SCIENCE PAPER 1(PHYSICS)- 2019 SECTION C- ECZ SYLLABUS

welcome to eagles concepts learning in this video we're going to take you through our science paper 1 2019 section c so we'll begin with question c one the question is a spring with its upper end fixed hangs vertically alongside emitter row the lower end of the spring gave the following readings in temple c 1.1 when various masses were hung from it so there you can see the table we have barriers recordings here mask in cages readings the applied force and the extension okay so b says copy and compute the table for the values of the applied force n and the extension centimeters produced c draw a graph of applied force against extension on the ground paper formats d on the graph show the elastic limit one marking so the total of each question is 10 max you are only required to choose two out of the three questions provided and i can assure you all the three questions at least two for one will be on graphs so pay attention as we take you through the graphical way and the other question so the solutions the first question says now folks law states that the extension of a loaded stream is directly proportional to the load causing extension provided that the elastic limit is not exceeded so just for stating this one you have your one mark now let me just explain a bit about elastic limit so elastic limit as you are putting your masses on the spring there the spring is expected that it will be extending linearly at the same interval so the interval will be the same for example if the zero kg mass here uh if the 0.02 kg mass extended the spring by 2 we expect that 0.04 kg also extended by what by 4 and so on and so forth that's what it means so now this elastic limit here when it's when the spring reaches this point it means that it can no longer return to its original position when it reaches this point meaning when you go beyond this point the spring is going to be permanently destroyed that's what it means meaning hooke's law will no longer be obeyed beyond this point as you will see when you brought the graph okay so let's go ahead b was simply saying uh so b was simply saying complete the table so now this is what you're going to do so now this column is for the masses so this one it simply shows that this one 0 kg it means they didn't put any mass on the spring so this is the original mass priority of the spring so after they were they had to put a 0.02 kg spring then it had gone to 12 centimeters now for for us to fill in the forces here it means we are just converting from kgs to newtons and the way we convert from kgs to newtons we use the formula w is equals to m g now this w simply means weight now because the weight is in newtons it simply means that it is also a type of a force so this one is neutrons the m is the mass which is in cages and the g the g here is uh the acceleration due to gravity and this one can be given as 10 newton per kg so 10 newton per kg that is the value of g here on earth so if we want to convert from mass and taking it to newtons it means we are simply going to multiply these kgs by 10 so that we have our value so multiplying 0.02 multiplying by 10 we are going to have 0.2 newtons okay so using this formula meaning we are going to say the first one the first one is this newton here since we know that this one is newtons and this one is in cages so let me just give an example of the test one so we are going to say the newton [Music] so this is 0.02 pages multiplying with 10 uh newton a kg okay 10 neutron packaging so that these kgs and that cages for one remaining then when you multiply 0.0 to multiply by 10 you're going to just move one distance which is giving you that one so you do the rest you do the rest of the similar way so 0.04 times 10 simply give us 0 um this one will give us zero point six so we're saying zero point zero six multiply by ten then we go to zero point zero eight multiply by ten this one is giving us zero 0.8 and this one also they already did this one for us so it maintains okay now going for uh these other parts extension now extension is given by the formula so i'll just write e for extension okay extension uh is equals to uh extension is equal to new length so i'll just write new length okay so new length uh minus so that is the formula new length minus the original length so original length i'll just write it that's it n o so that's what it means so extension will always be given by new length minus the original length so in this case we are saying the original length is 10 here because notice that before anything was put the reading was 10 meaning this is the original length of the spring so the new length in this case after they put in 0.02 the new length became 4.0 so to find this value we are simply saying 4 minus 10 and define the value is 2. then we go to the next it will also be 14 minus 10 which is going to be 4 then 16 minus 10 is going to be 6 then 17 minus 10 this one is going to be 7 so that is how you fill in the table remember extension here is given by the formula so extension will be given by e is equal to this one i'll write as in with a subscript e as [Music] which means original length so when you use this one across everything you are going to fill in the table like this and there you have your four marks and here you have your one mark so already that is your five marks okay we proceed the next one they said we should now plot a graph so now uh a few things that you need on the graph is you need a title so okay now using these values you need to plot the graph so let me just take you back to the question here it says on a graph of uh on a graph of applied force against extension draw a graph of applied force so here it is applied first against extension so this one is your formula and this one is your title so the one which they request you to do is actually the title of the graph now this one is the quantity which has been mentioned there it forms the y axis okay forms the y axis and then the other quantity which is mentioned last this one from the right x-axis so we know that in this case applied force will be on the one where the extension will be on the x so let's look at that so we are saying this table look at it our applied force this one is our y-axis this is our y and this one our extension so that is how you figure out which one is the x and which one is the y so having figured out these values then we are going to plot okay so the first thing that you need is the title write the title graph there okay so you can move the diagonal and align it so type the graph then somewhere there you have to write the scale so you write the scale of your graph like that even the title you write i'm not saying you write the name right on the graph and underline that side then you figure out the scale so the scale in this case we're going to check it out okay since uh this one has been counted as 0 0.2 so here we can just harvest it on the x-axis write something like on the x-axis okay so on