Do subscribe to Ekeeda channel and press bell icon to get updates about latest Engineering, HSC and IIT-JEE Mains and Advanced videos.Hello Friends,In this video we are going to study that what is a resistance how we can define it and what are the ways in which the resistance can be expressed and what are the factors on which the resistance depends so let us start with our topic. Resistance is the property of a material which opposes the flow of current through the conductor okay means if we are having an electrical Network and in that electrical Network a material or a conductor is connected now this conductor there will be a flow of current in the electrical circuit so it is the property of the material which is connected in the network that which opposes the flow of current through that material so we can define the resistance as the property which opposes the flow of current you not this resistance if we want to measure the resistance then this resistance can be calculated with the help of the own you so according to Ohm’s law the resistance is defined as you suppose V is the voltage across that material which is connected in the electrical circuit and I is the current flowing through it so resistance is defined as the division of the voltage and the current when the temperature is kept as or when the temperature is treated as a constant property okay so this formula is defined means this Ohm’s law is valid only when we consider temperature as constant so this resistance through this expression or through the old slow we can calculate the resistance by dividing the voltage and the current now when the temperature it is not treated as a constant entity then the resistance can be calculated as so when temperature is not constant then suppose Stephen is the initial temperature and t2 is the final temperature at Stephen we have the resistance as argon and at t2 we are having the resistance as r2 okay then this resistance r2 for we can say the change in the resistance we can calculate by the formula r2 equals to R 1 1 plus alpha T 2 minus T 1 okay so R 1 is the initial resistance of the material at the temperature T 1 degree Celsius and when the temperature is changing the resistance will also change so suppose that after the temperature T 2 degree Celsius the resistance of the material is R 2 so R 2 can be calculated as R 2 equals to R 1 1 plus alpha T 2 minus T 1 now this T 2 minus T 1 it can be written as T which is the difference in the temperature and alpha is the temperature coefficient of the material okay so one of the formula for calculating the resistance was through the Ohm’s law R equals to V by I another formula if we want that if the temperature is not taken as constant we can calculate the resistance by using this formula now there is another formula for through which we can calculate the resistance in that formula we are expressing the resistance in terms of the physical dimensions of the material you so the formula is R equals to Rho L by a where Rho is the resistivity of the material L is the length of the material and a is the cross-sectional area of that material so according to that formula R is equals to Rho L by a ok this is the formula now in this formula Rho is the resistivity or we can say it is the specific resistance l is the length of the material and E is the area so through that formula you can see that our is directly proportional to the resistivity R is also directly proportional to the length of the conductor and also R is inversely proportional to the cross-sectional area so the formula becomes R equals to Rho L by L so as the specific resistance or the length of the material increases the resistance also increases and if the cross sectional area increases the resistance decreases okay now the resistance it can be because these are the formulas through which we can calculate the resistance so the unit of measurement of this resistance is holes so if you want to measure the resistance it is measured or the unit of measurement of resistance is ohm you so suppose the resistance of a material is to the value is the numerical value is 2 so we are going to expresses like 2 ohms this is the symbol for the ohm now this value can be ohms kilo ohms mega ohms okay in this way we can have the different values of resistance for different materials now if we want that we have a good resistance then there are some properties which are desirable in the material which through which the resistor is or the resistance is constructed so what are these properties let’s see you so the properties are that the value of the resistance should not change with time okay like if we are given that this resistances of the value 2 ohms so the value of that resistor should not change with time click like if the resistance is not in use for a long period its value D grapes so this should not happen if I want that our resistor should be a good quality now also the resistor should have low temperature coefficient of resistance okay also if the resistivity should be high so that the size of the resistor is is small okay because the Press’s tivity aside then the resistance is high and the size of that resistance becomes smaller you also the properties are like the material of that resistance resistor like the material which we are using for making the resistor it should have a resistance to oxidation corrosion and the moisture effects so that the resistor do not get damaged due to these factors also the material should have no thermoelectric EMF against copper so these are the properties which are desirable for the material which we are using for making a good resistor okay now there is no single material which can have all these properties so we use the resistor according to the application like for any application if you want that this property low temperature coefficient of resistance is required so we are going to use that material which is having no temperature coefficient of resistance okay so according to application we will choose the resistance for that particular function okay now as I have told that this resistance it is measured in terms of ohms so the value of the resistance it can vary from few ohms to several mega ohms and this resistance it is used as the most basic element of the electrical and the electronics engineering for the measurement of this resistance we have various devices various methods are used for the measurement of the resistance devices like we can use multimeter for the measurement of resistance in the multimeter we have to to connecting leads so we are going to place the two leads across the two ends of the resistor the resistor it comes in the shape of this we have several lines over this resistor there are different colors of the resistor and these four bands on the resistor they are used for calculating the value of the resistance okay there is a specific formula for calculating the value of that resistance so to measure the value of that resistance we can use multimeter the multimeter they can be like analog multimeters or digital multimeters and there are various methods also which are used for the measurement of the resistance so in this video P study that what is the resistance how it is expressed we see different formulas R equals to V by a according to the Ohm’s law then R equals to Rho L by a which is expressed in terms of the physical dimensions of the material and also we express the resistance that if we can calculate it r2 equals to R 1 1 plus alpha t like if the temperature is not constant then we can use this formula and what is the unit of measurement of the resistance that is homes so I hope that this topic what is a resistance is clear to you thank you

## 5 Comments

How can we calculate the resistance if we have multi reading of temperature as follows t1,t2,t3,…,tn

Thank you for the useful lecture

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please explain about ohmmeter, megger and earth tester in detail