# Measure Accurately

In this worksheet, students will study a variety of scientific equipment and learn how to use each piece accurately, as well as how to handle experimental data.

Key stage:  KS 3

Curriculum topic:   Working Scientifically

Curriculum subtopic:   Measurement

Difficulty level:

### QUESTION 1 of 10

If you are shooting an arrow at a target, is it better to be accurate or consistent?

Surely as an archer, you want to be accurate, right? You want to hit that bulls’ eye!

Some people would rather the archer hit the same place each time at least that way she or he is reliable.

Scientific investigation is similar, only with equipment, not deadly arrows.

Do you go for equipment that will inform you of the accurate results or do you go for equipment that will give you a small grouping of answers? This is what we will be looking at in this worksheet.

There is a variety of scientific equipment and apparatus for each scientific experiment. Each needs to used properly so that the measurements taken are accurate. You will be presented with a variety of situations related to using scientific apparatus and handling data.

It is essential that scientific data are both accurate and precise:

Accuracy is how close to the true value of a quantity the measurement is.

Precision is the degree to which the results recorded will be the same if the experiment is to be reproduced under the exact same conditions.

Now it's over to you. Turn back to the introduction whenever you need.

A group of pupils perform an experiment twice under the same conditions. Their results are slightly higher the second time.

Is the statement below true or false?

"The experiment is not very precise."

True

False

Complete the sentence below.

A pupil has measured the volume of water in a measuring cylinder to be 10 ml. The volume is actually 11 ml. The pupil's results are not __________.

Accurate

Precise

Repeatable

A pupil has made a miniature parachute and tests it to see how long it will take it to reach the ground.

He repeats the experiment five times and the measurements recorded are as follows:

 1 20 s 2 20.1 s 3 21 s 4 20.5 s 5 19.9 s

There is variation in his measurements. What is the range of his measurements?

Clue: in order to find the range, you need to identify the lowest and highest measurement. It will also help to put the readings in order from low to high.

19.9 to 20 s

20 to 21 s

19.9 to 21 s

Have another look at the results table below.

 1 20 s 2 20.1 s 3 21 s 4 20.5 s 5 19.9 s

Now calculate the mean (average) of the readings.

Clue: in order to calculate the mean, you need to add all readings, then divide by how many readings there are.

23 s

20.3 s

101.5 s

A pupil needs to measure water temperature in a bath. She has two thermometers to choose from: a toy thermometer and a scientific laboratory thermometer.

Which one will be more accurate?

The toy thermometer

The scientific thermometer

A pupil has to compare the distances two toy cars travel on a ramp.

He has two rulers: one with a millimetre scale and one with centimetres only.

Which one do you suggest the pupil uses?

Millimetre

Centimetre

The meniscus is formed because different liquids react differently to surface tension.

The diagram below shows the meniscus formed by water and mercury.

How can you correctly measure the volume of the liquid?

The highest point of the meniscus must be measured

The lowest point of the meniscus must be measured

The meniscus must be measured at eye level of the centre of the meniscus

A pupil wants to measure the rate of photosynthesis in pond water in a large beaker of water. This can only be done by identifying and counting the bubbles of oxygen.

The pupil wonders what she could do in order to increase the accuracy of her counting.

Choose the most appropriate solution.

She can't do the experiment accurately unless she finds a special instrument that can count the bubbles for her

She can ask some of her classmates to count with her: the more people counting, the more chances that they will identify the correct number of bubbles

This is an impossible task and this experiment should not be carried out

What does reliable data refer to?

Accurate data

Reproducible results

Valid results

A pupil was asked to measure the rate of reaction of hydrochloric acid and magnesium. She investigates the rate of reaction between sulfuric acid and calcium carbonate.

Why are her results not valid even though they are accurate?

The results are precise, therefore they are valid

The results are accurate, but not relevant

The results can be reproduced easily

• Question 1

A group of pupils perform an experiment twice under the same conditions. Their results are slightly higher the second time.

