Topic B - The particulate Nature of Matter

Intermolecular forces

Attractive (or repulsive) forces that exist between the molecules of a substance.

Thermal expansion

When an object is heated, its particles move further away from each other, and the volume of the object increases.

Kinetic energy

The energy stored in a moving mass.

Internal energy

The sum of kinetic energy and intermolecular potential energy.

Density

The mass of a substance divided by its volume.

Absolute zero

The lowest possible temperature (0 K) at which the pressure and volume of a gas are zero and the particles have zero kinetic energy.

Absolute temperature

The temperature using the Kelvin scale.

Specific heat capacity

The amount of energy required to increase the temperature of 1 kg of a substance by 1 °C.

Specific latent heat of fusion

The amount of energy required to change the phase of 1 kg of a substance at constant temperature from solid to liquid.

Specific latent heat of vaporization

The amount of energy required to change the phase of 1 kg of a substance at constant temperature from liquid to gas.

Thermal equilibrium

The process of heat moving from one area to another until both areas are balanced with the same amount of thermal radiation.

Thermal energy transfer

Occurs whenever there is a difference in temperature between two bodies.

Conduction

The transfer of thermal energy due to collisions between particles that are in direct contact with each other.

Conductors

A material that easily transfers thermal energy by conduction.

Convection

The transfer of thermal energy due to the mass movement of molecules.

Vacuum

A volume of space which contains no molecules.

Intensity

The power transferred per unit area.

Black body

An object that absorbs all the energy of all the wavelengths of electromagnetic spectrum that are incident upon it.

Luminosity

The amount of energy a black body emits per second.

Apparent brightness

A measure of how bright a star appears, measured by the amount of energy received per square metre per second by an observer on Earth.

Emissivity

A measure of the effectiveness of a surface to emit thermal radiation.

Macroscopic system

A system with objects that can be seen with the unaided eye.

Albedo

A measure of the fraction of solar radiation that is reflected off a macroscopic system compared to the total incident radiation.

Solar constant

A measure of the amount of solar electromagnetic radiation reaching the Earth's outer atmosphere per unit area per second.

Electromagnetic spectrum

The range of frequencies of electromagnetic radiation.

Factors affecting Albedo of earth

The thickness of the clouds above the Earth, latitude, and the type of terrain on the Earth's surface.

Latitude

How far north or south of the Equator a place is, measured in degrees with 0° being the equator and 90° being the North or South Pole.

Greenhouse gases

Gases in the atmosphere that absorb infrared radiation directly from the Sun and from the surface of the Earth.

Greenhouse effect

The absorption of thermal energy in the Earth surface-atmosphere system due to occurring concentrations of greenhouse gases in the atmosphere.

Pressure

A measure of the force which the particles in a container exert on the surface as the particles collide with it.

Ideal gases

Gases that are assumed to consist of particles that have negligible volume and negligible attractive forces.

Assumptions of the ideal gas model

The particles in a gas are in constant, random, straight-line motion. There are negligible forces of attraction (intermolecular forces) between the particles. Collisions between particles or with the walls of the container are perfectly elastic (no energy is lost). The distance between the particles is much greater than the size of the particles, therefore, gas particles have negligible volume. The average kinetic energy of the particles in a gas is directly proportional to the absolute temperature (in kelvin).

Deviation from ideal behaviour

Occurs at high pressures and low temperatures.

Avogadro's law

Equal volumes of gases at the same temperature and pressure will contain the same number of gas particles.

Ideal gas equation

PV = nRT.

Momentum

The product of an object's mass and its velocity.

Open system

A system that can exchange thermal energy (heat), work and matter (mass) with its surroundings.

Closed system

A system that can exchange thermal energy or work with its surroundings, but not matter.

Isolated system

A system that cannot exchange thermal energy, work or matter with its surroundings.

Positive value of work (W)

Work is done by the gas by expanding and pushing the piston upwards.

Negative value of work (W)

Work is done on the gas by compressing and pushing the piston downwards.

First law of thermodynamics

The thermal energy entering a closed system is equal to the sum of the change in internal energy of the system and the work done by the system.

Positive value of change in internal energy (∆U)

Increase in internal energy of the system.

