13. Heat conduction, diffusion, fluids

Question 1

What is heat conduction

Answer 1

• the flow of energy to eliminate temperature differences

* ie. the constant heat loss from our bodies through our skin at moderate temperatures

Question 2

How do you calculate the number of accessible microstates of the system?

Answer 2

• S = Kb*ln(W)
S - entropy
Kb - botzmann’s constant
W = number of accessible microstates of the system

Question 3

When is the entropy of a system highest? Why?

Answer 3

When at equilibrium
•In an isolated system, when the system’s entropy reaches the maximum, the system stays there
•because any further change would reduce entropy

Question 4

What can closed and open systems exchange?

Answer 4

Closed:
• exchange heat

Open
• heat and matter

Question 5

What is the material constant λ? Unit?

Answer 5

λ is the thermal conductivity coefficient

•unit - J/(m.s.K)

Question 6

Why is λ always positive?

Answer 6

λ (Thermal conductivity coefficient) always positive as heat always flows from an area of high temperature to one with lower temperature

Question 7

Why is it easier to cut an ice cube using copper than aluminium?

Answer 7

• copper has a higher thermal conductivity

* gains heat more easily and speeds up the melting process

Question 8

Passive diffusion

Answer 8

Allows small ions and molecules to penetrate the membrane in the direction from higher to lower concentration

Question 9

Active ion transport

Answer 9

These processes require energy, typically via ATP, to transport ions such as sodium and potassium across cell membranes

Question 10

What is observed in Fick’s law of diffusion?

Answer 10

The rate of a gas passing through a membrane of contact area A and width L is proportional to A, and the density difference on both sides of the membrane

Question 11

What is an ideal stationary fluid?

Answer 11

A fluid that has

•no internal friction or viscosity and is •incompressible (both volume and its density are constant)

Question 12

What are the forces acting on an ideal stationary fluid?

Answer 12

• the weight of the fluid directed downward
• contact forces
- fluid below the element pushes the fluid element upwards
- fluid above the element pushes the fluid element downwards

Question 13

What is Pascal’s law?

Answer 13

States that the difference between pressures at two different positions in a fluid of constant density is proportional to the vertical distance between these 2 positions

p2 - p1 = -pg (y2-y1)