thermal effects Flashcards
(34 cards)
1
Q
conduction
A
- particles move from high temp to low temp without the particles of the objects moving positions
- materials that allow energy to easily travel through them are conductors
- metals have free electron which help transfer heat more rapidly by conduction, some metals have more free electrons
- not possible for heat to travel by conduction through a vacuum as no particles a present, vacuums are used to stop heat flow by conduction in thermos flasks
- most liquids are poor conductors, gases are the worst heat conductors, great insulators though
2
Q
convection
A
- transfer of heat in a fluid by the actual movement of the fluid particles
- energy flows through a fluid from a place of high temp to low temp by the movement of fluid particles.
- convection current is made visible in water by placing something coloured
- movement of liquid driven by a heat source is called convection currents.
3
Q
radiation
A
- radiation is an electromagnetic emission by any surface at a temperature greater than absolute 0. the hotter the surface the more heat radiation it emits
- the electromagnetic spectrum consists of different parts. infra-red radiation is part of the electromagnetic spectrum that transfer thermal energy
4
Q
infra-red characteristics
A
- does not involve the movement of particles and is therefore the only means by which heat can travel through a vacuum
- travels in straight lines and travels at the same speed as light (3x10^8)
- it warms the object that absorbs it
- invisible to the eye but can be detected by nerve cells in skin
5
Q
absorbers and emitters of radiation
A
- when infra-red strikes the surface of an object some of it will be absorbed, making the object warmer; some of it will be reflected.
- light coloured and smooth surfaces cause the most radiation to be reflected
- dark coloured and rough surfaces cause most radiation to be absorbed
6
Q
solid
A
- definite shape and volume
- arranged in a rigid regular pattern (lattice)
- small particle spaces particles vibrate only in fixed positions and have low kinetic energy
- strong attractive forces
- cannot compress
7
Q
liquid
A
- no definite shape but definite volume
- no fixed structure or regular arrangement
- small particle spaces
- particle groups can squeeze between each other (flow) and have more kinetic energy than solid particles
- strong attractive forces
- cannot compress
8
Q
gas
A
- no definite shame or volume
- no fixed structure
- very large particle spaces
- particles free to move randomly and have lots of kinetic energy
- no attractive forces
- easy to compress
9
Q
brownian motion
A
the constant, random motion of fluid particles.
observing smoke particles under a microscope provides evidence of brownian motion. particles appear to move bout in a wandering zip-zag fashion as they are constantly bombarded by very small, fast moving invisible air (gas) particles
10
Q
diffusion
A
the spreading out of a substance due to its constant random motion.
molecules of one substance move between the molecules of another. diffusion is evidence that gas molecules move.
11
Q
evaporation
A
process of a liquid turning into a gas below its boiling point
12
Q
how evaporation happens
A
in a liquid some particles have more energy than others. particles on the surface are able to escape and form gas
13
Q
evaporation has a cooling effect
A
- as the faster particles escape from a liquid the slower ones are left behind, therefore the average kinetic energy of the molecules remaining decreases-temperature decreases
- thermal energy will be removed from a body in contact with the evaporating liquid, as the temperature of the liquid continues to decrease
14
Q
evaporation has a cooling effect
A
- as the faster particles escape from a liquid the slower ones are left behind, therefore the average kinetic energy of the molecules remaining decreases-temperature decreases
- thermal energy will be removed from a body in contact with the evaporating liquid, as the temperature of the liquid continues to decrease
15
Q
factors that speed up evaporation:
A
- increase temperature
- increase surface area
- blow air across surface
16
Q
how boiling differs
A
rapid form of evaporation which only occurs when the liquid reaches its boiling point. particles in the liquid are given so much energy that they form a gas throughout the liquid (bubbles)
17
Q
melting
A
- when a solid is heated the average kinetic energy of the particles increase an the particles vibrate more violently
- if enough heat is added to break the attractive forces between the particles the solid will melt.
- while the solid is melting the extra energy is put into the breaking the binds and not continuing to make the particles vibrate faster. this causes the temperature to remain constant while the solid is melting.
