11th Class Physics Chapter 9 | Electrical Power | 11th Class Physics New Book 2025

[00:00:06]Assalam Walekum Da Student This is Kashi Majeed Your Physics Teacher Hope you all are well. Student Chapter Nine we are discussing and today we have to discuss electrical power. Students, before electrical power, if you saw in the previous chapters, we discussed mechanical power as powers.

[00:00:23]In which we had said that the rate of doing work is called power. Ok? The work that any object performs in a unit of time is called its power.

[00:00:33]So now if we want to see the same thing for electrical energy or want to understand the concept of electrical power here, then when the word electrical power is used in it, then what will happen is that some circuit of ours will be formed here. Ok? What will we do with the battery in this? Will connect to any circuit.

[00:00:48]And along which any one register will be R. There is a resistor R which is connected in series with A battery is connected to a source emf. Ok?

[00:00:58]Now what will you do as students? If you connect this battery with it, then you know that here if you take the direction of conventional current, it is positive terminal to negative terminal of a battery. So you will say that current will flow through this resistor R. When will the current flow? What is the potential between terminal A and terminal B? Let the potential difference be V. And what will this potential difference V be? The potential difference of this battery will be equal to V.

[00:01:23]Ok? Ok? What will be the potential difference between these terminals as much as this battery provides? There will be a potential difference. Now what is point A? This is at high potential. And what is point B? It is at low potential. So what the battery is basically doing is shifting the charges from low potential to high potential.

[00:01:39]Charges like this, if you see the current then the charges will move and come out of this resistor.

[00:01:47]What is any register here? Some sort of you may have an electrical lamp. Someone may be a fan of yours. So energy will dissipate here. Ok? Energy has been used here. And the same electrical energy that the battery provided to the charges is being used here. Now as soon as the charges consume their energy, they will come back to the battery here.

[00:02:06]So the charges are entering here at low potential. What is the negative sign representing? To low potential.

[00:02:11]So we will enter here. So the battery again will supply them energy. And after supplying energy, we will move it again in the circuit. So, please understand this thing in some unit time of the battery.

[00:02:28]What would you call the amount of electrical energy supplied to these charges by a battery in a unit of time? This will be called the electrical power of that battery.

[00:02:29]So what should we say? The rate at which the battery supplies electrical energy is called power output of electrical power. This can also be called power output. It can also be called electrical power. Whose?

[00:02:49]What will be the name of that source or battery that how many energy charges the battery is supplying in a unit time? It will be called electrical power. It is a simple concept. So what would you call its formula? Then what did the electrical power equal? Energy over time. As you saw in the previous topic. We wrote P = W over time. So here is work in the form of energy. Ok? So what will you write here? Energy over time. So what is the formula for electrical power? Energy over time. Now student, you have already defined this.

[00:03:16]I also wrote its mathematical form. Now what should I do with this result? A formula has to be made for its power. Ok? That we have to convert this formula into the form of VIR which is being used here. Like potential difference is V, current I is flowing, resistor is R. So all these things need to be in our formula so that we can do what? You can find out the power output or power dissipation of that battery.

[00:03:39]Ok? Now students, what did we do for this? All the same things that considered there is a circuit containing a battery E. Ok? Which is connected in series with the register R.

[00:03:50]What's with the resistor R? A battery is connected in series.

[00:03:52]Ok? So these things will come in our explanation here.

[00:03:56]We will make the circuit. After that, in this circuit, the same thing which I have just explained, that is, battery in the circuit. What is the battery doing?

[00:04:02]Continuously lifting charge appeals through a potential difference B that the battery is providing a potential difference to these charges.

[00:04:09]Ok? Will provide energy. Like again there are new charges, so at this potential there is high potential here.

[00:04:15]Here you have low potential. Ok? So providing high potential again to the charges with low potential. Ok? They have to be taken uphill. So you would say this is lifting a charge uphill through a potential difference V. So this is the work of the student battery, what is the battery doing to us. Ok? What will we say after that? Whose equal will the work done here be? Work Done in Moving Charge Q.

[00:04:35]Suppose she is moving the charge Q in the battery and through a potential difference, how much potential difference is she bringing between them, this potential difference, as I have said, here there is low potential, what does low potential mean, it is 0 volt, okay and high potential, like you have a 10 volt battery, then what is the difference between these two, 10 volt, so how much will this battery that you have, it will be of 10 volt, okay, so this is the work done here that work done in moving a charge q through a potential difference V, okay and what did we do with the formula of work done from electric potential, that v equal to what did you have? W over Q then W equals to what? QV Q multiply here.

