Measurements and Errors

State the SI unit for mass.

kilograms

State the SI unit for length/distance.

metres

State the SI unit for time.

seconds

State the SI unit for amount of substance.

moles

State the SI unit for temperature.

kelvins

State the SI unit for electric current.

amperes

How can SI units of any other quantity be derived?

Using their equations involving the given SI units 

What is the power of 10 for the prefix Tera?

12

What is the power of 10 for the prefix Giga?

9

What is the power of 10 for the prefix Mega?

6

What is the power of 10 for the prefix Kilo?

3

What is the power of 10 for the prefix Centi?

-2

What is the power of 10 for the prefix Milli?

-3

What is the power of 10 for the prefix Micro?

-6

What is the power of 10 for the prefix Nano?

-9

What is the power of 10 for the prefix Pico?

-12

What is the power of 10 for the prefix Femto?

-15

How many joules are in one electron volt?

1.6×10^-19

How many joules are in one kilowatt hour?

3.6×10⁶

What is a random error?

Unpredictable variation between measurements that causes a spread of values around the true value

What can be effected by random errors?

The precision of the data

How can random errors be reduced?

Take repeats and calculate a mean

Use equipment that reduces human error in readings, and that has an appropriate resolution

What is a systematic error?

An error that causes data to be away from the true value by the same amount each time due to equipment or experimental method

State and explain 2 examples of systematic error.

Zero error - when the equipment is not set to 0 before taking a reading

Parallax error - when the scale is read at the wrong angle 

How can systematic error be reduced?

Calibrate apparatus by measuring a known amount - systematic error can be identified

Measure and remove background radiation from the values in radiation experiments

Read the meniscus at eye level for liquids

What is effected by systematic error?

The accuracy of the results

What is precision?

Consistent measurements that vary only very slightly from the mean 

What is repeatability?

The ability for the original experimenter to repeat the experiment with the same method and equipment to obtain the same results

What is reproducibility?

If the experiment is redone by a different person or with different methods and equipment, to get the same result 

What is resolution?

The smallest change in a measured quantity that gives a recognisable change in reading 

What is accuracy?

The closeness of a measurement to the true value

What is uncertainty?

The bounds of a measurement in which the accurate value is expected to lie

State and explain the 3 types of uncertainty.

Absolute uncertainty - given as a fixed quantity

Fractional uncertainty - given as a fraction of the measurement

Percentage uncertainty - given as a percentage of the measurement

How can percentage or fractional uncertainty be reduced? 

Measure larger quantities

How is % uncertainty calculated?

uncertainty / value x 100 

What is the difference between a reading and a measurement?

Readings are when one value is found

Measurements are when the difference between 2 readings is found 

How is the uncertainty calculated for a reading?

± half of the smallest division

How is the uncertainty calculated for a measurement?

± at least 1 smallest division

What is the uncertainty of a digital reading?

± the last significant figure

What property of a instrument effects its uncertainty?

The resolution

How is uncertainty for repeated data?

mean ± range/2

How can the uncertainty of a ruler measurement be decreased?

Fix one end so only the uncertainty of one reading is included

How many significant figures should uncertainty be given to?

The same as the data 

How should uncertainties be combined when adding/subtracting data?

Add absolute uncertainties

How should uncertainties be combined when multiplying/dividing data?

Add percentage uncertainties

How should uncertainties be combined when raising the data to a power?

Multiply the percentage uncertainty by the power

How are uncertainties shown on graphs?

As error bars

How are a line of best fit and error bars connected?

The line of best fit should go through all errors bars (excluding anomalies)

How is uncertainty found for a gradient of a graph?

Draw a line of best fit and a line of worst fit

% uncertainty = (best-worst)/best x 100 

How is uncertainty found for the y-intercept of a graph?

Find the y-intercept for the best and worst fit lines

% uncertainty = (best-worst)/best x 100 

What are orders of magnitude?

Powers of 10 that describe the size of a value

Why is estimation important?

It is used to approximate values so they can be compared