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  • Created by: emma
  • Created on: 09-03-15 15:56

UNCERTAINTIES

Percentage Uncertainties:

precision/value X100

0.5Xrange/value X100

Percentage difference in gradient:

Difference between actual and predicted/predicted value X100

Uncertainties in Ratios:

If multiplying, dividing, squaring etc ADD THE PERCENTAGES!

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VALIDITY

VALIDITY

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)

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EXPERIMENTAL ERROR

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

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ERRORS

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

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REDUCING UNCERTAINTIES

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.

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QUESTION 3

HOW TO ANSWER QUESTION 3:

- Detail

- 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

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PERCENTAGE DIFFERENCE

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

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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.

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