How scienceworks -errors

Teacher’s Notes
This sequence of slides is designed to introduce, and explain,
the idea of errors in practical work, as explained on
pages 8 and 362 in New Physics for You, 2006 & 2011 editions

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How Science works:

Errors

N w Phy s ic s fo r Yo u, pages 8, 362
e

Learning Objectives

You should learn :

• About different types of errors,

• How to reduce them when you
are doing your practical work.

What is an error?
error
An…causing
an error result
…so the
is a mistakein
is not accurate.
of some results…
your kind...

What is an error?

Some are due to
human error…

For example,
by not using the
equipment correctly

Let’s look at
some examples.

Human error
Example 1
Professor Messer
is trying to
measure the length
of a piece of wood:

Discuss what he is doing wrong.
How many mistakes
can you find? Six?

Human error
Answers:
1. Measuring from 100 end
2. 95.4 is the wrong number
3. ‘mm’ is wrong unit (cm)
4. Hand-held object, wobbling
5. Gap between object & the rule
6. End of object not at the end of the rule
7. Eye is not at the end of the object (parallax)
He is on wrong side of the rule to see scale.
8.

How many did you find?

Human error
Example 2 your
eye

Reading a scale:

Discuss the best position
to put your eye.

Human error
your
2 is best. eye

1 and 3 give the
wrong readings.
This is called a
parallax error.
It is due to the gap here,
between the pointer and
the scale.
Should the gap be wide or narrow?

Anomalous results

When you are doing your practical work,
you may get an odd or inconsistent or
‘anomalous’ reading.
This may be due to a simple mistake in
reading a scale.
The best way to identify an anomalous
result is to draw a graph.
For example . . .

Anomalous results

Look at this graph: x
x
x
Which result do x

you think may be x
anomalous? x

A result like this should be taken again, to
check it.

Types of errors

When reading scales,
there are 2 main types of error:

• Random errors
• Systematic errors.

Let’s look at some examples . . .

Random errors

These may be due to
human error,
a faulty technique,
or faulty equipment.

To reduce the error,
take a lot of readings,
and then calculate the average (mean).

Systematic errors

These errors cause readings to be shifted
one way (or the other) from the true reading.

Your results will be systematically wrong.

Let’s look at some examples . . .

Systematic errors

Example 1
Suppose you are
measuring with a ruler:

If the ruler is wrongly
calibrated, or if it expands,
then all the readings will be
too low (or all too high):

Systematic errors

Example 2
If you have a parallax
error:

with your eye
always too high
then you will get a systematic error
All your readings will be too high.

Systematic errors

A particular type of systematic error

is called a zero error.

Here are some examples . . .

Zero errors

Example 3
A spring balance:

Over a period of time,
the spring may weaken,
and so the pointer
does not point to zero:

What effect does this have on all the readings?

Zero errors

Example 4
Look at this
top-pan balance:

It has a zero error.
There is nothing on it,
but it is not reading zero.

What effect do you think this will have
on all the readings?

Zero errors

Example 5
Look at this
ammeter:

If you used it like this,
what effect would it
have on your results?

Zero errors

Example 6
Look at this
voltmeter:

What is the first thing
to do?

Use a screwdriver here
to adjust the pointer.

Zero errors

Example 7
Look at this
ammeter:

What can you say?

Is it a zero error?
Or is it parallax?

Zero error, Parallax error
Example 8
Look at this ammeter:
It has a mirror
behind the pointer,
near the scale.
What is it for?
When theyou useof the pointer in the mirror
How can image it to stop parallax error?
is hidden by the pointer itself,
then you are looking at 90o, with no parallax.

In summary
• Human errors can be due to faulty technique.
• Parallax errors can be avoided.
• Anomalous results can be seen on a graph.

• Random errors can be reduced by taking
many readings, and then calculating the
average (mean).
• Systematic errors, including zero errors, will
cause all your results to be wrong.

Learning Outcomes
You should now:
• Understand the effects of
- Human error, including parallax error,
- Random errors,
- Systematic errors, including zero errors
• Be able to reduce these errors
when doing your practical work
• Be able to identify anomalous results.

For more details, see:

 New Physics for You, page 362

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How scienceworks -errors

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