DAY BEFORE THERMAL PHYSICS

Question 1

what is meant by internal energy

Answer 1

• the sum of randomly distributed potential and kinetic energies of particles in a body

Question 2

how can internal energy be increased

Answer 2

• doing work on system
• adding thermal energy to it

Question 3

how can internal energy be decreased

Answer 3

• losing thermal energy to surroundings
• system doing work on surroundings

Question 4

whats the 1st law of thermodynamics

Answer 4

“internal energy of a system can be increased when energy is transferred to it by heating or when work is done on it”

Question 5

explain compressing the gas

Answer 5

• work being done ON gas
• internal energy of particles increases
• particles have a greater average KE

Question 6

explain gas expanding

Answer 6

• work being done BY gas ON surroundings
• internal energy of gas decreases
• average KE of particles decreases

Question 7

define specific heat capacity

Answer 7

• the amount of thermal energy required to change the temperature of 1kg of a substance by 1K, without changing state

Question 8

define specific latent heat

Answer 8

the amount of thermal energy required to change the state of 1kg of a substance without changing temperature

Question 9

whats equation for continious flow rate for c

Answer 9

Q2 - Q1 / ( m2 - m1) delta temp

Question 10

define specific latent heat of fusion
define specific latent heat of vaporisation

Answer 10

• thermal energy required to convert 1kg of a solid into a liquid, without change in temp
• thermal energy required to convert 1k of a liquid into a gas, without a change in temp

Question 11

explain the slopes and flats on a T - I graph

Answer 11

slopes : temp is changing as we reach temp for melting / evaporation, average KE of particles increases

flats : temp constant, but bonds break/ form so potential energy increases

Question 12

define absolute zero

Answer 12

• temp at which molecules have 0 kinetic energy

Question 13

whats Boyle’s Law

Answer 13

at a constant temp, pressure inversely proportional to volume

p1v1 = p2v2

Question 14

whats Charle’s Law

Answer 14

at a constant pressure, volume is proportional to temperature

v1/t1 = v2/t2

Question 15

whats pressure law?

Answer 15

• at a constant volume, pressure is proportional to temperature

p1/t1 = p2/t2

Question 16

what an ideal gas

Answer 16

gas that obeys pV ~ T

Question 17

why high temp high pressure

Answer 17

• temp is a measure of average KE of particles
• temp ~ KE
• increasing temp increases velocity of particles
• change in momentum is greater hence force greater
• pressure is force per unit area, pressure increases

Question 18

why smaller volume higher pressure

Answer 18

• smaller volume means particles collide more frequently
• pressure is force per unit area
• more force ( due to change in momentum ) hence more pressure

Question 19

work done by a gas?

Answer 19

pressure x change in volume

Question 20

equations for ideal gases

Answer 20

pV = nRT
pV = NkT

Question 21

whats internal energy for an ideal gas?

Answer 21

U = N x Ek

as no intermolecular forces

Question 22

how to calculate molar mass

Answer 22

mass / number of moles

Question 23

what are assumptions for derivation?

Answer 23

• no intermolecular forces
• time of collision is negligible compared to time between
• volume or molecule negligible compared to container
• elastic collisions