The intensity of a sunspot is found to be 3 times smaller than the intensity emitted by the solar surface. what is the approximate temperature of this sunspot if the temperature of the solar surfaceis 5800 k?
a. 4400 k
b. 470,000 k
c. 1900 k
d. 7600 k
e. 1400 k

If the temperature of the solar surface is 5800 K then the approximate temperature of the sunspot is a) 4400 K.

Explanation:

The most straightforward way to solve this is using Stefan-Boltzmann law that states that I the energy radiated per unit surface area per unit time (watt per unit area ) of a black body is proportional to the fourth power of the temperature T of the body:

with being the Stefan constant.

A black body is an idealized physical body that is a perfect absorber because it absorbs all incident electromagnetic radiation and is also an ideal emitter. The Sun is considered to be a black body at different layers and different temperatures.

We are told that the intensity of a sunspot is found to be 3 times smaller than the intensity emitted by the solar surface , that means that:

then using the expression of Stefan-Boltzmann law we get that

we cross out and use the fourth root in each side of the equation

then we use that

So finally we get that

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.