IB Physics Topic B.2.1 Conservation of Energy in Earth’s Atmosphere Revision Notes (SL/HL)

IB Physics Topic B.2.1 Conservation of Energy in Earth’s Atmosphere Revision Notes (SL/HL) | RevisionDojo

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Emissivity: How Efficiently a Surface Radiates Energy

Definition

Emissivity

Emissivity ($e$) measures how efficiently a surface radiates energy compared to an ideal black body.

A black body is a perfect emitter with an emissivity of 1, meaning it radiates the maximum possible energy at a given temperature.
Real surfaces have emissivity values between 0 and 1.
The formula for emissivity is: $$e = \frac{\text{Power radiated per unit area}}{\sigma T^4}$$ where:
1. $e$ is the emissivity.
2. $\sigma$ is the Stefan-Boltzmann constant ($5.67 \times 10^{-8} \, \text{W m}^{-2} \, \text{K}^{-4}$).
3. $T$ is the absolute temperature of the surface in Kelvin.

How Emissivity Affects Radiation

High emissivity: Surfaces with emissivity close to 1, like black bodies, radiate energy efficiently.
Low emissivity: Surfaces with emissivity near 0, like polished metals, radiate much less energy.

Example

A surface with emissivity $e = 0.8$ radiates 80% of the energy a black body would at the same temperature.

Emissivity in the Real World

Different surfaces have varying emissivity values:

Oceans: High emissivity (~0.8), radiating energy efficiently.
Ice: High emissivity (~0.98), radiating energy efficiently.

Note

Emissivity depends on factors like material composition, surface texture, and temperature.

Albedo: How Much Energy is Reflected

Definition

Albedo

Albedo ($\alpha$) measures the reflectivity of a surface.

It is the fraction of incoming radiation that is reflected back into space.
The formula for albedo is: $$
\alpha = \frac{\text{Total scattered power}}{\text{Total incident power}}
$$

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Emissivity: How Efficiently a Surface Radiates Energy

Definition

Emissivity

Emissivity ($e$) measures how efficiently a surface radiates energy compared to an ideal black body.

A black body is a perfect emitter with an emissivity of 1, meaning it radiates the maximum possible energy at a given temperature.
Real surfaces have emissivity values between 0 and 1.
The formula for emissivity is: $$e = \frac{\text{Power radiated per unit area}}{\sigma T^4}$$ where:
1. $e$ is the emissivity.
2. $\sigma$ is the Stefan-Boltzmann constant ($5.67 \times 10^{-8} \, \text{W m}^{-2} \, \text{K}^{-4}$).
3. $T$ is the absolute temperature of the surface in Kelvin.

How Emissivity Affects Radiation

High emissivity: Surfaces with emissivity close to 1, like black bodies, radiate energy efficiently.
Low emissivity: Surfaces with emissivity near 0, like polished metals, radiate much less energy.

Example

A surface with emissivity $e = 0.8$ radiates 80% of the energy a black body would at the same temperature.

Emissivity in the Real World

Different surfaces have varying emissivity values:

Oceans: High emissivity (~0.8), radiating energy efficiently.
Ice: High emissivity (~0.98), radiating energy efficiently.

Note

Emissivity depends on factors like material composition, surface texture, and temperature.

Albedo: How Much Energy is Reflected

Definition

Albedo

Albedo ($\alpha$) measures the reflectivity of a surface.

It is the fraction of incoming radiation that is reflected back into space.
The formula for albedo is: $$
\alpha = \frac{\text{Total scattered power}}{\text{Total incident power}}
$$

Definition

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Topic A - Space, time and motion5 subtopics

Topic B - The particulate nature of matter5 subtopics

Topic C - Wave behaviour5 subtopics

Topic D - Fields4 subtopics

Topic E - Nuclear and quantum physics5 subtopics

IB Physics B.2.1 Conservation of Energy in Earth’s Atmosphere Notes

Topic A - Space, time and motion5 subtopics

Topic B - The particulate nature of matter5 subtopics

Topic C - Wave behaviour5 subtopics

Topic D - Fields4 subtopics

Topic E - Nuclear and quantum physics5 subtopics

Emissivity: How Efficiently a Surface Radiates Energy

How Emissivity Affects Radiation

Emissivity in the Real World

Albedo: How Much Energy is Reflected

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Duis aute irure dolor in reprehenderit

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Emissivity: How Efficiently a Surface Radiates Energy

How Emissivity Affects Radiation

Emissivity in the Real World

Albedo: How Much Energy is Reflected

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Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

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