OCR a Level Physics B Lesson Element -Inverse Square Law in Electrostatics

Learner Resource 1, Thermometer design

Teacher/Technician notes

Designing a liquid in glass thermometer

This activity is intended to support teaching and learning. As a practical activity it can be credited towards the Practical Endorsement, particularly as it is intended to be investigative.

The Student sheet is provided in Word as an outline which can be amended to suit your particular requirements and the availability of equipment. Should you not have the curriculum time or equipment an alternative sheet allows for a class or homework based consideration of the factors involved.

Aim

To consider factors affecting the design of liquid in glass thermometers
To understand terminology of measurement

Specification

2.2.1(a) systematic and random errors
2.2.1(b) precision and accuracy
2.2.1(c) absolute and percentage uncertainties
5.1.1(a) thermal equilibrium
5.1.1(c) temperature measurements in degrees Celsius
5.1.3(a) specific heat capacity of a substance; the equation E = mcΔθ

Practical skills

1.2.1(a) apply investigative approaches and methods
1.2.1(b) safely and correctly use a range of practical equipment
1.2.1(d) make and record observations and measurements
1.2.1(e) keep appropriate records of experimental activities
1.2.1(f) present information and data in a scientific way
1.2.1(j) use a wide range of experimental and practical instruments, equipment and techniques
1.2.2(a) use of appropriate analogue apparatus
1.2.2(b) use of appropriate digital instruments

Apparatus

Test tubes
Boiling tubes
Small conical flasks
Medium conical flasks

Capillary tube
Glass tube
Bungs to allow each combination of tube and container
Food colouring
Water baths (minimum 2)
Ice
Beakers (sufficiently large to accommodate each) conical flask
Metre rules
Electronic balance
Bunsen burners
Tripods and gauzes

Health and safety

Having the glass tubes already fitted into the bungs reduces the time needed to complete this activity and reduces the risk of learners cutting themselves on broken glass
Learners should be specifically advised to insert the tubes by putting pressure on the bung and not the tube.
Care when using Bunsen burners and associated equipment

Setting the scene

The learners are challenged to ascertain the best combination of reservoir and expansion tube to make a liquid in glass thermometer to consider

a)Greatest precision for a temperature of 50°C

b)Being able to give a value between 20°C and 80°C

Expectations

Learners are likely to establish that:

1)A larger reservoir results in a larger volume of expansion

2)A larger volume of expansion gives greater discrimination of measurement

3)A wider bore in the glass tube gives a smaller difference in the position of the distance of the end of the column of coloured liquid after expansion

4)A wider bore reduces precision but increases the potential range of the thermometer

Learners may not consider that:

5)A larger reservoir will require more energy to raise its temperature to be in thermal equilibrium with the liquid being measured

6)The resulting temperature of the combined system with the liquid being measured and a large reservoir on the thermometer will be lower than if a smaller reservoir were used

Calibration and use

Learners may calibrate their thermometers using ice/water mixture, boiling water and/or water baths at two defined temperatures (say 40°C and 60°C). They can then calculate their scale and mark their tubes accordingly.One water bath can be at a temperature between 45°C and 55°C, with learners asked to use their thermometer to determine its temperature.

Student Sheet – Thermometer Design

Liquid in glass thermometers have a simple basis for their design.

A reservoir of liquid is placed in the liquid whose temperature is to be measured.

The liquid in the reservoir will expand as its temperature increases.

The expanding liquid fills a glass tube, allowing the observer to judge the distance the top of the column of liquid has travelled along the tube.

You have available a number of differing pieces of glassware to act as the reservoir; test tube, boiling tube and conical flasks.

You have available glass tubes with different diameter bore.

Investigate differing combinations of reservoir and tube to:

Make a thermometer which is best suited to the precise measurement of a beaker of water 50°C +/- 5°C.
Make a thermometer capable of measuring across the range from 20°C and 80°C.
Calibrate your thermometers for use using ice/water mixture and the two water baths at 40°C and 60°C. Use your thermometers to determine a value for the unknown water bath.

Document the measurements and observations that you make.

Write a clear explanation based on your observations, which gives a step by step justification of your conclusions.

Consider the impact of your designs on the response time for your thermometer and its accuracy in recording the temperature of the water.

As an extension consider the statement that it is impossible to make any measurement without having an effect on the value which is actually measured. In which circumstances is this most obvious? Are there any measurements made which are independent of an effect of the instrument on the measurement?

Alternative student sheet

Liquid in glass thermometers have a simple basis for their design.

A reservoir of liquid is placed in the liquid whose temperature is to be measured.

The liquid in the reservoir will expand as its temperature increases.

The expanding liquid fills a glass tube, allowing the observer to judge the distance the top of the column of liquid has travelled along the tube.

You have available three differing pieces of glassware to act as the reservoir, a boiling tube and two conical flasks.

You have available glass tubes with different diameter bore.

Consider the effects of differing combinations of reservoir and tube to:

Make a thermometer which is best suited to the precise measurement of a beaker of water 50°C +/- 5°C.
Make a thermometer capable of measuring across the range from 20°C and 80°C.
Comment on how the options available for reservoir and expansion tube affect the precision, range, accuracy and time of response of the thermometer.

Document the measurements and observations that you would make to substantiate your comments and to calibrate the scale on your thermometer.

Write clear explanations which give a step by step justification of your conclusions.

Field and particle physics