physics B.1 and B.2
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77 Terms
What are the three states of matter?
Solid, liquid, and gas.
How are particles arranged in a solid?
They are closely packed in a fixed, regular arrangement.
How do particles move in a solid?
They vibrate around fixed positions.
Why does a solid have a fixed shape and volume?
Strong intermolecular forces keep its particles in fixed positions.
How are particles arranged in a liquid?
They are close together but not fixed in position.
How do particles move in a liquid?
They slide past one another.
Why does a liquid have a fixed volume but no fixed shape?
Its particles stay close together but can move around each other.
How are particles arranged in a gas?
They are far apart with lots of empty space between them.
How do gas particles move?
They move freely and rapidly in random directions.
Why are gases highly compressible?
There is a large amount of empty space between gas particles.
What happens to molecular motion as temperature increases?
Molecular motion generally increases.
What happens to intermolecular forces as matter changes from solid to liquid to gas?
Their influence becomes weaker.
What does temperature measure at the particle level?
The average kinetic energy of particles.
Does a temperature change of 1°C equal a change of 1 K?
Yes, temperature changes have the same size in Celsius and Kelvin.
What is internal energy?
The total microscopic kinetic and potential energy of the particles in a substance.
What contributes to the kinetic part of internal energy?
The random motion of particles.
What contributes to the potential part of internal energy?
Interactions and forces between particles.
Does temperature always equal internal energy?
No. Objects at the same temperature can have different internal energies.
Temperature and internal energy are fundamentally different physical quantities: temperature measures the average kinetic energy per particle (an intensive property), while internal energy is the total energy of all particles in a system, combining both kinetic and potential energy (an extensive property). [1, 2, 3]
They do not equal each other for several key reasons:
1. Intensive vs. Extensive Properties
Temperature is intensive: It does not depend on how much matter you have. A single drop of boiling water and a full pot of boiling water have the exact same temperature (\(100^{\circ }\text{C}\)). [1, 2]
Internal energy is extensive: It scales with the amount of substance present. The full pot of boiling water contains vastly more molecules than a single drop, meaning its total internal energy is much higher. For example, a warm bathtub of water has the same temperature as a small cup of warm water, but the bathtub has far more internal energy because of its massive particle count. [1, 2, 3, 4]
What mainly changes when temperature rises without a phase change?
The average kinetic energy of the particles increases.
What mainly changes during a phase change?
The potential energy associated with particle interactions changes.
Why does temperature stay constant during a phase change?
Energy is used to change particle spacing and interactions instead of increasing kinetic energy.
What happens during melting?
A solid changes into a liquid.
What happens during freezing?
A liquid changes into a solid.
What happens during boiling?
A liquid changes into a gas.
What happens during condensation?
A gas changes into a liquid.
Does adding energy during melting immediately raise temperature?
No. The energy is used to overcome intermolecular forces.
Does removing energy during freezing immediately lower temperature?
Not during the phase change; energy is released as stronger interactions form.
Why does vaporization generally require more energy than melting?
Separating particles into a gas requires overcoming more intermolecular attraction.
What is conduction?
Thermal energy transfer through particle collisions or free electrons.
Where is conduction especially important?
In solids, especially metals.
Why are metals good thermal conductors?
Free electrons can transfer energy rapidly through the material.
What factors affect the rate of conduction?
Material, temperature difference, area, and thickness.
What is convection?
Thermal energy transfer by the bulk movement of a fluid.
In which states of matter does convection occur?
Liquids and gases.
Why does warm fluid rise?
It becomes less dense than the surrounding cooler fluid.
Why does cool fluid sink?
It is denser than warmer fluid around it.
What is a convection current?
A circulating movement caused by warm fluid rising and cool fluid sinking.
Why can convection not occur in solids?
Solid particles cannot flow in bulk.
What is thermal radiation?
Energy transferred by electromagnetic waves.
Does thermal radiation require matter to travel through?
No. It can travel through a vacuum.
Why is radiation important for energy transfer through space?
Space is mostly a vacuum, so conduction and convection cannot transfer energy through it effectively.
What is a black body?
An ideal object that absorbs all incident radiation and emits the maximum possible radiation at its temperature.
What is luminosity?
The total power emitted by an object.
What is apparent brightness?
The power received per unit area by an observer.
Does luminosity depend on how far away an observer is?
No. Luminosity is an intrinsic property of the source.
Does apparent brightness depend on distance?
Yes. It decreases as distance from the source increases.
What happens to apparent brightness when distance increases?
The object appears dimmer because its energy spreads over a larger area.
What does Wien’s law tell us conceptually?
Hotter objects emit most strongly at shorter wavelengths.
How can the temperature of a star be estimated from its spectrum?
Find the wavelength where its emitted radiation is strongest.
How does the peak wavelength change as an object gets hotter?
It shifts to shorter wavelengths.
What is emissivity?
A measure of how effectively a real surface emits thermal radiation compared with a perfect black body.
What emissivity does a perfect black body have?
An emissivity of 1.
What does low emissivity mean?
The surface is a relatively poor emitter of thermal radiation.
What is albedo?
The fraction of incoming radiation reflected by a surface.
What does a high albedo surface do?
It reflects a large fraction of incoming radiation.
What does a low albedo surface do?
It absorbs a larger fraction of incoming radiation.
Give an example of a high albedo surface.
Snow or ice.
Give an example of a low albedo surface.
Forests or other dark surfaces.
How does high albedo affect surface temperature?
More radiation is reflected, so less energy is absorbed.
How does low albedo affect surface temperature?
More radiation is absorbed, which can increase warming.
What is the solar constant?
The intensity of sunlight reaching the top of Earth's atmosphere at Earth's distance from the Sun.
Why is Earth's average incoming solar intensity lower than the solar constant?
Sunlight is spread over Earth's entire spherical surface.
Why is the actual energy absorbed by Earth lower than the incoming solar energy?
Some energy is reflected or scattered by clouds, the atmosphere, and Earth's surface.
What are the main greenhouse gases listed in these notes?
Carbon dioxide, methane, water vapor, and nitrous oxide.
Are greenhouse gases mostly transparent to incoming sunlight?
Yes. They allow much of the incoming short-wave radiation to pass through.
What type of radiation do greenhouse gases strongly absorb?
Outgoing long-wave infrared radiation.
Why can greenhouse gas molecules absorb infrared radiation?
Their molecular vibrations and rotations interact with infrared wavelengths.
What happens after a greenhouse gas absorbs infrared radiation?
It re-emits infrared radiation in different directions.
How does re-emitted infrared radiation warm Earth?
Some is directed back toward the surface, reducing the rate at which energy escapes to space.
Why are nitrogen and oxygen not major greenhouse gases?
Their molecules do not absorb infrared radiation effectively because their vibrations do not create a changing dipole.
What is the natural greenhouse effect?
The natural warming of Earth caused by greenhouse gases absorbing and re-emitting infrared radiation.
Why is the natural greenhouse effect important?
It keeps Earth warm enough for conditions suitable for life.
What is the enhanced greenhouse effect?
Additional warming caused by increased greenhouse gas concentrations from human activities.
What happens when greenhouse gas concentration increases?
More outgoing infrared radiation is absorbed and re-emitted.
How can melting ice create a positive feedback loop?
Less ice lowers albedo, causing more absorption and warming, which melts even more ice.
Why does melting ice generally increase warming?
Darker surfaces are exposed, lowering albedo and increasing absorbed solar energy.
What determines Earth's overall temperature?
The balance between incoming solar radiation and outgoing thermal radiation.