Product survey

25th February 2000 at 00:00
What kind of thermometer do you need? Gerald Haigh offers a degree of choice.

You can make a thermometer out of any substance or material just so long as it visibly changes as temperature goes up and down. Your own body gives good indications of hot and cold weather, for example. In fact, this sort of observation is an appropriate way of introducing temperature measurement to children, rather than leaping straight into talking about degrees and thermometers.

Our old friend the liquid-filled thermometer - reputedly invented by Galileo - simply makes use of one of these visible changes in that the liquid expands and contracts up and down a very narrow tube (the capillary) as the temperature rises or falls. Liquid thermometers are accurate and simple. They cover most of the temperature range that we generally need to measure in school, and it is easy for children to see how they work.

The best liquid to use is mercury because it is accurate and it stays liquid over a wide range. Mercury thermometers used to be common in schools and pupils welcomed the breakages that gave them lovely little silver globules to play with. They are used much less in school now and are banned by some authorities because mercury is a brain poison.

Today's educational liquid thermometers are filled with a spirit akin to alcohol. This also poisons the brain, but the amount contained in a thermometer would make a miserably weak martini. There are other kinds of thermometer. One type uses the varying electrical resistance with temperature of some materials. In this case the temperature is shown on a digital display. Another uses a bi-metallic strip to drive a pointer across a dial. Yet another makes use of the fact that a film of liquid crystals can be made to turn transparent at different temperatures.

Primary teachers use thermometers to study the weather and aspects of the human body. The measurement of temperature is specifically mentioned in the science section of the new key stage 2 national curriculum.

At secondary school, thermometers are widely used in science departments, for example for measuring temperature in chemical changes, monitoring the temperature in some biological experiments, and for physics investigations involving cooling curves. In fact, the rate of breakage by pupils of small thermometers has traditionally been a major expense in a secondary science department. Well-organised teachers will make thermo-meters last, but some breakages are almost inevitable - and a broken glass thermometer is dangerous. There is always an interest in those designed to last.

I looked at a typical range of school thermometers. All were accurate enough for their purpose. They were supplied by Technology Teaching Systems but they, or similar instruments, are available from other suppliers and prices should be compared. (All prices are excluding VAT).

Wall Thermometer. pound;5.45. This is a very familiar object - a 40cm thermometer to hang on the wall. They used to have a wooden case, but plastic is now used. Many schools will have one in each room, as much for health and safety reasons as for use by pupils. It has both Fahrenheit and Celsius scales, which many science advisers and teachers will frown upon as confusing.

Giant Wall Thermometer. pound;19.75. Try to buy this one rather than the standard wall thermometer. It is bigger (64cm), is strongly made of aluminium and has much greater educational use. The whole class can see it, for example.

In particular there are two scales, one each side of the capillary. These can be removed as long paper strips, so children can record temperatures directly on the scale and then remove the strip of paper. Mount these strips side by side to make a graph of the daily temperature - a striking way of teaching data-gathering and display.

Infant Thermometer. pound;6.75. Also a wall thermometer, this has easy-to-read numbers and scale markings from 0 to 35 C. Graphics relate the temperature scale to the words "hot", "warm" and "cold" as they apply to a classroom. It can be held up in front of the class and its design will sit easily with a key stage 1 wall display.

Breaksafe Thermometer. pound;4.50. This is an advanced form of the traditional classroom glass thermometer. The glass tubing is encased in plastic, which not only makes it durable but holds the glass together if it breaks.

A piece of plastic on the bottom protects the bulb if it is tapped on the bench or on the base of a container. At the top, another piece of plastic will act as a hook or a hand-hold and will stop it rolling along the table.

It comes in a square section plastic case, which makes it easy and safe to stack in a cupboard or lie on a shelf . An excellent piece of equipment for key stage 2 upwards.

Descriptive Thermometer. pound;12.50 for a pack of five. The disadvantage of small liquid thermometers is the difficulty of reading them. Younger primary children will inevitably struggle.

So, with words instead of numbers, this simple liquid crystal display (LCD) thermometer for key stage 1 has five panels relating temperature to the child's body heat - "colder", "cooler", "me", "warmer", "hotter".

The appropriate panel changes colour in response to the temperature. It has a big closed circular hook at one end. This is a good, cheap and cheerful resource that could be hung in all sorts of places.

There are clear links to language and vocabulary, and a good teacher will use it in contexts other than science.

Numeric Thermometer. pound;12.50 pack of five. Working on the same principle as the descriptive thermometer, this has numbers instead of words. The 10 panels show the temperature in five-degree steps from - 5 to 40C.

Suitable for upper key stage 1 and key stage 2, this is also cheap and can be used for a range of investigations and discussions. Occasionally two adjacent panels show up, but this apparent disadvantage can be a teaching point.

Forehead Thermometer. pound;8.50 pack of five. Taking body temperature in class can be difficult. The most practical way is to use one of these. It uses the same "colour change" LCD principle as the numeric and descriptive thermometers, but comes as a small flexible strip with a scale from 35 to 40C that you press against the forehead.

You could use this for classroom investigations - testing whether exercise raises body temperature, for example.

Stirring Thermometer. pound;3.40. Another "protected" glass thermometer for classroom use. It comes in a transparent plastic case which has holes so that you could use it without taking it out - although that makes it marginally more difficult to read.

If you take it out, a good chunky plastic holder at one end prevents rolling. The whole assembly, when in the case, has a fountain pen-type pocket clip, which also serves well as a "roll protector".

Electronic Stem Thermometer. pound;14.80. This is effectively a metal stick with a plastic handle. The temperature is measured at the tip and displayed on a digital readout in the handle.

The "stick" is vulnerable, and protected when not in use by a plastic sleeve. It works well, and has the advantage of a "hold" button so you can keep the measured temperature on display after you have withdrawn the probe. You could use this in a kitchen or food technology department, for example, to make sure food was being cooked, or refrigerated, at a safe temperature - it reads from - 50 to 150C.

Technology Teaching Systems, Unit Seven, Monk Road, Alfreton, Derbyshire DE55 7RL. Free phone 0800 318686 Free fax 0800 137525. e-mail suppliers are:Philip Harris Education:01543 480077Griffin and George: 01509 233344Hope Education: 0161 3662900Novara plc: 0115 936 0210A list of educational suppliers, which can be searched by curriculum area, is available from British Educational Suppliers Association (BESA) at: School Science Service, to which all local authorities subscribe, has a free, detailed publication for primary schools, Measuring Temperature. This lists all types of thermometer and makes useful comparisons. CLEAPSS School Science Service, Brunel University, Uxbridge UB8 3PH. Tel: 01895 251496 fax: 01895 814372


There are no duds here. TTS has great credibility, especially with secondary science and technology teachers, and products are carefully chosen. However, these are the ones I liked best: Giant Wall Thermometer: Top marks to the manufacturer for being aware of the need for whole-class resources in the primary classroom. Value for money even at this price.

Descriptive Thermometer: If you are looking for cheapness and efficiency at key stage 1, this is probably the best of the bunch.

Breaksafe Thermometer: Top marks for a classroom thermometer at key stage 2 upwards. Dearer than some basic thermometers, but survives better and should be economical in the long run.

Stirring Thermometer: Runner-up in the same category for the same reasons.

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