 Hello and welcome to the session. In this session we are going to discuss problem solving using dimensional analysis. Dimensional analysis is also called factor level method. It is a problem solving technique of calculating physical quantities in which units are included and are treated in the same way as numbers. In this method we use units and the conversion factors to solve a problem. Let us now discuss some of the terms used in problem solving. The first term that is commonly used in problem solving using dimensional analysis is initial unit. As we have to convert one unit into another, so initial unit is the unit which we have to convert. Initial units can be one or more than one. For example, in converting kilometers to meters the initial unit is kilometers and here we see that there is only one initial unit. In converting kilometers per hour to meters per second there are two initial units that are kilometers and hours. The next term is desired units or wanted units. These are the final units that we want to obtain. The next term is unit path. This is the series of conversions used in order to obtain the desired unit. The next term is conversion factors. Each conversion factor is a ratio of units that equals one. For example, from the conversion kilometers to meters one kilometer is equal to thousand meters we have two conversion factors. One kilometer upon thousand meters or thousand meters upon one kilometer because one kilometer upon thousand meters is equal to one and thousand meters upon one kilometer is also equal to one. We will use the following steps to solve problems using problem solving method of dimension analysis. The first step is to identify the initial and desired units. The second step is to identify the unit path from initial to desired unit. So, in the unit path we begin with the initial quantity which is written here with units. Multiply it with conversion factors that will be written in these blank spaces and we obtain the desired quantity with units. Now, our next step is to write the unit path using equivalence as conversion factors to obtain desired units. Step is to treat units as numbers. It means we set up the problem so that units are cancelled and we are left with desired unit. Let us consider the following example. How many seconds are there in three days? Our first step is to identify the initial and desired units. In this question we have to find the number of seconds in three days. It means we have to convert days into seconds. So, here we have the initial unit is days and the desired unit is seconds. Step two is to identify unit path. In this case we will have linking units that is to convert days into seconds. We will first convert days into hours, then in minutes and then in seconds. So, here the initial quantity is three days and the desired quantity will be in seconds and the unit path will be written like this. The third step is to write unit path using equivalence as conversion factors to obtain desired unit. Now we know one day is equal to 24 hours, one hour is equal to 60 minutes and one minute is equal to 60 seconds. From one we have one day upon 24 hours is equal to one and 24 hours upon one day is equal to one. From two we have one hour upon 60 minutes is equal to one and 60 minutes upon one hour is equal to one. And from three we have one minute upon 60 seconds is equal to one and 60 seconds upon one minute is equal to one. We will choose those conversion factors so that all other linking units and initial units cancel out and we are left with the desired unit that is seconds. So we have the following unit path. See here we first convert days into hours using the conversion factor 24 hours upon one day. Then we convert hours into minutes using the conversion factor 60 minutes upon one hour and lastly we convert minutes into seconds using the conversion factor 60 seconds upon one minute. Our next step is to treat units as numbers that is to cancel the units and terms so that we are left with only desired units. If we try to cancel out the linking units and the initial units that is days cancel with days hours cancel with hours minutes cancel with minutes. We obtain the desired unit that is seconds. So now three days is equal to three into 24 upon one into 60 upon one into 60 upon one seconds. That is equal to 259,200 seconds. Therefore there are 259,200 seconds in three days. Which is the required answer? This completes our session. Hope you enjoyed this session.