the x axis you can use a scale or row uh let's say two centimeters two centimeters to represent okay i'll show you on the next diagram how it is supposed to be done for the graph here so that one there you can draw two centimeters to represent zero point one so you draw this one as your y-axis okay then this other one is going to be your x-axis so that is the y-axis you use a roller to do this draw your x-axis like that then the next thing now which you notice is you are going to be saying this one let's see this is one two three four five six seven eight okay so here on the x-axis two centimeters will represent one so this is one two three and this one will be four the next one will be five and the next one is six from there we go to seven from there go to eight okay then here we're just going to count now this is 0.1 so it's that so you figure out how we are supposed to do it this is 0.1 0.2 [Music] zero point [Music] zero points this one [Music] by [Music] extension there so extension in same thing [Music] so just for doing this they are marks so this 0.5 0.5 plus 1 0.5 0.5 so already the next thing that you're going to start doing you're going to start plotting so the next thing here we have zero comma zero then the next thing we have is two comma two okay so uh this one we have uh sorry it's two comma zero point two so two comma uh zero point two then the next one is four comma uh four uh 0.4 [Music] six [Music] [Music] is the [Music] so point five for my right now the one here and the seven from five okay just count this is one two three four five six seven four five so as you can see using your ruler here you can really tell to say this one here is a straight line so up to somewhere there this is a straight line it was obeying me then from there [Music] get okay so you are done with your brush now you have leveled everything and that is that [Music] this one here is a mark there then also on the scale there's a mark on your title there is a mark [Music] here is a match then also for labeling your axis this one is supposed to be the x-axis there's a match and you can get the whole format never forget these rules on how we deal with graphs in science okay c2 the question reads two lamps s and t are of resistance 200 ohms and 300 ohms respectively are connected in series with a 240 volts mains as shown below so this one first uh first things first this one is a series uh connection it's a serious type of a security so in a series type of the circuit here are a few things that you are supposed to know you are supposed to know that current which is given by the symbol i so there are rules distinguished rules so current is the same throughout the circuit is same so current is the same throughout the circuit and then number two you are also supposed to know that uh voltage uh voltage total voltage is equals to vt which is equal to v1 plus v2 now this simply means that the voltage is not the same meaning the voltage in here is different from the voltage here that's what it means so to find this total voltage we need to add the voltage in here for the voltage and we are going to know the total voltage but the current is the same so if i measure current here current there current there current there current anywhere in the security [Music] resistance rt is just given by rit because [Music] so these are the main rules that i thought people should know about and content that you know them before you can start the calculations so the first one they're saying calculate the current at the point b so the first thing that you're supposed to do here of course is collect your data so in collecting your data you are going to know that the bt here so collecting let me just collect the data right here so that i'm just collected right here where people can see so data we have the vt the total voltage here will be given as our 240 points so we have our 240 volts then rt okay so now what we have been given here we have error is meaning resistance in the s which is equal to 200 ohms okay so this one is 200g ohms then we are putting the error error in the t not the total resistance but just error in this uh so this one which was equal to 300 ohms so this is the data that will be given then the first question is asking us to calculate current at g so the current i here we don't know now because current is the same in the second meaning the formula which says current current is equal to so a1 here current is equals to voltage over resistance that is a refinement of current exposed voltage resistance now since current is the same here we first need to know the total resistance so total resistance here rt will be given the formula we've already figured out that it's r1 plus uh plus r2 so we're just going to add 200 plus 300 so the 200 plus 300 give us the 500 ohms so you add 200 ohms plus 300 ohms 200 plus 300 ohms this one will give us our rt as 500 ohms so this is what we have so therefore current so the answer for a1 therefore current is equals to uh current is equals to the voltage which is 240 volts divided by our 500 here so punch on the calculator there and we have our value as 0.48 so we have zero point four eight amps units are very important so this is 0.4 amps and we have our answer there okay a2 is simply saying uh calculate the potential difference across in our potential difference across s so now potential difference is the same as the voltage and we know that voltage will be given by the formula if you just change this formula so voltage will be given by voltage because i are meaning current multiplied by resistance now we know that current is the same okay current is the same so we are going to use the same current we have found there which is zero point four eight amps and then multiplied [Music] 300 ohms then our answer here is going to give us the answer is going to give us 96 votes and six words and that is our potential difference okay we go to question b from this space here question b this one simply says uh draw a circuit diagram showing resistance s and t connected to me parallel okay so in parallel now you need to know okay we have that one the positive and the negative then we are going to have a situation very nicely so we're going to have a situation like that then [Music] something like this [Music] what you expected now we have put it in parallel so this one is the s and this one using the t so this is how you can actually throw these things and then the beauty about this thing is that they will have separate switches this one make sure you can put a switch somewhere here so you put a switch somewhere here then this other one also you can have a switch somewhere here so these separate switches so this one is how you can draw the paradigm circuit okay so it was saying draw a circuit diagram showing resistance s and dt connected in parallel just stand up and see using the diagrams in 2b calculate the current through lamp s and lampton okay the current through lamp s and lambda now like we were saying uh in the