Is the statement below true or false?

"The experiment is not very precise."

True
EDDIE SAYS
The statement is true. For increased precision, the results should be the same. However, it's also possible that measurements were not accurate which also impacts precision.
• Question 2

Complete the sentence below.

A pupil has measured the volume of water in a measuring cylinder to be 10 ml. The volume is actually 11 ml. The pupil's results are not __________.

Accurate
EDDIE SAYS
The pupil's results are not accurate, because the measurement is 1 ml lower than the actual quantity. How are you getting on?
• Question 3

A pupil has made a miniature parachute and tests it to see how long it will take it to reach the ground.

He repeats the experiment five times and the measurements recorded are as follows:

 1 20 s 2 20.1 s 3 21 s 4 20.5 s 5 19.9 s

There is variation in his measurements. What is the range of his measurements?

Clue: in order to find the range, you need to identify the lowest and highest measurement. It will also help to put the readings in order from low to high.

19.9 to 21 s
EDDIE SAYS
Range = the measure between the lowest and highest measurement. This means that the range here is 19.9 s to 21 s.
• Question 4

Have another look at the results table below.

 1 20 s 2 20.1 s 3 21 s 4 20.5 s 5 19.9 s

Now calculate the mean (average) of the readings.

Clue: in order to calculate the mean, you need to add all readings, then divide by how many readings there are.

20.3 s
EDDIE SAYS
The mean is worked out by adding together all of the values. Then, pressing '=' on your calculator and then dividing it by the number of items you added together. Mean = (20 + 20.1 + 21 + 20.5 + 19.9) / 5 = 20.3 s. Why not make revision flashcards so that you remember the calculation required?
• Question 5

A pupil needs to measure water temperature in a bath. She has two thermometers to choose from: a toy thermometer and a scientific laboratory thermometer.

Which one will be more accurate?

The scientific thermometer
EDDIE SAYS
This one was easy! The pupil will have more accurate results if she uses the scientific thermometer. More expensive equipment is more sensitive, and thus more accurate, as it can detect small changes in temperature. Great focus, you're halfway.
• Question 6

A pupil has to compare the distances two toy cars travel on a ramp.

He has two rulers: one with a millimetre scale and one with centimetres only.

Which one do you suggest the pupil uses?

Millimetre
EDDIE SAYS
The ruler with a millimetre scale will give a more precise measurement, as it can measure right down to the closest millimetre. Hopefully, this is becoming less daunting and you are able to differentiate between precision and accuracy!
• Question 7

The meniscus is formed because different liquids react differently to surface tension.

The diagram below shows the meniscus formed by water and mercury.

How can you correctly measure the volume of the liquid?

The meniscus must be measured at eye level of the centre of the meniscus
EDDIE SAYS
The volume of liquid can be measured at eye level of the centre of the meniscus, as shown in the image below.

• Question 8

A pupil wants to measure the rate of photosynthesis in pond water in a large beaker of water. This can only be done by identifying and counting the bubbles of oxygen.

The pupil wonders what she could do in order to increase the accuracy of her counting.

Choose the most appropriate solution.

She can ask some of her classmates to count with her: the more people counting, the more chances that they will identify the correct number of bubbles
EDDIE SAYS
The pupil could ask some of her classmates to count with her. The more people counting, the more chances that they will identify the correct number of bubbles. Sometimes more people working together can produce more accurate results!
• Question 9

What does reliable data refer to?

Reproducible results
EDDIE SAYS
Reliable results are results that can be reproduced, if done under the same conditions, by you and others. You're making great progress!
• Question 10

A pupil was asked to measure the rate of reaction of hydrochloric acid and magnesium. She investigates the rate of reaction between sulfuric acid and calcium carbonate.

Why are her results not valid even though they are accurate?

The results are accurate, but not relevant
EDDIE SAYS
The results are accurate, but not relevant. In order for results to be valid, they must be both reliable and relevant. Great focus, that's another activity ticked off!
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