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GCE A-levels since their inception in 1951had not been criticized as much as they are being now ..this is mainly due to government pressure on schools to achieve high examination results has led them to coach students to pass the examination rather than understand the subject. And most importantly As the cost to an examination board of changing a subject's syllabus is high they are reluctant to do so, which leads to a lengthy period over which exam questions are similar, allowing targeted teaching to anticipate the questions. But who CARES !!! as some of our friends here say.. ‘In god we trust and rock we must’ http://www.twitter.com/bineetojha bineetojha
Now I’ve compiled this material for the Practical assessment of physics . 9702 Physics paper 3
Question 1:
First you have to measure something and judging by the space provided you have to show the evidence that you have taken repeated readings and averaged them out say you have to measure the diameter of a sample of wire so using the micrometer screw gauze take 3 readings in three different parts along the length of the wire and show d=(d1+d2+d3)/3 ..and show the value calculated, in the space which says d=………..
And present the data to the appropriate number of significant figures so that if reflects the least count of the device being used..as 0.01mm for micrometer screw gauze, o.1 cm for meter rule ..and please represent your date in the SI unit..meter for length, radius e.t.c
The second question involves some calculation ..and are not credited..usually a formulae is given and u are required to calculate something..as calculate the cross-sectional area of the wire. Then a setup of the instrument is required and a figure is given for help. Then it says u to measure something out of the equipment set-up. Say length of the wire between two crocodile clips. It is obviously measured with a meter rule to take care of the least count
Then it says to repeat the procedure and get six different sets of data in a table ..students often have this thing out of their mind that the presentation is important ..and CIE in its examiner’s report terms such students as ‘weak candidates’ ..so first thing first…know how many variable u have to measure and/or calculate so you could draw appropriate columns ..use the full space provided form about 2 mm of the left most ‘don’t write in this area’ to 2mm of the bar of ‘for examiner’s use’ first draw a rectangle covering whole of the space and then draw a upper row relatively wide..then draw a narrow column headed S.N then draw equal sized columns for the variables then draw equal sized 6 rows below the heading row the column heading carries one mark ‘quantity/unit’ then your range should cover almost whole the ..say length of the wire in this example I’ve been using and this is your independent variable . But it could be something else too.. so take care of it .then it requires to measure the dependent variable ..as if you have to measure time period of an oscillating pendulum ..make sure that the amplitude is not greater then 5 cm..then display 3 sets of data in 3 small columns for 10 oscillations 10t1 ,10t2 , 10t3 and show in a separate column the calculated value of ‘t’ stating the formula in the column heading ..again significant figure of the raw data should represent the precision of the instrument used..and s.f of any calculated value from those data should be in same or one more s.f correct calculation carries one mark ..and six sets of data carries 5 marks ..and do not panic if your data has some flaws..inform the supervisor and if he gives replacement of some instrument carry on or if he doesn’t ..hit him with the same instrument !!! just kidding..any type of malfunctioning of instrument will be reported to cie and u are not penalized for it as your practical skills are being assessed .
Then it requires u to plot a graph ..i personally recommend plotting a landscape graph with the paper rotated 90◦ anti-clockwise the two advantages that u’ll have is that the indeoendent variable which has far less degree of error is on the longer axes of 12 grids while the dependent value’s , with significant amount of erroer, on the shorte axes of 8 grids and also the best fit line will be close in y-direction . Axes :
Sensible scales must be used. Awkward scales (e.g. 3:10) are not allowed.
Scales must be chosen so that the plotted points occupy at least half the graph
grid in both x and y directions. and I suggest ..as most of the p5 students must have noticed in the graph question, make first scale marking one interval unit less than the least value and make the last marking one interval unit more than the greatest value
Scales must be labelled with the quantity which is being plotted with units.
Scale markings should be no more than three large squares apart so to be on the safe side label all the marks.
All observations must be plotted on the grid. blobs (points with diameter > 0.5 small square) are not accepted so I recommend pointing a gentle ‘tub’ with a sharp lead pencil..and encircling with a soft pencil. Work to an accuracy of half a small square.
