Heat and Temperature Flashcards Preview

LC Physics > Heat and Temperature > Flashcards

Flashcards in Heat and Temperature Deck (30):
1

Conductor

A material which allows energy to pass through it
/
A material which is able to conduct heat and/or electricity

2

Heat

Energy possessed by an object due to the kinetic energy of its atoms or molecules

3

Temperature + how its measured

A measure of the 'hotness' of a substance
Measured in °C (celsius)

4

Thermometric property

A physical property that changes measurably with temperature

5

Standard Unit (SI) of temperature

Kelvin (K)
represented by T in questions

6

Practical unit of temp

The degree Celsius (°C)
represented as t in questions

7

converting celsius and kelvin

°C = K - 273.15

t = T - 273.15

8

Thermometric properties

1. Length of a column of liquid
2. E.m.f of a thermocouple
3. Pressure of a gas at constant volume
4. Resistance
5. Colour
6. Thermometers

9

length of a column of liquid eg. mercury thermometer

Liquid expands when heated, it's trapped in narrow column up middle of the thermometer, so the only place it can go is either up when heated or down when cooled

10

E.m.f of a thermocouple

-E.m.f is the electromotive force ( a small voltage)
-Thermocouple is two diff metals joined together (copper + iron?)
-One junction is kept in a hot area, + other one is the cooler area
-The bigger the temp diff, the bigger the emf (measured in millivoltmeter)

11

Pressure of a gas at constant volume

-Take a glass gas syringe, put it face down in a beaker w/ weights on top of piston
-The greater the rise in temp, the more weights needed to keep the volume constant as gas expands when heated

or

Take a glass gas syringe, put an air tight seal on end
once a constant volume has been set
-As gas is heated, expands + piston is pushed out

12

Resistance

-Electrical resistance of a conductor increases as temp increases
-Resistance of a semiconductor decreases w/ increasing temp
-A thermistor uses resistance

13

Colour

There are crystals in the strip that change colour with increasing temp

14

Thermometers

-Thermometers measure temp
-They will agree @ freezing + boiling point (0°C and 100°C) but two thermometers do not necessarily give the same reading at other temps (called Disagreement)
-Therefore, there is a need for standard thermometers, we use a commercial laboratory mercury thermometer as school standard

15

Using a thermometric property to measure temperature

-Graduate two thermometers at ice and steam points
-Compare values obtained for an unknown temp, using a straight-line graph between the reference points

16

Practical thermometers

-Practical thermometers eg. clinical thermometer
-Infra-red radiation thermometer
-Plastic strip thermometer
Oven thermometer
Boiler thermometer
Temperature gauge in a car

17

Heat capacity

The amount of heat energy needed to change the temp of an object by 1 C / 1 K

18

Symbol for heat capacity

C

19

Unit for heat capacity

joule per Kelvin (J K⁻¹)

20

Formula for heat energy

Heat energy = heat capacity x change in temperature

Q = CΔθ

21

Heat energy to raise and given out as temp falls

The amount of heat energy needed to raise the temp of an object by 1°C (1 K) is the same as the amount of heat energy given out if its temp falls by 1°C (1 K)

22

Specific Heat Capacity

amount of heat energy necessary to change the temp of 1kg of a subdtance by 1°C (or 1K)

23

Specific heat capacity symbol + unit

sumbol: c

Unit: joule per kilogram per Kelvin ( J kg⁻¹ K⁻¹ )

24

Heat energy added/lost formula

mass x specific heat capacity x rise in temp

25

Real world applications of specific heat capacity

Storage heaters use concept of SHC, are warmed at night when it is cheaper to use electricity, and give out heat gradually during day. Contain bricks which release heat stored in them.

26

Latent heat of a substance

the heat energy neeed to change its state without a change in temp.
eg. solid to liquid (dry melting ice)

27

Latent heat symbol + unit

Symbol: L

Unit: joule (J)

28

perspiration

As perspiration evaporates, it takes latent heat from our bodies + cools us down

29

perfume

-Same thing happens if you spray perfume on your skin, or spill methylated spirits on yourself
-Liquid takes its latent heat from your body, making you feel cool in that area

30

specific latent heat of a substance

the amount of heat energy needed to change the state of 1kg of that substance w//o a change in temp