Expansion and Thermometers

Question 1

What happens when a material is heated ?

Answer 1

It expands

Question 2

Examples of thermometers (5)

Answer 2

Lab thermometer 
Infrared thermometer
Clinical thermometer 
Constant volume gas thermometer
Thermocouple

Question 3

Define thermometer

Answer 3

an instrument used to measure temperature

Question 4

Fixed points on the celcius scale

Define upper fixed point

Answer 4

Upper fixed point (100*C) is the temperature of steam from pure boiling water at standard atmospheric pressure

Question 5

Fixed points on the celcius scale

Define lower fixed point

Answer 5

Lower fixed point - (0*C) is the temperature of pure melting ice at standard atmospheric pressure

Question 6

TRUE/FALSE

The freezing point of water is the same as the melting point of ice: (0°C).

Answer 6

TRUE

Question 7

Temperature range for a liquid/mercury-in-glass/lab thermometer.

Answer 7

-10C to 110C

OR

0C to 100C

Question 8

Temperature range for clinical thermometer

Answer 8

34C/35C to 43*C

Question 9

Temperature range for a thermocouple

Answer 9

-250C to about 1500C

Question 10

Most thermometers used in school are a ______

Answer 10

liquid in glass lab thermometer

Question 11

Explain the design of a lab thermometer which makes it suitable for its particular task (4)

Give at least 2

Answer 11

1) Bulb that holds mercury has a thin wall so that heat can easily transfer through it.
2) The scale is positioned very close to the bore to reduce parallax error
3) The bore is very narrow so that any change in volume of the mercury will result in a noticeable change in the length of the mercury thread.
4) The bulb is relatively large so that the corresponding expansion or contraction of the mercury it contains is noticeable for small changes in temperature.

Question 12

State one use of lab thermometers

Answer 12

In school for lab experiments

Question 13

Explain the design of a clinical (mercury) thermometer which makes it suitable for its particular tasks

Answer 13

The scale ranges only from 34C or 35C to 43C because the normal body temperature of a human is 37C

2) The interval between markings on the scale is 0.1*C so that a very precise reading is obtain.
3) There is a narrow constriction in the bore. When the thermometer is removed from the patient, the body heat causes the mercury in the bulb to heat up, expand and rise up the capillary tube, through the constriction up to a certain level to indicate the body temperature. The constriction breaks the liquid thread (to prevent the mercury from flowing back into the bulb) and allows the temperature to be read.

Question 14

Explain the design of a thermocouple which makes it suitable for its particular task

Answer 14

It is electrical - can be connected to digital displays and computer systems

Question 15

A property of a material which varies with temperature. ______ property

Answer 15

Thermometric

Question 16

State how a thermometer calibrated

Answer 16

The values of the thermometric property at upper and lower fixed points are found and marked on the thermometer and the interval between the fixed points is then calibrated.

Question 17

Expansion in terms of kinetic theory

Explain expansion in solids

Answer 17

When a solid is heated, the heat energy supplied converts into kinetic energy of its particles(thermal energy). The molecules of the solid vibrate faster with greater amplitude and therefore occupies more space

Question 18

Expansion in liquid and gases

Answer 18

When a liquid or gas is heated, the heat energy supplied converts to kinetic energy of its particles. The molecules of liquid and gas translate faster and therefore occupy more space.

Question 19

Application of thermal expansion
for example,

power lines

opening jars

creaking roofs.

Answer 19

Power lines must be laid slack in summer so that strong tension forces are not produced when they contract in winter

Roofs shrink at night as temperature falls. Contraction of the wood causes the joints to move relative to each other producing a creaking sound

A tight metal lid on a glass jar is easily removed by running hot water unto it. The lid rapidly expands due to its high thermal conductivity and becomes loose.

Question 20

Bimetallic strip can be used in

Answer 20

simple fire alarm

Question 21

The two metal strips in a bimetallic strip are ____ and ____

Answer 21

brass

invar

Question 22

____ expands more than ____ when heated and so this combination forms a good bimetallic strip. It will also contract more on cooling.

Answer 22

Brass

invar

Question 23

Explain thermal expansion

Answer 23

When a material is heated the particles gain thermal energy. In a solid this increase in energy causes the particles to vibrate more while staying in the same position. This increase in vibration will force the particles slightly further apart and as a the material expands