Best fit line must have the balance of at least 5 points which means u can ignore any one point whish does not fit into a trend . There must be an even distribution of points either side of the line along the full length our sir used to call the best fitline ‘INSAAF WALA LINE’ which meant line doing fair treatment to all the points ..so the vector displacement of the points from the line should cancel out to zero . Lines must not be kinked.lines thicker than half a small square are not accepted so I recommend a sharp lead pensil and a transparent ruler for this job. All points in the table (minimum 5) must be plotted for this mark to be scored. All points must be within 2 cm (to scale) in x direction of a straight line. The hypotenuse of the triangle used to find the gradient must be at least half the length of the drawn line. Both read-offs must be accurate to half a small square and sensibly quoted on the graph and in the calculations as well. Intercept Either: Check correct read-off from a point on the line, and substitution into y = mx + c. Read-off must be accurate to half a small square. Or: Check read-off of intercept directly from graph. then a calculation follows which requires u to substitute the values obtained in previous calculation of gradient and intercept . a method mark and a accuracy mark for the new calculated value. [20]
Question 2:
The first part says you to measure something ..no repeated reading required and a consistent unit must be quoted with the appropriate no. of sf. u will not be credited if u take a help from the supervisor. The second part usually has something more ‘vulnerable’ to error be measured so in which case a repeated reading is required..same method as in question 1 ..then a calculation of percentage uncertainty follows..so usually the absolute uncertainty is the the least count of the device but in most cases it’s greater..as measuring the time period with a stopwatch of least count 0.01 s would not make any sense if u quote it exactly as 0.01..because the human reaction time is greater..so the mark scheme allows a range of absolute uncertainties ..and take a sensible value of your one ..and repeated reading reduces the range to half..so take care of it and a correct method of finding the percentage uncertainty should be used ..as u might be familiar with it in the calculating ur percentage marks..
then an expalanation may be asked for how u used this apparatus to ensure that the measured value was accurately measured ..as in o/n 09 32 ..so u can draw your modified arrangement in the diagram just above it..or a simple explanation will do. Now 2 records of something is required for two credits of-course then a calculation with those two read-offs then an alteration in the recorded value..and a new calculation..then a relationship is suggested with those calculated values and a value ’k’ ..so calculation of two different ‘k’ ,in appropriate sf, is required..one for each set of read-offs then a justification of the sf used in ‘k’ is required whish should be linked with the sf in calculation of read-offs ..then a valid conclusion based on the values of ‘k’ is required ..in which I suggest a suitable criterion is to calculate the percentage difference between the values of k ..calculate the difference and then the percentage of that difference with respect to the first value of k .
Then the most annoying ..or shall I say..most interesting part ..describing four sources of error and suggesting the possible remedy..and beware of this in the second question.. ‘You may suggest the use of other apparatus or different procedures.’it does not mean that u can change the basic procedure ..so have it in your mind that why this experiment is being done for?? ..usual points that can be included in the first points are: Two readings are not enough (to draw a conclusion.) to which a possible suggestion is: Take more readings and plot a graph/calculate more k values (and compare). Vague reference as: Few readings. Take more readings and calculate average. Only one reading Are not credited !! this point could not have been pointed by students ..not me at least so our CIE ..grants this 2 marks FREE everytime !! but the other sources of error should be pointed by u while you are doing this experiment..and one sensible way of doing it is that u can compare it with the experiment carried out in question 1 and ..notice the major flaws in this procedure so suggest an error and the possible METHOD for its elimination..as the second part (suggesting..) usually carries four method marks with it. [20]
So 40 marks are all yours..and thank me if you liked it..because your gratitude is the fuel !!
Hari om tadsat !!
Now I’ve compiled this material for the Practical assessment of physics . 9702 Physics paper 3
Question 1:
First you have to measure something and judging by the space provided you have to show the evidence that you have taken repeated readings and averaged them out say you have to measure the diameter of a sample of wire so using the micrometer screw gauze take 3 readings in three different parts along the length of the wire and show d=(d1+d2+d3)/3 ..and show the value calculated, in the space which says d=………..
And present the data to the appropriate number of significant figures so that if reflects the least count of the device being used..as 0.01mm for micrometer screw gauze, o.1 cm for meter rule ..and please represent your date in the SI unit..meter for length, radius e.t.c
The second question involves some calculation ..and are not credited..usually a formulae is given and u are required to calculate something..as calculate the cross-sectional area of the wire. Then a setup of the instrument is required and a figure is given for help. Then it says u to measure something out of the equipment set-up. Say length of the wire between two crocodile clips. It is obviously measured with a meter rule to take care of the least count
Then it says to repeat the procedure and get six different sets of data in a table ..students often have this thing out of their mind that the presentation is important ..and CIE in its examiner’s report terms such students as ‘weak candidates’ ..so first thing first…know how many variable u have to measure and/or calculate so you could draw appropriate columns ..use the full space provided form about 2 mm of the left most ‘don’t write in this area’ to 2mm of the bar of ‘for examiner’s use’ first draw a rectangle covering whole of the space and then draw a upper row relatively wide..then draw a narrow column headed S.N then draw equal sized columns for the variables then draw equal sized 6 rows below the heading row the column heading carries one mark ‘quantity/unit’ then your range should cover almost whole the ..say length of the wire in this example I’ve been using and this is your independent variable . But it could be something else too.. so take care of it .then it requires to measure the dependent variable ..as if you have to measure time period of an oscillating pendulum ..make sure that the amplitude is not greater then 5 cm..then display 3 sets of data in 3 small columns for 10 oscillations 10t1 ,10t2 , 10t3 and show in a separate column the calculated value of ‘t’ stating the formula in the column heading ..again significant figure of the raw data should represent the precision of the instrument used..and s.f of any calculated value from those data should be in same or one more s.f correct calculation carries one mark ..and six sets of data carries 5 marks ..and do not panic if your data has some flaws..inform the supervisor and if he gives replacement of some instrument carry on or if he doesn’t ..hit him with the same instrument !!! just kidding..any type of malfunctioning of instrument will be reported to cie and u are not penalized for it as your practical skills are being assessed .
