অষ্টম শ্রেণীর পরিবেশ ও বিজ্ঞান অধ্যায় 1.3 - তাপ পাঠ্য বইয়ের বিস্তারিত আলোচনা পর্ব - ২
অষ্টম শ্রেণীর পরিবেশ ও বিজ্ঞান অধ্যায় 1.3 - তাপ পাঠ্য বইয়ের বিস্তারিত আলোচনা পর্ব - ২
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00:00We started with the topic of heat, and this is the second video on the topic of heat.
00:20In the previous video, we discussed the units of heat, and there we saw that if something
00:28becomes hot, the amount of heat that is required depends on the subject.
00:37This time, the topic of this video is the change of situation and the use of lean heat.
00:45It is a very important topic, so we will try to understand it as well as we can.
00:52So, what is the change of situation?
00:54If we do not use heat on any object, or if we do not apply heat on it,
00:59then the heat that is used on the object, or the heat that is released on the object,
01:05as a result, the object changes from one state to another state, or to another state.
01:13The process of this change is what we call the change of situation.
01:20Now, the question is, the change of situation,
01:23there is a very small and beautiful example in your mind,
01:26that if you take a cup of water and heat it for some time,
01:33in a beaker, the temperature will increase naturally.
01:37Or, if you take a cup of ice at 0 degree Celsius,
01:42and heat it, as you can see in the picture,
01:45what happens as a result of heating?
01:47As a result of heating, it takes time to melt.
01:52As it melts, the ice changes from a difficult situation to another.
01:56That means, the ice at 0 degree Celsius,
02:01changes to water at 0 degree Celsius.
02:06That means, there is no change in the temperature.
02:10The amount of heat that is applied, is called the temperature of the ice.
02:14And this temperature, where there is no change in the temperature,
02:18is called the melting point.
02:20We will discuss this later.
02:22So, this event, where there is no change in the temperature,
02:26and the ice changes to water at 0 degree Celsius,
02:32is called the melting point.
02:34So, in this way, if you heat a difficult object for a long time,
02:39then it changes to water at 0 degree Celsius.
02:41But, in that case also, there is a constant temperature.
02:45It is not always 0 degree Celsius.
02:47It is 0 degree Celsius in the case of ice.
02:50The temperature of the ice, or we can say,
02:53the temperature of the water, the temperature of the ice,
02:56all are 0 degree Celsius.
02:58That is why it is 0 degree Celsius.
03:00So, in the case of different difficult objects,
03:02the temperature will be different.
03:04So, this constant temperature,
03:06the temperature, which is created from a difficult object to an ice object,
03:12we call it the melting point of the object.
03:16Now, the question is,
03:18this melting point, the melting point,
03:20can come in the form of a constant in the experiment.
03:22So, what do we say?
03:24When there is a constant temperature, a difficult object,
03:26when it is heated, it changes to water at 0 degree Celsius.
03:30In this event, we call it the melting point.
03:32So, there are different events like this.
03:35Before that, we will see one more thing.
03:38The way the ice melts and changes to water,
03:41if we keep the same water in the freezer,
03:44then it will change to ice again.
03:47So, what happens when a difficult object melts and becomes difficult?
03:53The heat is released.
03:55That means, it produces heat.
03:58That means, the heat is released.
04:00We call this event the difficult event.
04:03So, you have to keep this in mind.
04:05That means, when there is a constant temperature,
04:08the ice becomes difficult to melt.
04:10As we have seen in the previous example,
04:13when there is a constant temperature of 0 degree Celsius,
04:15the ice becomes difficult to melt.
04:17So, this is another example.
04:18Now, the heat that is released,
04:20that heat remains.
04:22That means, there is a constant temperature,
04:24in a constant object,
04:26in which the ice becomes difficult to melt.
04:29We call it the melting point.
04:32You can see a graph on the screen
04:34where the names of different objects are given.
04:37There are the values of the objects.
04:38You can see the graphs.
04:40Here are the values.
04:41In which temperature does the ice become difficult to melt?
04:44Here are the values of the ice.
04:46In which temperature does the ice become difficult to melt?
04:49You can remember these or ask questions in the exam.
04:52What is the value of the value of the ice?
04:54What is the value of 1000, 83 degrees Celsius?
04:56What is the value of the ice?
04:57Or what is the value of the ice?
04:59So, the meaning of the word Himank is a direct meaning of the word Himank.
05:06The meaning of the word Himank is a direct meaning of the word Himank.
05:09So, what do we think?
05:10That the meaning of the word Himank is the same as the meaning of the word Himank.
05:14But, it is not the same for everyone.
05:16Generally, it is the same.
