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A 75,000-watt radio station transmits at 88 MHz. Determine the number of joules transmitted per second. 88 J/s 8800 J/s 2,000,00

Free_Kalibri [48]

Answer:

the first one is the correct answer

6 0

1 year ago

A body which has surface area 5cm² and temperature of 727°C radiates 300J of energy in one minute. Calculate it's emissivity giv

cestrela7 [59]

<h2>Answer: 0.17</h2>

Explanation:

The Stefan-Boltzmann law establishes that a black body (an ideal body that absorbs or emits all the radiation that incides on it) "emits thermal radiation with a total hemispheric emissive power proportional to the fourth power of its temperature":

$P=\sigma A T^{4}$ (1)

Where:

$P=300J/min=5J/s=5W$ is the energy radiated by a blackbody radiator per second, per unit area (in Watts). Knowing $1W=\frac{1Joule}{second}=1\frac{J}{s}$

$\sigma=5.6703(10)^{-8}\frac{W}{m^{2} K^{4}}$ is the Stefan-Boltzmann's constant.

$A=5cm^{2}=0.0005m^{2}$ is the Surface area of the body

$T=727\°C=1000.15K$ is the effective temperature of the body (its surface absolute temperature) in Kelvin.

However, there is no ideal black body (ideal radiator) although the radiation of stars like our Sun is quite close. So, in the case of this body, we will use the Stefan-Boltzmann law for real radiator bodies:

$P=\sigma A \epsilon T^{4}$ (2)

Where $\epsilon$ is the body's emissivity

(the value we want to find)

Isolating $\epsilon$ from (2):

$\epsilon=\frac{P}{\sigma A T^{4}}$ (3)

Solving:

$\epsilon=\frac{5W}{(5.6703(10)^{-8}\frac{W}{m^{2} K^{4}})(0.0005m^{2})(1000.15K)^{4}}$ (4)

Finally:

$\epsilon=0.17$ (5) This is the body's emissivity

3 0

2 years ago

What's the frequency of a wave with a wavelength of 10 and velocity of 200m/s?

uranmaximum [27]

Answer:

$\boxed {\boxed {\sf 20 \ Hz}}$

Explanation:

The frequency of a wave can be found using the following formula.

$f=\frac{v}{\lambda}$

where f is the frequency, v is the velocity/wave speed, and λ is the wavelength.

The wavelength is 10 meters and the velocity is 200 meters per second.

1 m/s can also be written as 1 m*s^-1

Therefore:

$v= 200 \ m*s^{-1} \\\lambda = 10 \ m$

Substitute the values into the formula.

$f=\frac{200 \ m*s^{-1}}{10 \ m}$

Divide and note that the meters (m) will cancel each other out.

$f=\frac{200 \ s^{-1}}{10 \ }$

$f=20 \ s^{-1}$

1 s^-1 is equal to Hertz
Therefore, our answer of 20 s^-1 is equal to 20 Hz

$f= 20 \ Hz$

The frequency of the wave is 20 Hertz

7 0

2 years ago

What force is required to accelerate a 385 kg couch at 0.2 m/s^2 ?

Juliette [100K]

Answer:

It takes 77 N

Explanation:

Using Newton's second law of motion, F=ma (Force equals mass times acceleration. Since the mass of the couch is 385 kg and the target acceleration is 0.2 m/s, you simply multiply mass times acceleration (ma) to get the total force, or 77 N.

6 0

2 years ago

3. Electrons are the only part of an atom that can be transferred between materials. True or

meriva

False

Explanation:

The electrons cloud patterns are extremely complex and is of no importance to the discussion of electric charge in the atom. More important is the fact that electrons are labile; that is, they can be transferred from one atom to the next. It is through electronic transfer that atoms become charged.

6 0

2 years ago

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