Thermal Physics

Question 1

what is heat energy?

Answer 1

a form or energy that is transferred as a result of temperature differences

Question 2

what is temperature?

Answer 2

the measure of the average kinetic energy of particles in a body
kelvin, K
t(K) = T(^C) + 273

Question 3

adv. and disadv. of thermocouple

Answer 3

1. able to measure temp. at a point
2. more accurate since its made from parts of low thermal capacity
3. can be remotely controlled
4. sensitive to small temp. changes
   - non-linear scale

Question 4

what is a thermometer?

Answer 4

a device used to measure temperature of a body

Question 5

thermometric property

Answer 5

a physical property that changes regularly with change in temp.
- thermal exp. of metal (bi - metallic strip)
- exp. of a liquid ( liquid-in-glass thermometer)
- exp. of a gas ( constant gas thermometer)
- e.m.f. between 2 points ( thermocouple
- resistance of a conductor ( resistance thermistor)
- wave length ( pyrometer)

Question 6

qualities of a good thermometer

Answer 6

responsive - how fast it indicates change in temp.
sensitivity - degree to which physical property of thermometer changes for small changes in temp.
range - difference between highest and lowest temp. it can measure
linearity - thermometric property changes consistently for a change in temp.

Question 7

parts of a thermocouple

Answer 7

• voltmeter (measures energy difference)
• metal x, metal x
• metal y
• hot junction
• cold junction

Question 8

common liquids used in liquid in glass thermometer + diagram

Answer 8

• mercury
• alcohol
  1. thin capillary bore with uniform diameter
  2. thick glass stem
  3. linear scale
  4. kink
  5. large bulb

Question 9

linearity, sensitivity, responsiveness, range (liquid-in-glass)

Answer 9

linearity - bore has uniform diameter
sensitivity - thin capillary
bore increases
sensitivity
- large bulb to
push up more
liquid
responsiveness - thin glass lining
range - long capillary bore
- increase diameter
of bore

Question 10

why isnt water used in a thermometer?

Answer 10

water cannot expand as much as e.g. mercury so calibration requires 2 fixed points

Question 11

properties of solids

Answer 11

• particles packed closely together in lattices
• particles held together by strong intermolecular forces
• particles vibrate about mean position
• form rigid, incompressible structure

Question 12

properties of liquids

Answer 12

• particles further apart than solids
• particles held together by weak intermolecular forces
• particles slide past each other
• liquids incompressible

Question 13

properties of gases

Answer 13

• particles far apart
• no intermolecular forces
• highly compressible

Question 14

what is internal energy

Answer 14

the sum of random distribution of the kinetic and potential energy of particles in a body
U = Ek + Ep

Question 15

kinetic theory of matter

Answer 15

matter is made up of tiny particles that are in constant random motion

Question 16

what is thermal capacity?

Answer 16

the energy required to raise the temp. if a body by one degree or kelvin
J/^C
C = E/ change in temp.
C = P x t / change in temp.
C = I V t/ change in temp.

Question 17

what is specific heat capacity?

Answer 17

the energy required to raise the temp. of a 1kg mass of a body by 1 degree celsius
J/ kg^C
c = E / m x change in temp.
c = P x t / m x change in temp.
c = I x V x t / m x change in temp.

Question 18

what is latent energy?

Answer 18

a form of energy that enables bodies to change their state of mater at a constant temp.

Question 19

what is specific latent heat?

Answer 19

the energy required to change the state of a 1kg mass at constant temp.
J/ kg OR J/g
L = E / m OR L = E / m OR
L = IVt / m

Question 20

what is specific latent heat of fusion?

Answer 20

the energy required to change a 1kg mass of solid to a liquid at constant temp.

Question 21

what is specific latent heat of vapourisation?

Answer 21

the energy required to change the state of a 1kg mass of liquid to gas at a constant temp.

Question 22

what is boiling?

Answer 22

a change in state from liquid to gas at a constant temp.

Question 23

similarities and differences of boiling and evaporation

Answer 23

S
1. they both change state from liquid to gas
2. they both require heat
D
1.boiling is more volatile
2.boiling happens through the liquid whereas evaporation happens at the surface
3.boiling happens at a constant temp. whereas evaporation takes place at any temperature

Question 24

what is melting?

Answer 24

a change in state from solid to liquid at a constant temp.

Question 25

what is evaporation?

Answer 25

a change in state from liquid to gas at any temp.

Question 26

what is conduction?

Answer 26

a means of energy transfer through solids

Question 27

what is convection?

Answer 27

means of heat transfer through fluids

Question 28

what is radiation?

Answer 28

heat energy is transferred by means of electro magnetic radiation

Question 29

what is charles’ law?

Answer 29

for a fixed mass of gas, volume is directly proportionals to absolute temperature if pressure is kept constant

Question 30

what is pressure law?

Answer 30

for a fixed mass of gas, pressure is directly proportional to absolute temperature if volume is kept constant

Question 31

what is boyle’s law?

Answer 31

for a fixed mass of gas, volume is inversely proportional to pressure if temperature is kept constant