A certain star has a temperature twice that of the Sun and a luminosity 64 times greater than the solar value. What is its radius, in solar units?

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### Problem Statement:

A certain star has a temperature twice that of the Sun and a luminosity 64 times greater than the solar value. What is its radius, in solar units?

### Explanation:

In this problem, we are given:
- The temperature of the star is twice that of the Sun, denoted as \( T = 2T_{\odot} \),
- The luminosity of the star is 64 times the luminosity of the Sun, denoted as \( L = 64L_{\odot} \).

We need to find the radius of the star in solar units (i.e., in terms of the Sun's radius).

### Key Formula to Use:

The relationship between luminosity, radius, and temperature of a star is given by the Stefan–Boltzmann law:

\[ L = 4\pi R^2 \sigma T^4 \]

where:
- \( L \) is the luminosity,
- \( R \) is the radius,
- \( T \) is the temperature,
- \( \sigma \) is the Stefan–Boltzmann constant.

For simplicity when comparing to the Sun, we can use ratios:

\[ \frac{L}{L_{\odot}} = \left( \frac{R}{R_{\odot}} \right)^2 \left( \frac{T}{T_{\odot}} \right)^4 \]

Substituting the given values:

\[ 64 = \left( \frac{R}{R_{\odot}} \right)^2 \left( 2 \right)^4 \]

\[ 64 = \left( \frac{R}{R_{\odot}} \right)^2 \times 16 \]

To isolate \( \left( \frac{R}{R_{\odot}} \right)^2 \):

\[ \left( \frac{R}{R_{\odot}} \right)^2 = \frac{64}{16} \]

\[ \left( \frac{R}{R_{\odot}} \right)^2 = 4 \]

Taking the square root of both sides:

\[ \frac{R}{R_{\odot}} = 2 \]

### Conclusion:

The radius of the star is 2 solar units. This means the star's radius is twice that of the Sun.
Transcribed Image Text:### Problem Statement: A certain star has a temperature twice that of the Sun and a luminosity 64 times greater than the solar value. What is its radius, in solar units? ### Explanation: In this problem, we are given: - The temperature of the star is twice that of the Sun, denoted as \( T = 2T_{\odot} \), - The luminosity of the star is 64 times the luminosity of the Sun, denoted as \( L = 64L_{\odot} \). We need to find the radius of the star in solar units (i.e., in terms of the Sun's radius). ### Key Formula to Use: The relationship between luminosity, radius, and temperature of a star is given by the Stefan–Boltzmann law: \[ L = 4\pi R^2 \sigma T^4 \] where: - \( L \) is the luminosity, - \( R \) is the radius, - \( T \) is the temperature, - \( \sigma \) is the Stefan–Boltzmann constant. For simplicity when comparing to the Sun, we can use ratios: \[ \frac{L}{L_{\odot}} = \left( \frac{R}{R_{\odot}} \right)^2 \left( \frac{T}{T_{\odot}} \right)^4 \] Substituting the given values: \[ 64 = \left( \frac{R}{R_{\odot}} \right)^2 \left( 2 \right)^4 \] \[ 64 = \left( \frac{R}{R_{\odot}} \right)^2 \times 16 \] To isolate \( \left( \frac{R}{R_{\odot}} \right)^2 \): \[ \left( \frac{R}{R_{\odot}} \right)^2 = \frac{64}{16} \] \[ \left( \frac{R}{R_{\odot}} \right)^2 = 4 \] Taking the square root of both sides: \[ \frac{R}{R_{\odot}} = 2 \] ### Conclusion: The radius of the star is 2 solar units. This means the star's radius is twice that of the Sun.
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