A-LEVEL Physics: 3.1.1, 3.1.2, 3.1.3 (PMT) Flashcards
What are ‘SI Units’?
SI Units are the Fundamental Units.
The ‘SI Units’ are made up of: (6)
-Mass (m): Kilograms (Kg)
-Length (l): Metres (m)
-Time (t): Seconds (s)
-Amount of Substance (n): Moles (mol.)
-Temperature (t): Kelvin (K)
-Electric Current (I): Amperes (A)
The SI Units can be Derived by their…
Equation.
How can you Find the SI Units of Force (F)?
Multiply the Units of Mass & Acceleration (F=ma).
Kg * ms
The SI Units of Voltage Can be Found by a Series of Steps: (3)
- V = E/Q
where E is Energy, & Q is Charge,
E = 1/2 m v^2
so the SI Units for Energy is Kgm^2s^-2
(the Units for Speed (v) are ms^-1, so squaring these gives m^2s^-2). - Q=It (where I is Current) so the Units for Q and As (Ampere Seconds).
-So V = Kgm^2s^-2 / As
V = Kgm^2s^-3A^-1
The Prefixes which Could be Added Before Many SI Units, in Order of Smallest to Largest: (11)
-Femto (f): 10^-15
-Pico (p): 10^-12
-Nano (n): 10^-9
-Micro (µ): 10^-6
-Milli (m): 10^-3
-Centi (c): 10^-2
-Kilo (k): 10^3
-Mega (M): 10^6
-Giga (G): 10^9
-Tera (T): 10^12
___ Errors Affect Precision.
Random.
Random Errors Affect Precision. What does this Mean?
Random Errors Affect Precision, Meaning they Cause Differences in Measurements, which Causes a Spread about the Mean.
You Cannot get Rid of All ___ Errors.
Random.
What is an Example of Random Errors?
Electronic Noise.
Steps to Reduce Random Errors: (3)
-1) Take at Least 3 Repeats, & Calculate a Mean. By Averaging Out your Results, you Reduce the Negative Effect of Anomalous Results. This Method also Allows Anomalies to be Identified.
-2) Use Computers/Data Loggers/Cameras to Reduce Human Error & Enable Smaller Intervals.
-3) Use Appropriate Equipment, e.g. a Micrometer has Higher Resolution (0.1mm) than a Ruler (1mm).
What are ‘Random Errors’?
Random Errors are Errors in Measurements Caused by Factors which Vary from One Measurement to Another.
What are ‘Systematic Errors’?
Systematic Errors Affect Accuracy and Occur Due to the Apparatus or Faults in the Experimental Method. Systematic Errors Cause All Results to be either too High or too Low by the Same Amount Each Time.
What do ‘Systematic Errors’ Cause?
Systematic Errors Cause All Results to be either too High or too Low by the Same Amount Each Time.
Common Examples of Systematic Errors:
A Common Example of a Systematic Error is a Balance that isn’t Zeroed Correctly (Zero Error), or Reading a Scale at a Different Angle (this is a Parallax Error).
What is a ‘Zero Error’?
A Zero Error is when you take Measurements from a Balance that isn’t Zeroed Correctly. It is a Systematic Error.
What is a ‘Parallax Error’?
A Parallax Error is when you Read a Scale at a Different Angle. It is a Systematic Error.
To Reduce Systematic Error: (3)
-Calibrate Apparatus by Measuring a Known Value (eg Weigh 1kg on a Mass Balance). If the Reading is Inaccurate, then the Systematic Error is Easily Identified.
-In Radiation Experiments, Correct for Background Radiation by Measuring it Beforehand, and then Excluding it from the Final Result.
-Read the Meniscus (the Central Curve on the Surface of the Liquid) at Eye Level (to Reduce Parallax Error) and Use Controls in Experiments.
What does ‘Precision’ Mean?
Precise Measurements are Consistent with one another. They Fluctuate Slightly About a Mean Value. (This Doesn’t Indicate that the Value is Accurate).
What does ‘Repeatability’ Mean?
