- 1(current)
Q. No.If the sun’s surface radiates heat at \(6.3\times 10^{7}~\text{Wm}^{-2}\) then the temperature of the sun, assuming it to be a black body, will be:
\(\left(\sigma = 5.7\times 10^{-8}~\text{Wm}^{-2}\text{K}^{-4}\right)\)
1. \(5.8\times 10^{3}~\text{K}\)
2. \(8.5\times 10^{3}~\text{K}\)
3. \(3.5\times 10^{8}~\text{K}\)
4. \(5.3\times 10^{8}~\text{K}\)
| 1. | \(\left(\dfrac{\alpha}{\sigma \times 4 \pi R^2}\right)^{\dfrac{1}{4}}\) | 2. | \(\left(\dfrac{\sigma \times 4 \pi R^2}{\alpha}\right)^{\dfrac{1}{4}}\) |
| 3. | \(\left(\dfrac{\alpha}{\sigma \times 4 \pi R^2}\right)\) | 4. | \(\left(\dfrac{4 \pi R^2 \times \sigma}{\alpha}\right)\) |
| 1. | increases by a factor of \(4\) |
| 2. | increases by a factor of \(2\) |
| 3. | remains unchanged |
| 4. | decreases by a factor of \(2\) |
1. \(1:4\)
2. \(3:1\)
3. \(1:2\)
4. \(6:1\)
The total radiant energy per unit area, normal to the direction of incidence, received at a distance \(R\) from the centre of a star of radius \(r,\) whose outer surface radiates as a black body at a temperature \(T\) K is given by: (Where \(\sigma\) is Stefan’s constant):
1. \(\dfrac{\sigma r^{2}T^{4}}{R^{2}}\)
2. \(\dfrac{\sigma r^{2}T^{4}}{4 \pi R^{2}}\)
3. \(\dfrac{\sigma r^{2}T^{4}}{R^{4}}\)
4. \(\dfrac{4\pi\sigma r^{2}T^{4}}{R^{2}}\)
- 1(current)
Q. No.
© 2025 GoodEd Technologies Pvt. Ltd.