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bixtya [17]
3 years ago
9

Estimate the number of photons emitted per second from 1.0 cm2 of a person's skin if a typical emitted photon has a wavelength o

f 10,000 nm. Assume the skin of a person is at the normal body temperature of 37∘C.
Physics
1 answer:
Diano4ka-milaya [45]3 years ago
4 0

Answer:

2.63 x 10^18

Explanation:

A = 1 cm^2 = 1 x 10^-4 m^2

λ = 10,000 nm = 10,000 x 10^-9 m = 10^-5 m

T = 37 degree C = 37 + 273 = 310 k

Energy of each photon = h c / λ

where, h is the Plank's constant and c be the velocity of light

Energy of each photon = (6.63 x 10^-34 x 3 x 10^8) / 10^-5 = 1.989 x 10^-20 J

Energy radiated per unit time = σ A T^4

Where, σ is Stefan's constant

Energy radiated per unit time = 5.67 x 10^-8 x 10^-4 x 310^4 = 0.05236 J

Number of photons per second = Energy radiated per unit time / Energy of  

                                                                                               each photon

Number of photons per second = 0.05236 / (1.989 x 10^-20) = 2.63 x 10^18

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What's the diameter of a dish antenna that will receive 10−20W of power from Voyager at this time? Assume that the radio transmi
Murrr4er [49]

Complete Question:

The Voyager 1 spacecraft is now beyond the outer reaches of our solar system, but earthbound scientists still receive data from the spacecraft s 20-W radio transmitter. Voyager is expected to continue transmitting until about 2025, when it will be some 25 billion km from Earth.

What s the diameter of a dish antenna that will receive 10−20W of power from Voyager at this time? Assume that the radio transmitter on Voyager transmits equally in all directions(isotropically).  In fact, the antenna on Voyager focuses the signal in a beam aimed at the earth, so this problem over-estimates the size of the receiving dish needed.

Answer:

d = 2,236 m.

Explanation:

The received power on Earth, can be calculated as the product of the intensity (or power density) times the area that intercepts the power radiated.

As we assume that  the transmitter antenna is ominidirectional, power is spreading out over a sphere with a radius equal to the distance to the source.

So, we can get the power density as follows:

I = P /A = P / 4*π*r², where P = 20 W, and r= 25 billion km = 25*10¹² m.

⇒ I = 20 W / 4*π* (25*10¹²)² m²

The received power, is just the product of this value times the area of the receiver antenna, which we assumed be a circle of diameter d:

Pr = I. Ar =( 20W / 4*π*(25*10¹²)² m²) * π * (d²/4) = 10⁻²⁰ W

Simplifying common terms, we can solve for d:

d= √(16*(25)²*10⁴/20) = 2,236 m.

3 0
3 years ago
a coin press creates a pressure of 3.20*10^8 Pa on a nickel of radius 0.0106 m. how much force does the press exert on the coin?
Naya [18.7K]

Answer:

1.13 x 10⁵N

Explanation:

Given parameters:

Pressure of the coin press = 3.2 x 10⁸ Pa

radius of the nickel coin = 0.0106m

Unknown:

Force of the press on coil = ?

Solution:

Our knowledge of pressure will help us solve this problem.

Pressure is defined as the force applied per unit area on a body.

              Pressure  = \frac{force}{area}

  Force = Pressure  x  Area

 Since the pressure is known;

Area of the coin = Area of a circle = π r²

 where r is the radius of the coin;

Area of the coin = π x 0.0106²  = 3.53 x 10⁻⁴m²

  Force = 3.2 x 10⁸ x  3.53 x 10⁻⁴  = 1.13 x 10⁵N

3 0
3 years ago
What is amplitude?
nydimaria [60]
1. Frequency  is the number of complete waves that pass a point in a second.   2.Wavelength is the distance between two crests or two troughs.                     3.Time period <span> is the time it takes for one complete wave to pass a given point. 4. Amplitude is the height of the wave.   Hence option 4 is correct. </span>
8 0
3 years ago
Draw a schematic diagram of a circuit consisting of a battery of five 2 V cells, a 5 ohm resistor, a 10 ohm resistor, a 15 ohm r
MakcuM [25]

Answer:

  • Current = 0.33 A

Explanation:

  • For diagram refer the attachment.

It is given that five cells of 2V are connected in series, so total voltage of the battery:

\dashrightarrow \: \:  \sf V = 2 \times 5 = 10 V

Three resistor of 5\Omega, 10\Omega, 15\Omega are connected in Series, so the net resistance:

\dashrightarrow \: \: \sf R_{n} = R_{1} + R_{2} + R_{3}

\dashrightarrow \: \:  \sf R = 5 + 10 + 15

{ \pink{\dashrightarrow \sf \: \: { \underbrace{R = 30 \:  \Omega}}}}

According to ohm's law:

\dashrightarrow  \sf\: \: V = IR

\dashrightarrow  \sf \: \: I = \dfrac{V}{R}

On substituting resultant voltage (V) as 10 V and resultant resistant, as 30 {\pmb{\sf{\Omega}}} we get:

\dashrightarrow \sf \: \: I = \dfrac{10V}{30\Omega}

{ \pink{\dashrightarrow \sf \: \: { \underbrace{I = 0.33 A}}}}

\thereforeThe electric current passing through the above circuit when the key is closed will be <u>0.33 A</u>

4 0
2 years ago
Read 2 more answers
A student places her 490 g physics book on a frictionless table. She pushes the book against a spring, compressing the spring by
Paul [167]

Answer:

book speed is 3.99 m/s

Explanation:

given data

mass m = 490 g = 0.490 kg

compressing x = 7.10 cm = 0.0710 m

spring constant k = 1550 N/m

to find out

book speed

solution

we know energy is conserve so

we can say

loss in spring energy is equal to gain in kinetic energy

so

\frac{1}{2}*k*x^2 = \frac{1}{2}*m*v^2    ..................1

put here value

\frac{1}{2}*1550*0.071^2 = \frac{1}{2}*0.490*v^2

v = 3.99 m/s

so book speed is 3.99 m/s

5 0
3 years ago
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