05:17As I said earlier, there are some exceptional examples.
05:21For example, in the case of glass, in the case of butter, in the case of churbi, in the case of moong, in the case of peach,
05:26there is no direct meaning of the word Himank.
05:29Again, the meaning of the word Himank is not the same as the meaning of the word Himank.
05:34Now, we will see how to change the meaning of a word in a difficult way.
05:41We should not forget that the meaning of a word will not increase if it is changed from difficult to easy.
05:48Apart from that, when the meaning of a word is changed from difficult to easy,
05:51in that case, the meaning of the word will remain the same.
05:53It will not increase or decrease.
05:55Now, what happens normally?
05:57If there is no direct meaning of a word,
06:00when the situation changes,
06:02then if the meaning of the word decreases,
06:04the meaning of the word increases.
06:06Because, the meaning of the word increases when there is a direct meaning of the word.
06:08That means, the meaning of the word has a direct relationship with the meaning of the word.
06:11That means, it is inversely proportional.
06:13That is why, there is an opposite relationship.
06:15One increases and the other decreases.
06:17That means, when the situation is difficult,
06:19the meaning of the word is usually opposite to the meaning of the word.
06:24So, there is an example.
06:26You can understand it better if you see it.
06:28It is in Chapter 1 and 2.
06:30There are two test tubes.
06:32There are some molds.
06:34And there is a piece of ice in one of them.
06:36So, what are the two test tubes doing?
06:38No, they are being heated.
06:40So, what are the molds and the ice?
06:42They are melting.
06:43Now, in the test tube where the mold is melting,
06:45a small piece of the mold is thrown in it.
06:48And in the test tube where the water is present,
06:50a piece of ice is thrown in it.
06:53Now, what can we see if we look at the picture carefully?
06:56So, in the first picture,
06:58the piece of the difficult mold is
07:00submerged in the liquid mold.
07:03You can see it in the diagram.
07:05It is submerged.
07:06If the piece of the difficult mold
07:08touches the hot liquid mold,
07:10it will melt very quickly.
07:13But if you look at the picture next to it,
07:15when the piece of ice is thrown in it,
07:17it is stuck on the liquid mold.
07:20The reason for this is not clear.
07:22So, we can say that
07:25the density of the difficult mold
07:28is much more than that of the liquid mold.
07:32But the density of the difficult mold
07:35is less than that of the liquid mold.
07:38That is why it is stuck like this
07:40and is submerged.
07:42So, if this is the case,
07:44we can use other examples.
07:48For example, if the water is thrown in the ice,
07:50does it increase or decrease the density?
07:52That is one thing.
07:54Remember, if the water is thrown in the ice,
07:56does it increase or decrease the density?
07:58Now, when the liquid mold is thrown in the difficult mold,
08:01does its density increase or decrease?
08:04We need to know that too.
08:06For example, let me give a small example.
08:08Because the water is thrown in the ice,
08:10there are advantages and disadvantages.
08:12For example, in Sripadandesh,
08:14the water in the radiator of our car
08:17is thrown in the ice.
08:20Since the temperature in Sripadandesh
08:22is below 30 degrees Celsius,
08:25the water is thrown in the ice.
08:30The radiator pipe is thrown in the ice.
08:36In the case of water supply in the house,
08:40the pipes in the house are also thrown in the ice.
08:45In the case of the water in the middle of the wall,
08:49the pipes are thrown in the ice.
08:52The wall is also thrown in the ice.
08:54That is why we can hear the sound of the ice in the mountains.
08:58But what do we know?
09:00The water content of the ice is less in the ice.
09:02That is why we can hear the sound of the ice in the water.
09:05But what is there in the ice?
09:07There is water.
09:09The water content of the ice
09:11and the low water content of the ice
09:14make the fish swim beautifully.
09:17Therefore, we can say that
09:19if the water content of the ice is low,
09:21the house and the density of the house
09:23will decrease.
09:26For example, in the case of Dhalai Lohar,
09:28Pitol Lohar and Shanta Isha Polat.
09:30If there is a statue of the Dhatu
09:33lying on the roof of the house,
09:35people will try to find out
09:37where the Dhatu or statues are lying.
09:39By looking at them,
09:41we can understand that
09:43they have a special Dhatu.
09:45The special Dhatu is used
09:48to select the water content,
09:50the water content of the water,
09:52and the water content of the water.
09:55The water content of the water
09:57can be selected based on the water content of the water.
10:00Now, let's see
10:02how the water content of water changes.
10:05For example, if you take two pieces of ice
10:07out of the fridge,
10:09it will be joined by two pieces of ice
10:11in both hands.
10:13Now, you have seen this incident many times.
10:15Why do we call this incident?
