Percentage difference in gradient:
Difference between actual and predicted/predicted value X100
Uncertainties in Ratios:
If multiplying, dividing, squaring etc ADD THE PERCENTAGES!
of Gradient: 1. Anomalous values?
2. Do the points lie close to the line of best fit?
of Experiment: 1. High % uncertainties
2. Random Errors causing high % uncertainties/ differences
3. Possible unexplained systematic error
4. Experiment not including extraneous forces (i.e friction)
SOURCES OF EXPERIMENTAL ERROR=
- Poorely drawn line of best fit
- Inaccurate extrapolation of y-intercept
- Systematic Error/ Zero Error on ________ (i.e ammeter, voltmeter...)
RELIABILITY OF RESULTS =
*CLOSENESS of repeat readings
*CLOSENESS of points to line of best fit
TYPES OF ERROR:
RANDOM: caused by unknown and unpredictable changes in the experiment; cannot eliminate these errors.
SYSTEMATIC: caused by apparatus or experimental method. These normally shift all results up or down by the same amount
WAYS OF REDUCING UNCERTAINTIES:
- Use higher precision apparatus/ higher sensitivity: reduces random errors
- CALIBRATION: Measure a known value; reduces systematic errors
- REPEATING MEASUREMENTS: take several readings and average. Reduces random errors. The more repeats, the less error.
HOW TO ANSWER QUESTION 3:
- Specify no. of readings/number of repeats
- Suggest graph AND state what to plot
- State WHAT to measure and WHICH INSTRUMENT to use and HOW to use it
- Take 3 repeat readings and average them
You may be asked to calculate the % difference between 2 or more readings and to check if the readings fall inside reasonable experimental error.
% difference =
(difference between the readings)/average of all the readings
FORCES IN EQUILIBRIUM
If an object is in equilibrium, all the forces acting on it are balanced and cancel eachother out. There are no resultant forces acting.
Hooke's Law: Extension is directly proportional to the force applied. Spring constant: K = gradient
DIRECTLY PROPORTIONAL: line must go through origin. Y=mX
PARALLAX: the position of an object appears to differ when viewed from different positions. This can cause (systematic) error.