If the Original Experimenter Can Redo the Experiment with the Same Equipment & Method, then Gets the Same Results, we say that the Experiment is Repeatable.
What does ‘Reproducibility’ Mean?
If the Experiment is Redone by a Different Person, or With Different Techniques & Equipment, & the Same Results are Found, we say that the Experiment is Reproducible.
What does ‘Resolution’ Mean?
Resolution is the Smallest Change in the Quantity Being Measured that Gives a Recognisable Change in Reading.
What does ‘Accuracy’ Mean?
Accuracy is a Measurement that is Close to the True Value.
What is ‘Uncertainty’?
The Uncertainty of a Measurement is the Bounds in Which the Accurate Value is Can be Found.
e.g. 20mm+_2mm
With this Uncertainty, the True Value may be Between 18-22mm.
What is ‘Absolute Uncertainty’?
Absolute Uncertainty is Uncertainty that is Given as a Fixed Quantity.
e.g. 7+_0.6V
What is ‘Fractional Uncertainty’?
Fractional Uncertainty is Uncertainty that is Given as a Fraction of the Measurement.
e.g. 7+_ 3/35 V
What is ‘Percentage Uncertainty’?
Percentage Uncertainty is Uncertainty that is Given as a Percentage of the Measurement.
e.g. 7+_8.6%
How Can you Reduce Fractional & Percentage Uncertainty?
To Reduce Fractional & Percentage Uncertainty, you Can Measure Larger Quantities.
What is the Difference Between ‘Readings’ and ‘Measurements’?
Readings are when One Value is Found (e.g. Reading a Thermometer).
Measurements, however, are when the Difference Between 2 Readings is Found (e.g. a Ruler).
The Uncertainty in a Reading is…
+_ Half the Smallest Division (the Resolution).
e.g. for a Thermometer, the Smallest Division (the Resolution) is 1’C, so the Uncertainty is +_0.5’C.
What is the Uncertainty in a Reading?
The Uncertainty in a Reading is:
+_ Half the Smallest Division (the Resolution).
e.g. for a Thermometer, the Smallest Division (the Resolution) is 1’C, so the Uncertainty is +_0.5’C.
The Uncertainty in a Measurement is…
At Least +_1 Smallest Division (the Resolution).
e.g. a Ruler Must Include Both the Uncertainty for the Start & End Value, as Each End has +_0.5mm, they are Added, so the final Uncertainty in the Measurement is +_1mm.
What is the Uncertainty in a Measurement?
The Uncertainty in a Measurement is:
At Least +_1 Half the Smallest Division (the Resolution).
e.g. a Ruler Must Include Both the Uncertainty for the Start & End Value, as Each End has +_0.5mm, they are Added, so the final Uncertainty in the Measurement is +_1mm.
The ___ of an Instrument Affects its Uncertainty.
Resolution.
___ ___ & Given Values Will either have the ___ Quoted or Assumed to be…
Digital Readings, Uncertainty.
+_ the Last Significant Digit.
e.g. 3.2+_0.1V
For Repeated Data, the Uncertainty is…
Half the Range (Largest - Smallest Value / 2).
What is the Uncertainty for Repeated Data?
For Repeated Data, the Uncertainty is Half the Range (Largest - Smallest Value / 2).
Uncertainties Should be Given to the…
Same Number of Significant Figures as the Data.
What are Uncertainties Shown as on Graphs?
Error Bars.
Uncertainties are Shown as ___ ___ on Graphs.
Error Bars.
A Line of Best Fit on a Graph Should go Through All…
Error Bars.
How do you Calculate the Uncertainty in a Gradient?
The Uncertainty in a Gradient Can be Found by the Difference Between the Gradients of the Lines of Best & Worst Fit.
What are ‘Orders of Magnitude’?
Orders of Magnitude are Powers of Ten which Describe the Size of an Object.
Orders of Magnitude are Also Used to Compare the Sizes of Objects.
Estimation is a Required Skill. Why? What is it Needed for?
Estimation is Needed in Order to Approximate the Values of Physical Quantities, in Order to Make Comparisons, or to Check if a Value you’ve Calculated is Reasonable.
