which is a mild acid, on the stung area. The acid, that is, vinegar and the base, that is, the wasp's venom get neutralized. As a result, the sensation of pain and itching decreases and we feel better. Topic: Nuclear fusion. Why is nuclear fusion not used to generate electricity? You really want to know the answer to this, right? But wait. Before answering the question, let us understand what is meant by nuclear fusion. When two lighter nuclei combine to form a heavy nucleus, a large amount of energy is released. This process is called nuclear fusion. Where does this nuclear fusion take place? You think that it takes place in a laboratory? No, you are absolutely wrong. Nuclear fusion takes place in the sun. The nuclei of two hydrogen atoms join together to form a heavy nucleus of helium with the release of a large amount of energy. How do you think this energy reaches us? No. It does not reach us through power lines. Wait I will tell you. The energy released after nuclear fusion reaches us in the form of sunlight, ultraviolet radiations, heat, etc. Hey. But we are already producing electricity with the help of nuclear fission. So, why do we require nuclear fusion? For this, you need to first understand the difference between nuclear fusion and nuclear fission. As we already know, nuclear fusion is the fusion of two lighter nuclei. With the release of a large amount of energy. The exact opposite process happens in nuclear fission. Here, a heavier nucleus splits into two lighter nuclei, releasing a large amount of energy. This process of fission is used in nuclear power plants. Where a heavy nucleus of uranium is split into lighter nuclei. The energy that is released in this is used to generate electricity. However, there is a major disadvantage of nuclear fission. Wondering what it is? The major disadvantage is that uranium is a radioactive element. When uranium undergoes fission, it generates radioactive waste along with energy. This radioactive waste is very harmful for most lifeforms and the environment. Hence, we need to find a clean and safe source of energy to generate electricity. What source would that be? Would it be nuclear fusion? You are right. Then why are we not harnessing the energy of nuclear fusion to produce electricity? This is because, for nuclear fusion, two conditions are required. They are high pressure and high temperature. Only when these conditions are met, can the two nuclei travel at very high speeds resulting in collision. On earth, it is extremely difficult to create such high pressure and temperature. Even if we are somehow able to create these conditions, the question is how will we control them? As there are many questions unanswered and unsolved. We have not yet succeeded in using nuclear fusion in the production of electricity. Topic: Sound. Why do we hear echoes? Hey. Hold On. Don't go into that room. You don't want to listen to me. Ok. Then go ahead. See, I warned you. Will you listen to me now? Don't worry. The sound you heard was just an echo of your voice. Let me explain what an echo is. When we speak or laugh in a big empty hall, we hear our own sound repeatedly. This is because our sound waves get reflected from the walls of the hall back to us. The reflected sound that we hear is called an echo. Hence, an echo is defined as the repetition of sound. Caused by the reflection of sound waves from a hard surface back to the listener. Hey. What are you doing? Are you trying to hear an echo? It is not that easy. There are 2 ideal conditions for an echo to be heard. When we speak or laugh, we hear our original sound at that moment. The sensation of this original sound remains in our brain till 0.1 seconds. This time is called the persistence of hearing. When we utter sounds, some of our sound waves get reflected while some get absorbed. If the reflected sound waves reach our ears before the completion of 0.1 seconds. Then our brain does not perceive the original and reflected sounds as separate sounds. They are interpreted as one sound, therefore, in order to hear two distinct sounds or an echo. The time gap between the original sound and the reflected sound or echo should be at least 0.1 seconds. This is the first condition for an echo to be heard. Do you know when the time gap will be more than 0.1 seconds? This gets us to the second condition for an echo. The minimum distance between the speaker and the reflecting surface should be at least 17.2 meters. When the distance is 17.2 meters and we start speaking. Assume that the original sound reaches our ears at this time and the reflected sound reaches our ears at this time. Then the time interval between the reflected sound and the original sound will be equal to 0.1 seconds. As a result, we will be able to hear an echo. Alright. Now, let us try and hear an echo in this room? It is even bigger than the previous room. Now, why can't we hear an echo? This is because there are many soft furnishings like sofas, carpets, curtains, etc., in this room. They absorb most of the sound waves. As the sound waves do not get reflected, we are not able to hear an echo in this room. Hence, one more thing to consider, if we want to hear an echo. Is that there should be minimal use of such sound absorbing materials. Topic: Ear. How do ears help with balancing? They really do. You don't believe me. Ok. Can you play a guitar and walk at the same time? How do you think you are able to maintain your balance? Do you know why you can't balance yourself anymore? Wait, I will tell you. This happens because there is a connection between our ears and body balance. Our ear consists of 3 parts, outer ear, middle ear and inner ear. Our inner ear works in sync with our eyes and muscles. Helping us maintain balance, while we are doing various activities. The inner ear consists of three semicircular canals. Called superior semicircular canal, posterior semicircular canal and lateral semicircular canal. The three semicircular canals are arranged in three different positions. Each of these canals has a fluid called endolymph and hair cells called cilia at the base. Whenever we move our head, the fluid moves, resulting in the movement of the cilia as well. When the cilia moves. It sends signals to the brain informing which direction our head has just moved in. Each canal has different functions as per the movement of our head. When we move our head up and down. The superior semicircular canal helps our brain to understand the yes motion. When we tilt our head towards our shoulders. The posterior semicircular canal helps our brain to understand the tilting motion. When we move our head from side to side. The lateral semicircular canal helps our brain to understand the no motion. It was too complicated, right? Ok, don't worry about it. Relax. Why don't you go on a merry go round ride? Hey. Why were you not able to maintain your balance? This is because when you sat in the merry go round and started rotating. The fluid in the semicircular canals also started to move. After a while, it was moving at the same rate at which you were moving. However, when the ride stopped and you got down from the ride, the fluid was still in motion due to inertia. Hence, even though you were not moving. The moving fluid gave your brain false information telling you that you are still in motion. Thus, you were not able to maintain your balance. Topic: Rancidity. Why is a bag of chips half full? Looks like you don't believe me. Open the bag. See I told you. The bag of chips is indeed half full. Why is that so? It is mainly because of a concept called rancidity. When food becomes rancid, it develops an unpleasant smell and taste and it becomes unsafe for consumption. Rancidity generally refers to a condition. Where the fats and oils present in food get oxidized, resulting in food spoilage. Since the chips contain fats and oils, they are likely to get rancid. Therefore, to prevent this, nitrogen gas is flushed into bags of chips by manufacturers. But, why nitrogen? Nitrogen does not react with fats and oils. As a result, rancidity does not take place. Moreover, a gas in the bag serves as a cushioning agent and prevents the chips from crumbling. That is why the bag of chips is only filled till half. Topic: Concave Mirror.