Practical skills Flashcards
What is the uncertainty in the error bars
b) what are the key rules for error bars
c) When given Gmax and Gmin, how should you calculate G
+- 0.04m
b) line must pass through every final bar and does NOT HAVE to hit the exact top and bottom of the final bar
c) Gmax + Gmin / 2
Ways to calculate percentage uncertainty in error bars
Time for one oscillation = 15.7/10 = 1.57
For complete oscillation, bar swings from one side, goes through the vertical position, reaches the other side, and returns, meaning bar passes vertical position twice during one oscillation. Time to reach the vertical position from one side is quarter of total oscillation time:
1.57/4 = 0.3925 seconds
Determine the percentage uncertainty in the time t suggested by the precision of the recorded data. Where time for 10 oscillations = 15.7 seconds
t1 = 15.7 / 10 = 1.57 seconds
uncertainty in t1 = 0.1/10 = 0.01
percentage uncertainty = (0.01 / 1.57) x 100% = 0.64%
A ball is dropped vertically from rest, a photograph is taken every 0.045 seconds to see the ball drop, this would help calculate the value of g. Suggest why duration of the picture being taken should be as short as possible
So image is well defined and less blury
what is parallax error
apparent shift in a position when viewed from different angles, the error occurs when observers eye is not positioned directly in line with the measurement scale leading to inaccuracy
- to avoid parallax error, make sure line of sight is perpendicular to the line of sight
when asked what a student must do to obtain a value for a variable from an experiment, what should you include in your answer
- all 3 variables
- measuring instruments
- drawing graph, what goes on each axis
- how to re arrange equation to find value of the variable
Skip part a)
Calculate SI units for k
w/y = Nm^-1
Newtons is not a fundamental SI unit. State what SI units Newtons is equivalent to
Kg m s^-2
What number does this vernier scale read
2.7mm
a student is doing an experiment to determine the young modulus of a material. State what affect happens to the percentage uncertainty if diameter decreases
- in young modulus experiment, the extension is the thing being measured
- due to YM equation, smaller diameter leads to larger extensions
- reduces percentage uncertainty in extension and so in YM
- smaller diammeter means higher percentage uncertainty in cross sectional area, uncertainty in YM increases
- smaller diameter increases likelihood of material reaching limit of proportionality, percentage uncertainty in YM increases
Draw and label suitable apparatus required for measuring the Young modulus of a material in the form of a long wire.
measurements to make in Young Modulus experiment, and explain how you would take these measurments
length of wire between clamp and mark, using ruler and extension of wire
diameter of wire using micrometer
for measuring diameter, do test several time and take mean value whilst eliminating any anomalies
with a known mass
safety precaution of Young Modulus experiment
masses could fall, place sand pit underneath to catch them
goggles worn as wire is stretched tightly and could injure eyes
student is measuring how current is affected depending on where ammeter is put on at a metre ruler. Ruler has points P and Q on it.
The absolute uncertainty in identifying any minimum current is ± 0.2 cm. . He identifies Q as the position of the 8th minimum current from P. He measures the distance PQ to be 50.9 cm. Determine the percentage uncertainty in the distance PQ.
- measuring uncertainty between two points so add uncertainties
0.2 + 0.2 = 0.4
percentage uncertainty = (absolute uncertainty / reading) x 100%
= 0.4/50.9 x 100 = 0.79%
Microwaves are polarised
for stationary waves on a string experiment, how to reduce percentage uncertainty when calculating diameter of wire
- take readings at different points
- in different directions, perpendicular to the rod
- eliminate anomalous readings before calculating an average
The student uses a micrometer screw gauge to confirm his result for d.
Describe a suitable procedure that the student should carry out before using the micrometer to ensure that the measurements are not affected by systematic error
close jaws using ratchet
confirm that instrument reads zero
Absolute uncertainty = range x 0.5 = 4 x 10^-3
Mean = 0.57
Percentage uncertainty = 100% (4x10^-3 / 0.57) =0.702%
A student has a diffraction grating that is marked 3.5 × 10^3 lines per m.
(a) Calculate the percentage uncertainty in the number of lines per metre suggested by this marking.
absolute uncertainty = +- 0.1 x 10^3 m = 100 lines per metre
percerntage uncertainty = (100)/(3.5 x 10^3) x 100 = 2.86%
= 2.9%
usual absolute uncertainty in measuring two points on a ruler
each point is +- 0.5mm
as you take two points, must be multiplied by 2,
- final answer : 0.1mm
Advantages of logging for an experiment
