Suppose an isotropic light source has a power of 59 W and that its light is normally incident on a partially-reflecting surface at a distance of 2.69 m from the source. Calculate the average radiation pressure (in nPa) if the surface reflects 51% of the incident light. (Use c = 2.9979 x 108 m/s)

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**Problem Statement:**

Suppose an isotropic light source has a power of 59 W and that its light is normally incident on a partially-reflecting surface at a distance of 2.69 m from the source. Calculate the average radiation pressure (in nPa) if the surface reflects 51% of the incident light. (Use \( c = 2.9979 \times 10^8 \) m/s)

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**Explanation of Concepts:**

1. **Isotropic Light Source:** An isotropic light source emits light uniformly in all directions.

2. **Power:** The power of the light source is given as 59 Watts, which is the rate at which energy is emitted from the source.

3. **Radiation Pressure:** This is the pressure exerted by electromagnetic radiation on a surface. It depends on the intensity of the light and the reflectivity of the surface.

4. **Reflectivity:** In this scenario, the surface reflects 51% of the incident light.

5. **Speed of Light:** The speed of light (\( c \)) is provided as \( 2.9979 \times 10^8 \) m/s, which is crucial for calculating the radiation pressure.

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**Solution Approach:**

To solve for the average radiation pressure, use the formula for radiation pressure on a reflecting surface:

\[ P = \frac{2I}{c} \times \text{Reflectivity} \]

Where:
- \( P \) is the radiation pressure.
- \( I \) is the intensity of the light, calculated as \( \frac{\text{Power}}{\text{Area}} \).
- \( c \) is the speed of light.
- Reflectivity is the fraction of light that is reflected.

1. **Calculate Intensity (I):**

The intensity \( I \) at a distance \( r \) from an isotropic source:

\[
I = \frac{P_{\text{source}}}{4\pi r^2}
\]

2. **Calculate Radiation Pressure (P):**

\[
P = \frac{2I}{c} \times \text{Reflectivity}
\]

By plugging in the given values, you can determine the radiation pressure in nanopascals (nPa). 

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Transcribed Image Text:**Problem Statement:** Suppose an isotropic light source has a power of 59 W and that its light is normally incident on a partially-reflecting surface at a distance of 2.69 m from the source. Calculate the average radiation pressure (in nPa) if the surface reflects 51% of the incident light. (Use \( c = 2.9979 \times 10^8 \) m/s) --- **Explanation of Concepts:** 1. **Isotropic Light Source:** An isotropic light source emits light uniformly in all directions. 2. **Power:** The power of the light source is given as 59 Watts, which is the rate at which energy is emitted from the source. 3. **Radiation Pressure:** This is the pressure exerted by electromagnetic radiation on a surface. It depends on the intensity of the light and the reflectivity of the surface. 4. **Reflectivity:** In this scenario, the surface reflects 51% of the incident light. 5. **Speed of Light:** The speed of light (\( c \)) is provided as \( 2.9979 \times 10^8 \) m/s, which is crucial for calculating the radiation pressure. --- **Solution Approach:** To solve for the average radiation pressure, use the formula for radiation pressure on a reflecting surface: \[ P = \frac{2I}{c} \times \text{Reflectivity} \] Where: - \( P \) is the radiation pressure. - \( I \) is the intensity of the light, calculated as \( \frac{\text{Power}}{\text{Area}} \). - \( c \) is the speed of light. - Reflectivity is the fraction of light that is reflected. 1. **Calculate Intensity (I):** The intensity \( I \) at a distance \( r \) from an isotropic source: \[ I = \frac{P_{\text{source}}}{4\pi r^2} \] 2. **Calculate Radiation Pressure (P):** \[ P = \frac{2I}{c} \times \text{Reflectivity} \] By plugging in the given values, you can determine the radiation pressure in nanopascals (nPa). ---
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