Then it requires u to plot a graph ..i personally recommend plotting a landscape graph with the paper rotated 90◦ anti-clockwise the two advantages that u’ll have is that the indeoendent variable which has far less degree of error is on the longer axes of 12 grids while the dependent value’s , with significant amount of erroer, on the shorte axes of 8 grids and also the best fit line will be close in y-direction . Axes :
Sensible scales must be used. Awkward scales (e.g. 3:10) are not allowed.
Scales must be chosen so that the plotted points occupy at least half the graph
grid in both x and y directions. and I suggest ..as most of the p5 students must have noticed in the graph question, make first scale marking one interval unit less than the least value and make the last marking one interval unit more than the greatest value
Scales must be labelled with the quantity which is being plotted with units.
Scale markings should be no more than three large squares apart so to be on the safe side label all the marks.
All observations must be plotted on the grid. blobs (points with diameter > 0.5 small square) are not accepted so I recommend pointing a gentle ‘tub’ with a sharp lead pencil..and encircling with a soft pencil. Work to an accuracy of half a small square.
Best fit line must have the balance of at least 5 points which means u can ignore any one point whish does not fit into a trend . There must be an even distribution of points either side of the line along the full length our sir used to call the best fitline ‘INSAAF WALA LINE’ which meant line doing fair treatment to all the points ..so the vector displacement of the points from the line should cancel out to zero . Lines must not be kinked.lines thicker than half a small square are not accepted so I recommend a sharp lead pensil and a transparent ruler for this job. All points in the table (minimum 5) must be plotted for this mark to be scored. All points must be within 2 cm (to scale) in x direction of a straight line. The hypotenuse of the triangle used to find the gradient must be at least half the length of the drawn line. Both read-offs must be accurate to half a small square and sensibly quoted on the graph and in the calculations as well. Intercept Either: Check correct read-off from a point on the line, and substitution into y = mx + c. Read-off must be accurate to half a small square. Or: Check read-off of intercept directly from graph. then a calculation follows which requires u to substitute the values obtained in previous calculation of gradient and intercept . a method mark and a accuracy mark for the new calculated value. [20]
Question 2:
The first part says you to measure something ..no repeated reading required and a consistent unit must be quoted with the appropriate no. of sf. u will not be credited if u take a help from the supervisor. The second part usually has something more ‘vulnerable’ to error be measured so in which case a repeated reading is required..same method as in question 1 ..then a calculation of percentage uncertainty follows..so usually the absolute uncertainty is the the least count of the device but in most cases it’s greater..as measuring the time period with a stopwatch of least count 0.01 s would not make any sense if u quote it exactly as 0.01..because the human reaction time is greater..so the mark scheme allows a range of absolute uncertainties ..and take a sensible value of your one ..and repeated reading reduces the range to half..so take care of it and a correct method of finding the percentage uncertainty should be used ..as u might be familiar with it in the calculating ur percentage marks..
then an expalanation may be asked for how u used this apparatus to ensure that the measured value was accurately measured ..as in o/n 09 32 ..so u can draw your modified arrangement in the diagram just above it..or a simple explanation will do. Now 2 records of something is required for two credits of-course then a calculation with those two read-offs then an alteration in the recorded value..and a new calculation..then a relationship is suggested with those calculated values and a value ’k’ ..so calculation of two different ‘k’ ,in appropriate sf, is required..one for each set of read-offs then a justification of the sf used in ‘k’ is required whish should be linked with the sf in calculation of read-offs ..then a valid conclusion based on the values of ‘k’ is required ..in which I suggest a suitable criterion is to calculate the percentage difference between the values of k ..calculate the difference and then the percentage of that difference with respect to the first value of k .Then the most annoying ..or shall I say..most interesting part ..describing four sources of error and suggesting the possible remedy..and beware of this in the second question.. ‘You may suggest the use of other apparatus or different procedures.’it does not mean that u can change the basic procedure ..so have it in your mind that why this experiment is being done for?? ..usual points that can be included in the first points are: Two readings are not enough (to draw a conclusion.) to which a possible suggestion is: Take more readings and plot a graph/calculate more k values (and compare). Vague reference as: Few readings. Take more readings and calculate average. Only one reading Are not credited !! this point could not have been pointed by students ..not me at least so our CIE ..grants this 2 marks FREE everytime !! but the other sources of error should be pointed by u while you are doing this experiment..and one sensible way of doing it is that u can compare it with the experiment carried out in question 1 and ..notice the major flaws in this procedure so suggest an error and the possible METHOD for its elimination..as the second part (suggesting..) usually carries four method marks with it. [20]
So 40 marks are all yours..and thank me if you liked it..because your gratitude is the fuel !!
Hari om tadsat !!