18
Q
boiling
A
- when a liquid is heated the same effect is seen- particles gain kinetic energy and the temperature of the liquid increases. eventually they gain sufficient energy to escape the liquid and go into the gaseous state
- during boiling all the heat energy supplied to the liquid goes into breaking the bonds between particles. hence, the temperature remains constant when the liquid boils
19
Q
latent heat
A
- the heat energy that must be added or removed when a substance changes state without a change in temperature. the latent heat does not increase temperature but goes into breaking the attractive forces between the particles so it can change state
20
Q
types of latent heat
A
- specific latent heat of fusion Lf
of a substance is the amount of energy needed to melt 1kg of the solid to liquid without changing temperature - specific latent heat of vaporisation Lv
of a substance is the amount of energy needed to boil 1kg of liquid to gas
without changing temperature
21
Q
factors to consider while dealing with gas:
A
- volume
- temperature
- pressure
22
Q
gases at constant temperature - boyles law:
A
- decreasing the volume of a gas will increase its pressure- more particles in the given are so more frequent collision with container walls
- the relationship is inversely proportional- if the volume halves the pressure doubles, vice versa
- a plot of 1/volume against pressure gives a straight line through origin
the relationship is boyles law - for a fixed mass of gas at constant temperature the pressure is inversely proportional to its volume
23
Q
boyles law
A
- if a gas is heated but kept at a constant volume the pressure increases
- of a gas is heated but kept at a constant pressure the volume increases
24
Q
specific heat capacity
A
- heat is energy that passes from high temp to low temp
- matter does not contain heat
- amount of energy needed to raise the temperature of 1kg substance by 1 C
unit of heat capacity= J / (kg C)
25
thermal capacity
- ome foods remain hotter than others - different substances have different capacities
longer time to change temperature means bigger thermal capacity
26
thermal capacity
- ome foods remain hotter than others - different substances have different capacities
longer time to change temperature means bigger thermal capacity
27
temperatures and thermometers:
- temperature is a measure of average kinetic energy of all the particles in a substance
- the more kinetic energy the particles possesses the faster they move and the higher the temperature
- different from heat which is tether total amount of thermal energy an object possesses
- two objects can have the same temperature but different amounts of heat
- temperature is measured by a thermometer
- a scale and unit of temperature are obtained by choosing two temperatures, called the fixed points and dividing the range between into a number of equal divisions
28
celsius scale
- units are degrees Celsius
- the lower fixed point ( ice point) = a temperature at which pure ice melts (0C)
- the upper fixed point ( steam point) = the temperature at which pure water boils under normal atmospheric pressure 100kPa = 100 C
29
Kelvin scale
- based on the average kinetic energy of particles
- lowest point on the kelvin scale is 0K which is -273 C. this theoretical point is called the absolute zero and is the point where particles have no energy and stop moving
30
thermometers
- the sensitivity of a thermometer indicates the size of movement per degree change of temperature. a thermometer is sensitive when a small change of temperer produces a bit detectable change in the reading
- the range of a thermometer is the number of units between the lowest and highest readings on the scale of the given thermometer. the range on a clinal thermometer is given from 35 C- 42 C which is a range of only 7 C. a laboratory thermometer would have a larger range -4 C- 110C. a smaller range increases the sensitivity of the thermometer
31
liquid in glass thermometer
- liquid in the glass bulb at the base expands up a very thin capillary when the bulb is heated
- there is a vacuum in the tube above the liquid so it can easily move along the tube
32
properties of liquid in glass thermometer
- linearity- must expand evenly
- responsive- must expand rapidly by a large amount over a wide range
- ,kist not stick to the inside of the tube
- must be clear and visible
- mercury and coloured alcohol have these properties and hare commonly uses
- to make a liquid-in-glass thermometer more sensitive the tube in the centre of the thermometer must be very narrow so a small change in temperature causes the liquid to move a long way up the tube
33
thermocouple thermometer:
- two different metals are joined at two conjunctions. a temperature difference between the junctions causes tiny voltage which makes current flow. they can be linked to electrical circuits
- thermocouples have higher responsiveness and a wider range than liquid-in-glass thermometer
34
thermistor thermometer
- a device which becomes a better electrical conductor when its temperature rises ( resistant decreases)
- higher temperature causes higher current and reading on the meter
