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3 years ago

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Quando aquecemos água em nossas casas, ao nível do mar, utilizando um recipiente aberto, sua temperatura nunca ultrapassa os 100

°C. Isso ocorre porque:
a) ao atingir essa temperatura, a agua perde sua capacidade de absorver calor.
b) ao atingir essa temperatura, a agua passa a perder exatamente a mesma quantidade de calor que esta recebendo, mantendo assim a temperatura constante.
c) as mudanças de fase ocorrem à temperatura constante.
d) ao atingir essa temperatura, a agua começa a expelir o oxigenio e outros gases nela dissolvidos.
e) as mudanças de fases de agua sempre ocorrem em 100 graus Celsius

1 answer:

iren2701 [21]3 years ago

4 0

Answer:

i dont speak spanish

Explanation:

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A circular loop of wire with a radius of 12.0 cm and oriented in the horizontal xy-plane is located in a region of uniform magne

Ulleksa [173]

(a) 34 V

The average emf induced in the loop is given by Faraday-Newmann-Lenz law:

$\epsilon = -\frac{\Delta \Phi_B}{\Delta t}$ (1)

where

$\Delta \Phi_B$ is the variation of magnetic flux through the coil

$\Delta t = 2.0 ms = 0.002 s$ is the time interval

We need to find the magnetic flux before and after. The magnetic flux is given by:

$\Phi_B = BA$

where

B is the magnetic field intensity

A is the area of the coil

The radius of the coil is r = 12.0 cm = 0.12 m, so its area is

$A=\pi r^2 = \pi (0.12 m)^2 = 0.045 m^2$

At the beginning, the magnetic field is

$B_i = 1.5 T$

so the flux is

$\Phi_i = B_i A = (1.5 T)(0.045 m^2)=0.068 Wb$

while after the removal of the coil, the magnetic field is zero, so the flux is also zero:

$\Phi_f = 0$

so the variation of magnetic flux is

$\Delta \Phi = 0-0.068 Wb=-0.068 Wb$

And substituting into (1) we find the average emf in the coil

$\epsilon=-\frac{-0.068 Wb}{0.002 s}=34 V$

(b) Counterclockwise

In order to understand the direction of the induced current, we have to keep in mind the negative sign in Lenz's law (1), which tells that the direction of the induced current must be such that the magnetic field produced by this current opposes the variation of magnetic flux in the coil.

In this situation, the magnetic flux through the coil is decreasing, since the coil is removed from the field. So, the induced current must be such that it produces a magnetic field whose direction is the same as the direction of the external magnetic field, which is upward along the positive z-direction.

Looking down from above and using the right-hand rule on the loop (thumb: direction of the current, other fingers wrapped: direction of magnetic field), we see that in order to produce at the center of the coil a magnetic field which is along positive z-direction, the induced current must be counterclockwise.

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3 years ago

A copper rod has a length of 1.3 m and a cross-sectional area of 3.6 10-4 m2. One end of the rod is in contact with boiling wate

sdas [7]

To solve the problem it is necessary to apply the concepts related to heat flow,

The heat flux can be defined as

$\frac{dQ}{dt} = H = \frac{kA\Delta T}{d}$

Where,

k = Thermal conductivity

A = Area of cross-sectional area

d = Length of the rod

$\Delta T=$ Temperature difference between the ends of the rod

$k =388 W/m.\°C$ Thermal conductivity of copper rod

$A = 3.6 *10^{-4} m$ Area of cross section of rod

$\Delta T=100-0=100\°C$ Temperature difference

$d=1.3m$ length of rod

Replacing then,

$H = \frac{kA\Delta T}{d}$

$H = \frac{(388)(3.6 *10^{-4})(100)}{1.3}$

$H=10.7446J$

From the definition of heat flow we know that this is also equivalent

$H = \dot{m}*L$

Where,

$\dot{m} =$ Mass per second

$L = 334J/g$ Latent heat of fusion of ice

Re-arrange to find $\dot{m},$

$H = \dot{m}*L$

$\dot{m}=\frac{L}{H}$

$\dot{m}=\frac{334}{10.7446}$

$\dot{m} = 31.08g/s$

$\dot{m}= 0.032g/s$

Therefore the mass of ice per second that melts is 0.032g

7 0

3 years ago

A car is designed to get its energy from a rotating

nydimaria [60]

Answer:

(a). The kinetic energy stored in the fly wheel is 46.88 MJ.

(b). The time is 1.163 hours.

Explanation:

Given that,

Radius = 1.50 m

Mass = 475 kg

Power $P= 15.0 hp = 15.0\times746=11190 watt$

Rotational speed = 4000 rev/min

We need to calculate the moment of inertia

Using formula of moment of inertia

$I=\dfrac{1}{2}mr^2$

Put the value into the formula

$I=\dfrac{1}{2}\times475\times(1.50)^2$

$I=534.375\ kg m^2$

(a). We need to calculate the kinetic energy stored in the fly wheel

Using formula of K.E

$K.E=\dfrac{1}{2}I\omega^2$

Put the value into the formula

$K.E = \dfrac{1}{2}\times534.375\times(4000\times\dfrac{2\pi}{60})^2$

$K.E=46880620.9\ J$

$K.E =46.88\times10^{6}\ J$

$K.E =46.88\ MJ$

(b). We need to calculate the length of time the car could run before the flywheel would have to be brought backup to speed

Using formula of time

$t=\dfrac{46.88\times10^{6}}{11190}$

$t=4189.45\ sec$

$t=1.163\ hours$

Hence, (a). The kinetic energy stored in the fly wheel is 46.88 MJ.

(b). The time is 1.163 hours.

3 0

3 years ago

Discuss the phase change condition due to reflection of light from a surface. Summarize equations of interference for thin film.

Dmitrij [34]

Answer:

if this surface has a higher index than in the medium where the light travels, the reflected wave has a phase change of 180º

Explanation:

When a ray of light falls on a surface if this surface has a higher index than in the medium where the light travels, the reflected wave has a phase change of 180º this can be explained by Newton's third law, the light when arriving pushes the atoms of the medium that is more dense, and these atoms respond with a force of equal magnitude, but in the opposite direction.

When the fractional index is lower than that of the medium where the reflacted beam travels, notice a change in phase.

Also, when light penetrates the medium, it modifies its wavelength

λ = λ₀ / n

We take these two aspects into account, the condition for contributory interference is

d sin θ = (m + 1/2) λ

for destructive interference we have

d sin θ = m λ

in general this phenomenon is observed at 90º

2 d = (m +1/2) λ° / n

2nd = (m + ½) λ₀

5 0

3 years ago

What is in the crysphere

butalik [34]

I think you mean the Cryosphere?

But the answer is D- Earths Ice

This word Cryosphere comes from the greek word "kryos" which means cold

Many people think of the cryosphere as being the north and south poles but snow and ice can be found in a lot of places on the Earth

3 0

3 years ago