Negative value of change in internal energy (∆U)

Decrease in internal energy of the system.

Positive value of energy (Q)

Thermal energy supplied to the system.

Negative value of energy (Q)

Thermal energy removed from the system.

Isothermal process

Temperature is constant (∆U = 0).

Isovolumetric process

Volume is constant (W = P∆V = 0).

Isobaric process

Constant pressure (Q=∆U+W).

Adiabatic process

No thermal energy is transferred between the system and surroundings (Q=0).

Adiabatic expansion

The temperature of a gas decreases (positive work negative internal energy).

Adiabatic compression

The temperature of a gas increases (negative work positive internal energy).

Isothermal line

Line on a PV diagram joining points with the same temperature.

Entropy

A measure of the amount of disorder of the particles in a system (number of possible microstates).

Microstate

A specific molecular configuration. It refers to all the permutations when we consider probability.

Macrostate

A measurable outcome, resulting from the outcome of each of the microstates. It refers to all the combinations when we consider probability.

Second law of thermodynamics

Thermal energy cannot spontaneously be transferred from a cold body to a hot body. In a cyclic process, it is impossible to completely convert heat into work.

Heat engine

A system that can produce work through cycles of thermodynamic processes, which can be repeated by returning the gas to its initial state.

Carnot cycle

An idealised theoretical thermodynamic cycle that involves four processes (adiabatic and isothermal), and the whole cycle is reversible. It has the theoretical maximum efficiency of any heat engine operating between two given temperatures.

Electrical insulator

A material in which charge carriers cannot flow easily.

Electrical conductors

A material in which charge carriers can flow easily.

Electromotive force

The work done per unit charge in moving charge across the terminals of a cell. It is the amount of energy that a source of energy, such as a cell, transfers to each unit of charge.

Electrical potential difference

The work done per unit charge on moving a positive charge between two points along the path of the current.

Electric current

The rate of flow of charge carriers.

Conventional current

The direction of flow of positive charges in a circuit.

Resistance

A measure of how difficult current can pass through an electrical component. It is harder for a current to pass through a component with high resistance than one with low resistance.

Resistivity

The property of a material that measures how strongly it resists current.

Ohm's Law

The electric potential difference across a conductor is directly proportional to the current flowing through it, at constant temperature.

Ohmic conductors

The electric potential difference across it per unit current (resistance) is constant.

Non-ohmic conductors

The electric potential difference across it per unit current (resistance) is not constant.

Thermistor

A thermistor is a type of temperature-sensitive resistor whose resistance increases as temperature decreases.

Light-dependent resistor (LDR)

When light intensity on the resistor increases, its resistance decreases.

Series circuit

All the components are in one loop of wire, and the same current flows through them all.

Parallel circuits

When components are connected in parallel, the circuit has different branches for the current to go through.

Voltmeter

A voltmeter measures electric potential difference (voltage) across a component.

Ammeter

An ammeter measures the rate of flow of charge carriers (electric current).

Specifications of Ideal ammeter

Zero resistance

Specifications of Ideal voltmeter

Infinite resistance

Electrical power

The rate of transfer of electrical energy.

Internal resistance

The resistance inside a cell that causes the electric potential difference across a cell to be less than its emf when the cell is in series with a resistor.

Potentiometer

A type of variable resistor that adjusts resistance by sliding a contact along a resistive track, allowing controlled voltage division in a circuit.

How is a voltmeter connected in a circuit?

A voltmeter is connected in parallel with the component it is measuring.

How is an ammeter connected in a circuit?

An ammeter is connected in series with the component it is measuring.

Why must an ammeter have minimal resistance?

To avoid causing a significant voltage drop, which would affect the measurement of current.

Why must a voltmeter have a high resistance?

To minimize the current it draws, preventing it from affecting the circuit.

Greenhouse Effect

Most of the electromagnetic radiation absorbed by the Earth is in the visible light region of the spectrum. This radiation is then re-emitted as infrared  radiation. Infrared is absorbed by the greenhouse gases  in the Earth’s atmosphere. The greenhouse gas particles in the atmosphere re-emit this energy in all directions. Some of the energy is re-emitted out to space and some is re-emitted back towards the Earth, thus trapping the energy in the Earth surface–atmosphere system.