in the parallel circuit there are also rules one of the rules is that voltage is the same throughout so voltage is the same throughout okay so here since we are given a voltage of 240 the voltage of 240 volts it means that s there was 240 also through bounty there was also 400 240 volts okay so this one it has a resistance of uh to s 200 so here resistance is giving us 200 and [Music] it means that to find the current because current is not the same okay so current here is not the same so the current is so we are simply going to say uh to find the current you know that current uh is given by voltage over resistance this one is equal to so the voltage is the same everywhere so it will be 240 watts 240 volts divided by 200 and our answer for this one punching from the calculator is going to give us 1.2 amps so one point two arms okay then we go to the second one also current because so this is currently s and here we 240 divided by 300 ohms so this is 300 pounds what's there there okay so this one is going to give us 240 divided by 300 is giving us zero pointy a g amps so your phones your answer there next they are saying find the total resistance with the security now for the total resistance narrative it has got its own formula for the parallel which is given by 1 over 1 plus 1 over arrow 2 and so on and so forth but if there are only two resistors if there are only two resistors you can use the formula r2 is equal to r1 arrow two over arrow one plus arrow two so in this case it will be equal to our arrow one which is two hundred so that is 200 multiplying with 300 over so multiplying with 300 over 200 [Music] plus 300 okay 300 and the answer in this situation punching on the calculator we do give us 120 ohms so this is 120 ohms and there we have our final answer okay so the question is give two reasons why lamps are preferably connected in parallel homes okay so the reasons are very simple here so number one i can say number one reason is that number one damage caused in one power cannot affect the other bow the number two is that parallel circuits they have independent switches so parallel circuits have independent switches the number one is that the damage caused in one cannot affect the other power like in the series okay so uh go to the next question of section c which is c3 and the question reads figure uh figure c 3.1 below the diagram showing the volume [Music] before reaching the horizontal ground so this is the boiling point that is being shown here and it is moving from up all the way up to down so the changes in gravitational potential energy of the body as it rolls down to the horizontal ground as shown the first question says state the law of conservation of the energy now the law of conservation of energy simply states that energy can never be created nor destroyed it can only change from one form to another okay b using the values in table c 3.2 draw a graph of potential energy against time okay so it's very important that you understand that this one here graph a graph here a graph of potential energy against time that is the title of the graph now not only is it the title of the graph but it is also trying to show us something here so not only is it the title of the graph but it is also showing us uh which quantity to put on the x-axis and which quantity to put on the y-axis so now the first one which is mentioned is always on the white and the last one to be mentioned is always on the x so that is the general rule that you can follow so thereafter you can figure out the correct scale to use so like in this instance let's look at this graph okay so here that's the title of the graph uh the graph of a potential energy against time then we also need now to have a scale by the side here that is the first thing that is going to be open this time in the graph so you can write the scale as on the x axis okay on the x-axis so you write it like that on the x-axis two centimeters two centimeters is representing two centimeters is representing one second okay which means that you'll be counting in one one one so one plus one two plus one three plus one four so that is what it means then on the y-axis right on the y-axis we say two centimeters is representing one job so this one using one job and there we are done with the scale so we already have a mark for that and the map for that so you also write the axis name here and the axis name there so you have a mark for that and the mark for that then you are going to approach your graphs then you're going to plot your coordinates there so you have this coordinates here you also have that coordinate there also have uh this coordinate there and you have this code right there according to actually given to the table and then you finally have the five comma zero so you connect it with the straight lines there okay so we go to the next question which says calculate the height h of the inclined plane when the potential energy was nine joints if the mass of the ball was 900 grams so data collection here if we can collect the data so look at that that will be given so from the data that will be given here we have uh image itself so we have potential energy which is equals to nine joints and from there we also have the mass which is equals to 900 grams now we have to complete this one from grams to gauges [Music] i think this is something that we know right now so this one will give us 0.9 kgs okay so that's become cages and thereafter what else do we have okay so we have the mass we have the sha then they are asking for a height so h is equals to question mark so here the formula to use was potential energy p e is equals to m g h so meaning here we have the potential energy which is nine joists so we're writing nine jaws equals two uh that is the mass now is zero 0.9 kgs multiplying with so 0.9 kgs multiplying with multiplying with so the g here is 10 newton pkg so this is 10 newton per kg multiplying with the h so here we are going to have nine joists is equal to so 0.9 times 9 9 times h that gives us 9 h so we divide by 9 and this side we divide by 9 and we finally have our h as h is equals to uh one meter so our height is actually one meter this question says using the graph estimate the kinetic energy of the volume ball at so this one you just go to time 2.5 seconds which is here draw a dotted line where it meets the slope here you will decide and pick up the value which was it one two three four okay so this was it four point five joints that is in our answer then the next question says we should also find the image at four seconds so we go to the four seconds draw a dotted line like that and get the value here which was actually one point eighty joints and that is how you deal with the graphical work so make sure you have that of your graph have the scale level the axis and you choose the appropriate skill to ensure that your graph at least big enough it is feeling about 75 of your work thank you for listening to this video till next time do not forget to subscribe