Topic B

Internal energy

Total energy in a substance (sum of kinetic energy and potential energy)

Conduction

Transfer of energy through particle vibration in solids, liquids, and gases. The hotter the object, the greater the vibrations

Convection

Transfer of heat that only occurs in liquids or gases. Particles become less dense and rise when they get more energy. Heat flows from an area of high concentration to an area of lower concentration.

Radiation

The movement of heat by infrared waves

Relationship between intensity and wavelength (Black body radiation)

Intensity increases as the wavelength decreases, reaches a peak, and then decreases with further decreases in wavelength

Luminosity

Describes how much light is emitted from the source, which does not change regardless of where we observe it.

Ideal gases (things that are different to real gases)

• No intermolecular forces between molecules (U = KE only)

• Collisions with other molecules/walls are totally elastic (no KE is lost)

• Cannot change phase

• Newton’s Laws apply

• Collisions are instantaneous (no time taken)

• Particles are treated as infinitely small points (a sphere)

First law of thermodynamics

Q = ΔU + W
Thermal energy transferred to a gas has to equal the sum of the work done by the gas and its increase in internal energy

Isobaric

ΔU = Q - W
W = PΔV

V₁/T₁ = V₂/T₂

Constant P

Isovolumetric

W = 0
ΔU = Q
P₁/T₁ = P₂/T₂

Constant V

Isothermal

ΔQ = 0

Q = W

P₁V₁ = P₂V₂

Constant T

Adiabatic

ΔU = -W

Q = 0

PV^5/3 = Constant

TV^2/3 = Constant

Cyclic process

Series of transformations that takes a gas back to its original state

The second law of thermodynamics

ENTROPY.

• The spreading out of energy

• It is not possible for a heat engine working in a cycle to absorb thermal energy and transfer it all to work.

Current (I) [A]

The rate of flow of charge; or the amount of charge passing through a point in the circuit every second

Direct current (DC)

Refers to when the current flows in one direction at a constant rate

Alternating current (AC)

Refers to when the current fluctuates between positive and negative (the current travels in both directions)

Voltage (V) [V]

Work done carried by every unit of charge

Series circuit

There is only one path of travel, hence current is constant along every point of the branch.

Parallel circuit

At a junction, the truck has a choice of which branch to take, and they tend to choose the path with less resistance. The branch shares the current according to the ratio of the total resistance across each branch.

Ohm’s Law

The voltage across a conductor is directly proportional to the current at a constant temperature.