[00:05:11]We had explained this in the topic of potential.

[00:05:12]So what will W come from this? V * Q V is the potential difference you have. Q What do you have here?

[00:05:20]Charge. Now students, here you will see this is the amount of energy. What is this?

[00:05:24]Amount of energy supplied by the battery. This is the amount of energy the battery is supplying to the charges. Ok? Now student, the second thing you have to see is that if you want to write this flower, then what will you get when P equals to? Work over time P = W over t which you also read in mechanical form is rate of doing work. So that's exactly what we used here. But we have to replace this W again.

[00:05:50]What value would you put on this W? W = QV so I have put this W. W = QV v * Q or Q * V whichever you want to write. Now student, what is this q over t? Please tell me. Firstly, you used w = qv.

[00:06:07]Second you have q over t.

[00:06:12]Rate of flow of charges. What is this equal to? This is not equal to the current.

[00:06:17]So what will you do? What will you put in place of this q over t? I and this V as it will come.

[00:06:22]So what will become the formula for power? P = V * I This is the potential difference.

[00:06:26]I What is here? There is current. Now students, what can you say about this, that this is basically electrical power and what has become of it? P = VI, so you have a formula. Ok? Now [nasal sound] you're going to add a line here. The power supplied by the battery is dissipated in the resistor R. So what will be the power supplied by the battery? What will you have in this register R? It will be deciphered. Ok? So in the same way, whose power deception was equal to? If the power output is equal to P = VI, then what will your power destination be equal to? It will be equal to VI.

[00:07:02]According to whom? Equivalent to the Law of Conservation of Energy. Because neither can we create nor destroy energy. But it can be converted from one form to another. So if the electrical energy that the charges had here was lost, what would you have here? If a fan is connected then the fan will convert it into mechanical work here.

[00:07:20]Ok? It will convert it into the form of heat energy.

[00:07:21]So basically one form of energy is being converted into another form.

[00:07:25]Ok? So what would you write about this? P = VI, this much energy will also be dissipating according to the law of conservation of energy. Now students, we have to make its equivalent form.

[00:07:36]Because in some cases in numericals we also have to use the relation of registers apart from V and I.

[00:07:42]Ok? The relation of potential difference must be being used. Current relation must be being used. The relation between current and resistor must be being used. So that's why we need some more formulas also. Ok? So what will we do for this? We will make some substitutions in the initial form P = VI. I will put some in it.

[00:07:59]What will you put? According to Ohm's law.

[00:08:01]Once you have to put the value of this V.

[00:08:03]Once you have to put the value of this I. Do you know what V equals two is?

[00:08:08]According to Ohm's law, V = IR.

[00:08:10]We proved this in the previous lecture. Ok?

[00:08:12]What is V equal to? IR Now if you put the value of this V here. In the first step you have to put the value of this V.

[00:08:21]What value? V = IR If you put IR * I in it then what will it become? I * I² will become int R. So this is your first formula for power. What will come to you? Its second form will be made. This form is also equivalent to this. That's why I gave the heading of equivalent form.

[00:08:39]Ok? Now student, what do you want to consider again? This is what Phula did. P = VI What did you do first? V is the value of the put.

[00:08:47]Now you will write V as it and put the value of I.

[00:08:51]Now what is the value of I? V = IR then what is I equal to? V over R So you put V over R in place of this I. Now what will become of student V * V? V² over R so this power will become equivalent to your third form. So, we will also use these forms in numerical problems, Insha Allah.

[00:09:11]So here you can say what will be the unit of this power? You have also read this in previous classes that what is the unit of power you have? Watt is. Then you can also define 1 watt as whether the power is dissipated or power supplied. You can explain it in both senses.

[00:09:27]So you would say the power dissipated in the circuit will be 1 W. When is the power? It will be 1.

[00:09:33]When will the potential difference be? will be 1 volt.

[00:09:37]And how much current should be maintained because of that? 1 ampere. 1 ampere current is maintained in that circuit due to the potential difference of 1 volt. So in that case, what will be the power of the source you have? Will it be 1 or how much power will you have that is being dissipated along the resistor? There will be 1 vat. So this was your topic electrical power. Hopefully you have understood it as it is. See you in the next lecture, Inshallah. Allah Hafaz.

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