Practicals paper 3 - A level Physics Edexcel
What is the objective of core practical 1 'determine the acceleration of a freely-falling object'?
To measure the acceleration due to gravity g of an object falling freely and consider the alternative methods: a) object falling through a trap doo...
What is the objective of core practical 1 'determine the acceleration of a freely-
falling object'?
To measure the acceleration due to gravity g of an object falling freely and consider the
alternative methods: a) object falling through a trap door and b) object falling through a
light gate
What is the safety for the 'determine the acceleration of a freely-falling object'
practical?
Ensure that any apparatus that might topple over is secure
Be aware of falling objects
For method B, turn off electromagnet when not in use
How do you work out the percentage uncertainty?
(uncertainty/mean value) x 100%
How do you calculate the percentage difference?
((experiment result - accepted value)/ accepted value) x 100%
What equipment do you need method A in the 'determine the acceleration of a
freely-falling object' practical?
Metre ruler or tape with millimetre resolution
Steel sphere
Electronic timer
Electromagnet to retain steel sphere
Trap door
What equipment do you need method B in the 'determine the acceleration of a
freely-falling object' practical?
Metre ruler or tape with millimetre resolution
Falling object, such as a 2cm dowel, 10cm long
Means to guide the dowel through the light gate
Light gate and datalogger
,What is method A for the 'determine the acceleration of a freely-falling object'
practical?
1) Drop the object from rest and record the time taken t for the sphere to fall to the trap
door
2) Repeat the measurement for the sphere to fall to the trap door twice more and work
out the mean value.
3) Measure and record the height h fallen by the sphere.
4) Repeat the timing of the drop as you vary the height; you should take at least 6
readings
5) Use half the range in your readings for t as the uncertainty in t. Calculate the
percentage uncertainty in t.
What is method B for the 'determine the acceleration of a freely-falling object'
practical?
1) Drop the object from rest and record the time taken t for the dowel to pass through
the light gate
2) Repeat the measurement for the dowel to pass through the light gate twice more and
work out the mean value.
3) Measure and record the height h fallen by the sphere.
4) Repeat the timing of the drop as you vary the height; you should take at least 6
readings
5) Use half the range in your readings for t as the uncertainty in t. Calculate the
percentage uncertainty in t.
6) Measure the length of the dowel.
How do you analyse the results of method A in the 'determine the acceleration of
a freely-falling object' practical?
t^2 (y axis) against h (x axis) and work out the gradient m of the line of best fit. Calculate
a value for g where g=2/m.
How do you analyse the results of method B in the 'determine the acceleration of
a freely-falling object' practical?
,Use your value for the length of the dowel to calculate the mean speed v of the dowel
as it passes through the light gate. Plot a graph of v^2 against h and work out the
gradient m of the line of best fit. Calculate a value of g where g=m/2.
How do you do the percentage uncertainty for method A of the 'determine the
acceleration of a freely-falling object' practical?
The percentage uncertainty in t^2 is twice that in t. Use this to draw on your plot's error
bars - in the y direction only. You can use a typical mid-range value for calculating
uncertainties and need not work out a separate error bar for each value. Draw further
lines of fit to calculate the percentage uncertainty in your value for g.
How do you do the percentage difference in the 'determine the acceleration of a
freely-falling object' practical?
Calculate the percentage difference between your value and the accepted value of
9.81ms^-2 and comment on the accuracy of your method.
What is important to remember when drawing the graph for the 'determine the
acceleration of a freely-falling object' practical?
Ensure the points plotted on a graph take up more than half of the available space on
both scales. You do not always need an origin on a graph.
Keep scales simple, one big square as 5,10 or 20 is ideal. One big square as 3 or 7 is
very difficult to plot on and often leads to errors.
Always consider whether or not the graph line should go through the origin. Straight
lines should be drawn with the aid of a ruler - one long enough to cover the full length of
the line.
How is SUVAT related to method A of the 'determine the acceleration of a freely-
falling object' practical?
s=ut+1/2at^2 where u=0,a=g,s=h
t^2=2h/g and comparison with y=mx+c shows that plotting t^2 against h should be a
straight line passing through the origin with gradient 2/g
How is SUVAT related to method B of the 'determine the acceleration of a freely-
falling object' practical?
, v^2=u^2+2as where u=0, a=g, s=h
v^2=2gh and comparison with y=mx+c shows that plotting v^2 against h should be a
straight line passing through the origin with gradient 2g.
Describe any advantage using light gates in the 'determine the acceleration of a
freely-falling object' practical
There should be less uncertainty in the measurement of time
Discuss the affect of air resistance on the value of g in the 'determine the
acceleration of a freely-falling object' practical?
g will have been reduced by air resistance
Explain why graph in the 'determine the acceleration of a freely-falling object'
practical should be a straight a line
A straight line has a constant gradient. The line should be straight because the gradient
depends only on g, which is constant.
What is the objective of core practical 2 'determine the electrical resistivity of a
material' practical?
To use a metal wire to determine the resistivity of a metal
What is the safety for the 'determine the electrical resistivity of a material'
practical?
Voltages and currents are small and so present no specific hazard
Disconnect wire between readings as it may get hot
Normal laboratory safety procedures should be followed
What is the equipment for the 'determine the electrical resistivity of a material'
practical?
1.05m of 34swg constantan wire
metre ruler
2 leads, one with a crocodile clip on one end
digital multimeter switched to the lowest ohms scale with both the leads plugged in
micrometer screw gauge
What is the method for the 'determine the electrical resistivity of a material'
practical?
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