A-LEVEL Physics: 3.1.1, 3.1.2, 3.1.3 (PMT)

Question 1

What are ‘SI Units’?

Answer 1

SI Units are the Fundamental Units.

Question 2

The ‘SI Units’ are made up of: (6)

Answer 2

-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)

Question 3

The SI Units can be Derived by their…

Answer 3

Equation.

Question 4

How can you Find the SI Units of Force (F)?

Answer 4

Multiply the Units of Mass & Acceleration (F=ma).

Kg * ms

Question 5

The SI Units of Voltage Can be Found by a Series of Steps: (3)

Answer 5

• 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

Question 6

The Prefixes which Could be Added Before Many SI Units, in Order of Smallest to Largest: (11)

Answer 6

-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

Question 7

___ Errors Affect Precision.

Answer 7

Random.

Question 8

Random Errors Affect Precision. What does this Mean?

Answer 8

Random Errors Affect Precision, Meaning they Cause Differences in Measurements, which Causes a Spread about the Mean.

Question 9

You Cannot get Rid of All ___ Errors.

Answer 9

Random.

Question 10

What is an Example of Random Errors?

Answer 10

Electronic Noise.

Question 11

Steps to Reduce Random Errors: (3)

Answer 11

-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).

Question 12

What are ‘Random Errors’?

Answer 12

Random Errors are Errors in Measurements Caused by Factors which Vary from One Measurement to Another.

Question 13

What are ‘Systematic Errors’?

Answer 13

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.

Question 14

What do ‘Systematic Errors’ Cause?

Answer 14

Systematic Errors Cause All Results to be either too High or too Low by the Same Amount Each Time.

Question 15

Common Examples of Systematic Errors:

Answer 15

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).

Question 16

What is a ‘Zero Error’?

Answer 16

A Zero Error is when you take Measurements from a Balance that isn’t Zeroed Correctly. It is a Systematic Error.

Question 17

What is a ‘Parallax Error’?

Answer 17

A Parallax Error is when you Read a Scale at a Different Angle. It is a Systematic Error.

Question 18

To Reduce Systematic Error: (3)

Answer 18

-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.

Question 19

What does ‘Precision’ Mean?

Answer 19

Precise Measurements are Consistent with one another. They Fluctuate Slightly About a Mean Value. (This Doesn’t Indicate that the Value is Accurate).

Question 20

What does ‘Repeatability’ Mean?

Answer 20

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.

Question 21

What does ‘Reproducibility’ Mean?

Answer 21

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.

Question 22

What does ‘Resolution’ Mean?

Answer 22

Resolution is the Smallest Change in the Quantity Being Measured that Gives a Recognisable Change in Reading.

Question 23

What does ‘Accuracy’ Mean?

Answer 23

Accuracy is a Measurement that is Close to the True Value.

Question 24

What is ‘Uncertainty’?

Answer 24

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.

Question 25

What is ‘Absolute Uncertainty’?

Answer 25

Absolute Uncertainty is Uncertainty that is Given as a Fixed Quantity.
e.g. 7+_0.6V

Question 26

What is ‘Fractional Uncertainty’?

Answer 26

Fractional Uncertainty is Uncertainty that is Given as a Fraction of the Measurement.
e.g. 7+_ 3/35 V

Question 27

What is ‘Percentage Uncertainty’?

Answer 27

Percentage Uncertainty is Uncertainty that is Given as a Percentage of the Measurement.
e.g. 7+_8.6%

Question 28

How Can you Reduce Fractional & Percentage Uncertainty?

Answer 28

To Reduce Fractional & Percentage Uncertainty, you Can Measure Larger Quantities.

Question 29

What is the Difference Between ‘Readings’ and ‘Measurements’?

Answer 29

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).

Question 30

The Uncertainty in a Reading is…

Answer 30

+_ 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.

Question 31

What is the Uncertainty in a Reading?

Answer 31

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.

Question 32

The Uncertainty in a Measurement is…

Answer 32

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.

Question 33

What is the Uncertainty in a Measurement?

Answer 33

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.

Question 34

The ___ of an Instrument Affects its Uncertainty.

Answer 34

Resolution.

Question 35

___ ___ & Given Values Will either have the ___ Quoted or Assumed to be…

Answer 35

Digital Readings, Uncertainty.
+_ the Last Significant Digit.
e.g. 3.2+_0.1V

Question 36

For Repeated Data, the Uncertainty is…

Answer 36

Half the Range (Largest - Smallest Value / 2).

Question 37

What is the Uncertainty for Repeated Data?

Answer 37

For Repeated Data, the Uncertainty is Half the Range (Largest - Smallest Value / 2).

Question 38

Uncertainties Should be Given to the…

Answer 38

Same Number of Significant Figures as the Data.

Question 39

What are Uncertainties Shown as on Graphs?

Answer 39

Error Bars.

Question 40

Uncertainties are Shown as ___ ___ on Graphs.

Answer 40

Error Bars.

Question 41

A Line of Best Fit on a Graph Should go Through All…

Answer 41

Error Bars.

Question 42

How do you Calculate the Uncertainty in a Gradient?

Answer 42

The Uncertainty in a Gradient Can be Found by the Difference Between the Gradients of the Lines of Best & Worst Fit.

Question 43

What are ‘Orders of Magnitude’?

Answer 43

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.

Question 44

Estimation is a Required Skill. Why? What is it Needed for?

Answer 44

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.