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3 years ago

How do astronomers determine the surface temperature of stars? *

Physics

1 answer:

RideAnS [48]3 years ago

7 0

Answer:

To the extent that Stellar spectra look like blackbodies, the temperature of a star can also be measured amazingly accurately by recording the brightness in two different filters. To get a stellar temperature: Measure the brightness of a star through two filters and compare the ratio of red to blue light.

Explanation:

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The work done by a force is greatest when the force and the displacement vectors are ________.

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The answer is B . Parallel

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3 years ago

Jean- Baptiste Say argued that entrepreneurs should be called the fourth factor of production because they

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4 years ago

If an object has zero acceleration, does that mean it has zero velocity?

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3 years ago

Read 2 more answers

Your forehead can withstand a force of about 6.0 kn before fracturing, while your cheekbone can withstand only about 1.3 kn. sup

Vinil7 [7]

a) The change in momentum of the ball is given by:

$\Delta p = m \Delta v$

where m=140 g=0.14 kg is the mass of the ball, and $\Delta v =30 m/s$ is the change in velocity. Substituting, we find

$\Delta p=(0.14 kg)(30 m/s)=4.2 kg m/s$

The ball stops in t=1.5 ms=0.0015 s; the magnitude of the force that stops the baseball is given by the ratio between the change in momentum and the time taken:

$F=\frac{\Delta p}{t}=\frac{4.2 kg m/s}{0.0015 s}=2800 N=2.8 kN$

b) The force we found at point a) is the force that the head exerts on the ball to stop it. However, Newton's third law states that when an object A exerts a force on an object B, object B also exerts a force equal and opposite on object A. If we apply this law to this case, we understand that the force exerted by the baseball on the head is equal to the force exerted by the head on the ball: therefore, the answer is still 2.8 kN.

c) The forehead is not in danger of a fracture, since it can withstand a maximum force of 6.0 kN, while the ball exerts a force of 2.8 kN. Instead, the cheek is in danger of fracture, because it can withstand only a maximum force of 1.3 kN.

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3 years ago

Find the energy of one quantum of microwave radiation with frequency 4 GHz and with 500 GHz .

REY [17]

Answer:

1. $1.65*10^{-5} eV$ and $2.07*10^{-3}eV$ 2. $2.10*10^{-7}m$

Explanation:

The energy of a photon is given by the so-called Planck-Einstein relation:

$E=fh=\frac{ch}{\lambda}$

where E is the energy, f the frequency, $\lambda$ the wavelength, c the speed of light and h the planck constant

So, we have:

$E=fh\\E=(4*10^9Hz)(4.136*10^{-15}eV*s)=1.65*10^{-5} eV\\$

And:

$E=fh\\E=(5*10^{11}Hz)(4.136*10^{-15}eV*s)=2.07*10^{-3} eV\\$

2. The work function is the amount of energy required to remove an electron from the material. Therefore the kinetic energy of the photoelectrons will be the energy of the electromagnetic radiation minus the work function:

$K=E-W$

Where K is the kinetic energy and W the work function, for copper W=4.7eV

Rewriting for $\lambda$ :

$E=K+W\\\frac{ch}{\lambda}=K+W\\\lambda=\frac{ch}{K+W}\\\lambda=\frac{(3*10^8m/s)4.136*10^{-15}eV}{1.2eV+4.7eV}=2.10*10^{-7}m$

This wavelength corresponds to the ultraviolet range

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3 years ago