Module 2 Flashcards
Find standard form for: Pico
10^-12
Find standard form for: Nano
10^-9
Find standard form for: Micro
10^-6
Find standard form for: Milli
10^-3
Find standard form for: Centi
10^-2
Find standard form for: Deci
10^-1
Find standard form for: Kilo
10^3
Find standard form for: Mega
10^6
Find standard form for: Giga
10^9
Find standard form for: Tera
10^12
What is the SI unit for: Luminous Intensity
Candela (cd)
What is the SI unit for: Amount of substance
Mole (mol)
What does it mean for an equation to be homogeneous?
It means that all the terms in the equation have the same units.
Use units to show that the equation v = u + at is homogeneous.
v and u are both velocities, with base units ms^-1
at is acceleration x time, so ms^-2 X s = ms^-1
The units of all three terms in the equaton are ms^-1, so the equation is homogeneous.
What is an error?
The difference between a measured value and the true or theoretically correct one.
What is a random error?
Unpredictable variation between measurements that leads to a spread of values about the true value. (above and below the true value)
How can random error be reduced?
By taking repeat measurements.
What do systematic errors cause?
Causes all readings to differ from the true value by a fixed amount.
It tends to shift all measurements in the same direction.
Could repeat readings be used to reduce systematic error?
No. Systematic error cannot be corrected by repeat readings, instead a different technique or apparatus should be used.
What is a zero error?
What does it result in?
A form of systematic error, caused when a measuring instrument is not properly calibrated or adjusted, giving a non-zero value when the true value is zero.
This results in all measurements being offset by a fixed amount.
What is a parallax error?
An error caused by reading a scale at the wrong angle.
Give an example of a parallax error.
When your eye is not parallel with the meniscus when using a measuring cylinder.
Give an example of a random error.
Variable heating in circuits causing variations in the current being measured.
OR
An unexpectedly large extension of a metal wire, due to a fault in its structure.
What is a systematic error?
An error introduced by an inaccuracy in the apparatus or its use by the person conducting the investigation.
Give an example of a systematic error.
The scale printed on a metre ruler is incorrect and the ruler scale is only 99.0cm long.
Define precision.
A measure of how close a measurement is to the mean value. It only gives an indication of the magnitude or random errors, not how close data is to the true value.
The smaller the spread of values, the higher the precision.
Define accuracy.
A measure of how close a measurement is to the true value.
What combinations of precision and accuracy can you have?
A value can have poor accuracy and poor precision.
A value can have poor accuracy but good precision.
A value can have good accuracy and good precision.
How do systematic errors affect precision and accuracy?
Accuracy is affected by any systematic errors that are not accounted for, as the systematic error takes the measured value away from its true value.
Precision, which is ultimately determined by the resolution of the apparatus being used, remains unaffected.
What is the absolute uncertainty of a measurement?
It shows how large the uncertainty actually is, and has the same units as the quantity being measured.
What is percentage uncertainty?
The absolute uncertainty divided by the measured value, expressed as a percentage.
The diameter of a ball is 63mm.
A metre ruler with centimetre and millimetre graduations was used.
What is the absolute uncertainty?
+- 0.5mm
So the diameter of the ball could be expressed as 63 +- 0.5mm
How do you determine the uncertainty involving the use of a stopwatch (precise to 0.01s)?
Use the uncertainty of reaction time (about 0.5s) when stating a time value and its absolute uncertainty.
This is done because human reaction times are not as quick as 0.01s.
