Expansion and Thermometers Flashcards

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1
Q

What happens when a material is heated ?

A

It expands

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2
Q

Examples of thermometers (5)

A
Lab thermometer 
Infrared thermometer
Clinical thermometer 
Constant volume gas thermometer
Thermocouple
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3
Q

Define thermometer

A

an instrument used to measure temperature

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4
Q

Fixed points on the celcius scale

Define upper fixed point

A

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

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5
Q

Fixed points on the celcius scale

Define lower fixed point

A

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

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6
Q

TRUE/FALSE

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

A

TRUE

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7
Q

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

A

-10C to 110C

OR

0C to 100C

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8
Q

Temperature range for clinical thermometer

A

34C/35C to 43*C

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9
Q

Temperature range for a thermocouple

A

-250C to about 1500C

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10
Q

Most thermometers used in school are a ______

A

liquid in glass lab thermometer

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11
Q

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

Give at least 2

A

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.

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12
Q

State one use of lab thermometers

A

In school for lab experiments

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13
Q

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

A

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.

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14
Q

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

A

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

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15
Q

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

A

Thermometric

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16
Q

State how a thermometer calibrated

A

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.

17
Q

Expansion in terms of kinetic theory

Explain expansion in solids

A

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

18
Q

Expansion in liquid and gases

A

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.

19
Q

Application of thermal expansion
for example,

power lines

opening jars

creaking roofs.

A

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.

20
Q

Bimetallic strip can be used in

A

simple fire alarm

21
Q

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

A

brass

invar

22
Q

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

A

Brass

invar

23
Q

Explain thermal expansion

A

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