IB HL Physics - TPNoM 4,5

System

The body or bodies that we are considering

Surroundings

The area that the system can interact with through the transfer of heat energy

Universe

The system and it’s surroundings

Open System

a system which can exchange energy, work done, and matter with its surroundings

Closed System

a system which can only exchange work done and energy with its surroundings

Isolated System

a system which cannot exchange anything wit it’s surroundings

The First Law of Thermodynamics

The Thermal energy (Q) entering a closed system is equal to the sum of the Change in Internal Energy (ΔU) of the system and the Work Done (W) of the system

Q=ΔU+W

IsoBaric Change

• a change in state where pressure is constant (ΔP=0)

• temperature and volume change proportionally

• Work is done on or by the gas to change the volume

IsoVolumetric change

• a change in state where volume is constant (W=0)

• temperature and pressure change proportionally

• Q=ΔU+0

IsoThermal Change

• a change in state where temperature is constant (ΔU=0)

• pressure and volume are inversely proportional

• Q=0+W

• ideally an isothermal change is infinitely slow

Adiabatic Change

• a change in state where no thermal energy is transferred (ΔU=0)

• volume temperature and pressure can change

• the magnitude of ΔU will be equal but opposite to the W

  • +W = -ΔU

  • -W = +ΔU

• when ΔU is positive temperature increases

Entropy (S)

a measure of the number of possible arrangements of the particles and their energies

The Second Law of Thermodynamics

The entropy of the universe always increases during an irreversible change

The Clausius Clause

Energy cannot be transferred from a body at lower temperature to a body at a higher temperature unless work is done system

Kelvin’s Clause

Energy cannot be extracted from a hot object and transferred entirely into work

Heat Engine

a device that converts thermal energy into mechanical work by transferring heat from a hot reservoir to a cold reservoir

Reversible Process

a process in which there is no overall change in the entropy of the system and its surroundings

Irreversible process

a process which results in an overall increase in entropy of the system and its surroundings

Microstate

a specific molecular configuration

Macrostate

larger scale measurable outcome, resulting from the outcome of each of the smaller microstates

Equations of Entropy

• S= K_B ln(Ω)

• ΔS=ΔQ/T

Stages of a Heat Pump

1. Thermal energy is transferred from the hot reservoir into the heat engine

2. The volume of the system increases because the system does work on the surroundings

3. Some of the thermal energy from the hot reservoir is transferred into the cold reservoir

4. The surroundings do work on the system and the volume decreases allowing the process to restart

Carnot cycle

T₁>T₂

1. Thermal energy is supplied to the gas at T₁ and isothermal expansion takes place Q=W

2. Adiabatic expansion takes place Q=0, ΔU=-W internal energy is used for work on surroundings and T₁ decreases to T₂

3. Isothermal compression takes place Q=W work done on system and energy Q is rejected because T is constant at T₂

4. Adiabatic compression, work done on gas increases T₂ to T₁

Ion

particles with different numbers of electrons and protons

Elementary charge (e)

the magnitude of the charge of a proton or electron

1e = 1.60×10^-19C

Potential Difference (V)

The work done per unit charge moving at a positive charge between two points

Electromotive force (emf)

work done by a cell per unit charge

Electron Volt (eV)

the energy gained when an electron is accelerated by a potential difference of 1 volt

W=qV

1eV=1.6×10^-19 J

Conventional current (I)

the amount of positive charge flowing past a point in a second

Conventional current and electron flow

CC= + → -

EF = - → +

Electrical Resistance (R)

the ratio of potential difference across a component to current through it

Electrical Power

rate of energy transfer (amount of work done per second)

Ohm’s Law

that potential difference across a metallic conductor is proportional to the current flowing through it, provided the temperature does not change

Non-Ohmic Conductors - Filament Lamp

• As pd across the filament lamp is increased, the electrons collide more frequently with the vibrating fixed ions, transferring energy

• temperature increases which makes resistance increase

Non-Ohmic Conductors - Semi-conducting Diode

• Diodes only allow current to flow in one direction

• for negative V values there is no current

• there is no significant current in the forward direction before the threshold voltage

• high then low resistance in the forward direction

LDRs and Thermistors

• LDR - resistance is inversely proportional to light intensity

• NTC Thermistor (negative temp coeff.) - resistance is inversely proportional to temperature

Resistance of Wires

The physical propertied of a wire change it’s resistance

• Length

• Cross sectional area

• Resistivity

R=ρL/A

Kirchoff’s First Law

The sum of currents into a junction is equal to the sum of currents out of a junction

Kirchoff’s Second Law

in a complete loop the sum of emfs is equal to the sum of potential difference in a loop