10:17Let's see it again.
10:19Now, what happens when the water content of the water
10:21in the ice is low?
10:23When you squeeze it hard,
10:25the water content of the water
10:27is reduced.
10:29So, to squeeze it hard,
10:31water content of the ice
10:33is reduced.
10:35What happens to ice?
10:37It is transformed to water.
10:39When you squezze it hard again,
10:41water content of the ice
10:43is reduced.
10:47So, what happens to the ice?
10:49It is rejoined.
10:51What is happening
10:53That means, during melting, ice, ice cubes, all of these are less volatile.
11:00So, in the case of all these substances, if the temperature is high, the melting point is decreasing,
11:06which we saw in the case of water, sorry, in the case of ice.
11:09That means, in most cases, they are melting at a low temperature,
11:15which we saw in the case of ice.
11:17That means, if you increase or decrease the temperature of the ice cubes,
11:22they are changing, they are becoming volatile.
11:24Therefore, it is very important to indicate the temperature of the ice cubes.
11:29In the case of any substance, when we have a standard pressure,
11:34that is, the temperature of the ice cubes, which is equal to the temperature of the ice cubes,
11:39we determine the temperature of the ice cubes.
11:42Then we say that it is the temperature of the ice cubes.
11:45Similarly, we say that it is the temperature of the ice cubes.
11:50In the same way, it is the time to say that it is the temperature of the ice cubes.
11:53In the case of ice, if it is expected, then it is equal to the temperature of an ice cube.
11:57If it is said that it is the temperature of an atmosphere, then if the temperature of the ice is increased,
12:01then the melting point of the ice will be about 0.000000,
12:06that is, three zeros, then seven, that is, triple zero seven degrees Celsius will decrease.
12:13In the case of melting, if it is said that it is the temperature of glass, aluminum, etc.,
12:18then the melting point increases.
12:19That means, in some cases it is decreasing, in some cases it is increasing.
12:22In these cases, if the temperature increases, then the melting point increases.
12:25That means, the temperature of the ice cubes which was mentioned earlier,
12:28now it is melting at a higher temperature than that.
12:30You have seen that if you look at MoM, when it melts, it can move.
12:35If the temperature increases, the melting process is obstructed,
12:38that is why the melting point increases.
12:40In the case of MoM, it is increasing by 0.0000004 degrees Celsius.
12:47You will see, in the house of the white line, the use of fuses,
12:52that fuses are made of special substances.
12:54What is special about it?
12:56No, it is made of tin and glass, and the concentration is very low,
13:01so that if a large amount of short-circuit is applied,
13:04it will be torn, and the connection will be out,
13:08so that in the house, or the equipment, or whatever is there in the house,
13:13if there is an accident or fire,
13:16the possibility of fire is saved.
13:21That means, the concentration of fuses should be low.
13:24What is done for this?
13:25In the case of glass and tin, there is a 3 to 1 ratio.
13:30In that ratio, a mixture is added, so that the concentration is low.
13:35Why is the mixture added here?
13:38So that their individual or their own concentration is less.
13:44That is why it is done.
13:46You can see, in your house, there is a small test,
13:49that there are two bowls, to see the same,
13:52and there is ice in it.
13:54So, what is done in one bowl?
13:56Salt is sprinkled on the ice.
13:58So, are the two ices melting at the same time?
14:02Now, after mixing the salt,
14:04whether the concentration of ice has increased or decreased,
14:07you have to understand that.
14:09This is a very good concept to say,
14:12because here, salt has been mixed,
14:16so, to mix the salt, you can understand,
14:19there is a change in concentration.
14:22So, for this change in concentration,
14:24this topic has been asked.
14:27As I told you a little earlier about the statue,
14:30that Pital is being carried.
14:33You can see it here,
14:35that a statue is being made with Pital.
14:37And when Pital is in a difficult situation,
14:40then its concentration increases.
14:42So, it can be easily said,
14:44that when the water is difficult,
14:46when the water is difficult,
14:48then its concentration will increase,
14:50but its concentration will not be complete,
14:52it will be like this.
14:54So, it will be seen as complete as a frame.
14:56That is why Pital is being used.
14:58As I told you earlier,
15:00that you have seen,
15:02that when the water is difficult,
15:04then its concentration increases.
15:06For example, Pital's name was there.
15:08In the same way,
15:10the question I asked you here,
15:13is that,
15:15when salt is mixed,
15:17will the concentration of ice increase or decrease?
15:22That means,
15:24you can understand from here,
15:26that when salt is mixed with water,
15:30then its concentration decreases.
15:34What does that mean?
15:36It is kept at a low concentration.
15:39That is why,
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