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ipn [44]
3 years ago
15

Recall from Chapter 1 that a watt is a unit of en- ergy per unit time, and one watt (W) is equal to one joule per second ( J·s–1

). A 100-W incandescent light- bulb produces about 4% of its energy as visible light. Assuming that the light has an average wavelength of 510 nm, calculate how many such photons are emit- ted per second by a 100-W incandescent lightbulb.
Physics
1 answer:
harkovskaia [24]3 years ago
3 0

Answer:

Explanation:

The energy of a photon is given by the equation E_p=h f, where h is the <em>Planck constant</em> and f the frequency of the photon. Thus, N photons of frequency f will give an energy of E_N=N h f.

We also know that frequency and wavelength are related by f=\frac{c}{\lambda}, so we have E_N=\frac{N h c}{\lambda}, where c is the <em>speed of light</em>.

We will want the number of photons, so we can write

N=\frac{\lambda E_N}{h c}

We need to know then how much energy do we have to calculate N. The equation of power is P=E/t, so for the power we have and considering 1 second we can calculate the total energy, and then only consider the 4% of it which will produce light, or better said, the N photons, which means it will be E_N.

Putting this paragraph in equations:

E_N=(\frac{4}{100})E=0.04Pt=(0.04)(100W)(1s)=4J.

And then we can substitute everything in our equation for number of photons, in S.I. and getting the values of constants from tables:

N=\frac{\lambda E_N}{h c}=\frac{(520 \times10^{-9}m) (4J)}{(6.626\times10^{-34}Js) (299792458m/s)}=1.047 \times10^{19}

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A wave is 8 meters long and has a frequency of 3 Hz. Find speed
Olenka [21]

Answer:

The speed is 24 \frac{meter}{s}

Explanation:

A wave is a disturbance that propagates through a certain medium or in a vacuum, with transport of energy but without transport of matter.

The wavelength is the minimum distance between two successive points of the wave that are in the same state of vibration. It is expressed in units of length (m).

Frequency is the number of vibrations that occur in a unit of time. Its unit is s⁻¹ or hertz (Hz).

The speed of propagation is the speed with which the wave propagates in the middle, that is, the magnitude that measures the speed at which the wave disturbance propagates along its displacement. Relate wavelength (λ) and frequency (f) inversely proportionally using the following equation:

v = f * λ.

In this case, λ= 8 meter and f= 3 Hz

Then:

v= 3 Hz* 8 meter

So:

v= 24 \frac{meter}{s}

<u><em>The speed is 24 </em></u>\frac{meter}{s}<u><em></em></u>

5 0
3 years ago
If a 1 kg book has 46 Joules of gravitational potential energy how high is the shelf it is on?
Mashcka [7]

Answer:

4.7m

Explanation:

Given parameters:

Mass of the book  = 1kg

Gravitational potential energy  = 46J

Unknown:

Height of the shelf  = ?

Solution:

The potential energy is due to the position of a body above the ground.

        Gravitational potential energy  = mgh

m is the mass,

g is the acceleration due gravity  = 9.8m/s²

h is the height which is unknown

                       46  = 1 x 9.8 x h

                       h  = 4.7m

4 0
3 years ago
Suppose a log's mass is 5 kg. After burning, the mass of the ash is 1 kg. explain what May have happened to the other 4 kg.
ladessa [460]

The other 4 kg of mass may have departed the scene
of the fire, in the form of gases and smoke particles.

7 0
3 years ago
An object with height h, mass M, and a uniform cross-sectional area A floats upright in a liquid with density ρ.
soldi70 [24.7K]
** Missing information: The vertical distance from surface of liquid to bottom of the object is sought in this question, with the condition that the object is at equilibrium **

Ans: The vertical distance = y = M/(ρA)

Explanation:

Support the vertical distance = y

Object's density = M/(A*h) (since A*h = volume)

By applying the condition, 

(M/(Ah))/ρ = y/h

M/(ρAh) = y/h

y = M/(ρA)  

7 0
4 years ago
The power of the kettle was 2.6 kW
faltersainse [42]

Answer:

Cp = 4756 [J/kg*°C]

Explanation:

In order to calculate the specific heat of water, we must use the equation of energy for heat or heat transfer equation.

Q = m*Cp*(T_f - T_i)/t

where:

Q = heat transfer = 2.6 [kW] = 2600[W]

m = mass of the water = 0.8 [kg]

Cp = specific heat of water [J/kg*°C]

T_f  = final temperature of the water = 100 [°C]

T_i = initial temperature of the water = 18 [°C]

t = time = 120 [s]

Now clearing the Cp, we have:

Cp = Q*t/(m*(T_f - T_i))

Now replacing

Cp = (2600*120)/(0.8*(100-18))

Cp = 4756 [J/kg*°C]

7 0
3 years ago
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