25.3 - Recording Results in a Table

What a table question looks like

Tables appear in two different places on the Cambridge practical paper.

In the experiment questions (printed table)

• The table is usually already printed for you to fill in.
• Sometimes headings are given and you supply the values; sometimes values are given and you complete the missing headings.
• Heading marks are for writing each heading as a quantity together with its unit (e.g. l / cm).

In the planning question (draw your own table)

• You draw the table from scratch as one of the planning marks.
• Do not enter any numbers - The experiment has not been carried out.
• The mark is for the structure: the correct columns for your method, correctly headed with units.

Three key rules for tables

1. A column for every quantity you measure or calculate.
2. Each heading written as the quantity and its unit (e.g. l / cm).
3. Raw values in a column all recorded to the same number of decimal places.

A typical question

draw a table, or tables, with column headings, to show how you would display your readings (you are not required to enter any readings in the table)

Building the table

Take an experiment measuring how the resistance of a wire depends on its length. At each length, you record the potential difference $V$ and current $I$, then calculate resistance from $R=\frac{V}{I}$.

Which columns to include

• One column for every quantity measured or calculated. Put the independent variable first, then the raw readings, then calculated values.
• For this experiment, that requires four columns: length, potential difference, current, and resistance.
• If you calculate resistance without recording the raw $V$ and $I$ readings, the examiner cannot award marks for your measurements.

How to write column headings

Headings are written as quantity / unit:

• Either the full name or the recognised symbol is accepted (e.g. length / cm or l / cm).
• Units belong in the heading, not next to each value. Writing units inside the table cells loses the mark.
• If a quantity has no unit (such as a ratio of two lengths), write only the quantity name or symbol.

Keeping values consistent

• Every raw value in a column must be recorded to the same number of decimal places, determined by the precision of the measuring instrument.
• For example, lengths measured with a millimetre rule are recorded to one decimal place in centimetres (e.g. 20.0, not 20).
• Ammeter readings to the nearest 0.01 A are all recorded to two decimal places.

Drawing a table for the planning question

For a plan investigating how lid thickness affects the rate of cooling of hot water:

• Ruled columns, each headed with a quantity and unit, with empty rows and no data entered.
• Every quantity mentioned in your method must have a column in the table with its correct unit.

Common exam questions

Question 1

How should a column heading for a length measured in centimetres be written?

As length / cm or l / cm - the quantity, then a solidus, then the unit. Either the name or the recognised symbol for the quantity is accepted.

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Question 2

A student writes the unit after every value in the body of the table. Why does this lose the mark?

Because the mark is for the unit appearing in the heading. The heading states the unit once for the whole column, which is why the values themselves are written as bare numbers.

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Question 3

A column of lengths reads 20.0, 40.0, 60, 80.0. What is wrong?

The third value is given to a different precision from the rest. If the rule was read to the nearest millimetre it should be 60.0, and every value in a column should be to the same number of decimal places.

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Question 4

A student measures the potential difference and the current, then calculates the resistance. How many columns should the table have, and why?

Three at least, one for each of the two readings and one for the calculated resistance, plus a column for whatever quantity was being changed. Every quantity measured or calculated gets a column so that the working is visible.

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Question 5

The plan question says you are not required to enter any readings. What is the table mark actually for?

For the structure: the correct columns for the independent variable, the dependent variable, and anything else the method measures, each headed with a quantity and a unit.

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Question 6

A student's plan describes timing how long water takes to cool, but her table has only one column, headed "results". What is missing?

Columns for each quantity she said she would measure, each with a heading and a unit - the thickness or other independent variable, the temperature in °C, and the time in s.

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Question 7

A column holds the ratio of two lengths. What should the heading be?

Just the quantity, with no unit, because dividing one length by another leaves a number with no units at all.