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3 years ago

How does incident light that falls on an object affect the motion of electrons in the atoms of the object?

Physics

1 answer:

KonstantinChe [14]3 years ago

5 0

Explanation:

Incident light makes an electron oscillate. The electrons emit light or absorb the light, collide with other electrons, thereby converting light energy to more internal energy. and convert it to heat.

Light wave of a given frequency is incident on a material with electrons having the same vibrational frequencies, then electrons absorb the energy of the light wave and transform it into vibrational motion.

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Determine the power that needs to besupplied by the fanifthe desired velocity is 0.05 m3/s and the cross-sectional area is 20 cm

Mariulka [41]

Answer:

A fan with an energy efficiency of 30 % would need 62.5 watts to bring a desired volume flow of 0.05 cubic meters per second through a cross-sectional area of 20 square centimeters.

Explanation:

Complete statement is: <em>Determine the power that needs to besupplied by the fan if the desired velocity is 0.05 cubic meters per second and the cross-sectional area is 20 square centimeters.</em>

From Thermodynamics and Fluid Mechanics we know that fans are devices that work at steady state which accelerate gases (i.e. air) with no changes in pressure. In this case, mechanical rotation energy is transformed into kinetic energy. If we include losses due to mechanical friction, the Principle of Energy Conservation presents the following equation:

$\eta\cdot \dot W = \dot K$

$\dot W = \frac{\dot K}{\eta}$ (Eq. 1)

Where:

$\eta$ - Efficiency of fan, dimensionless.

$\dot W$ - Electric power supplied fan, measured in watts.

$\dot K$ - Rate of change of kinetic energy of air in time, measured in watts.

From definition of kinetic energy, the equation above is now expanded:

$\dot W = \frac{\rho_{a}\cdot \dot V}{2\cdot \eta}\cdot \left(\frac{\dot V}{A_{s}} \right)^{2}$ (Eq. 2)

Where:

$\rho_{a}$ - Density of air, measured in kilograms per cubic meter.

$\dot V$ - Volume flow, measured in cubic meters per second.

$A_{s}$ - Cross-sectional area of fan, measured in square meters.

If we know that $\rho_{a} = 1.20\,\frac{kg}{m^{3}}$ , $\dot V = 0.05\,\frac{m^{3}}{s}$ , $\eta = 0.3$ and $A_{s} = 20\times 10^{-4}\,m^{2}$ , the power needed to be supplied by the fan is:

$\dot K = \left[\frac{\left(1.20\,\frac{kg}{m^{3}} \right)\cdot \left(0.05\,\frac{m^{3}}{s} \right)}{2\cdot (0.3)} \right]\cdot \left(\frac{0.05\,\frac{m^{3}}{s} }{20\times 10^{-4}\,m^{2}} \right)^{2}$

$\dot K = 62.5\,W$

A fan with an energy efficiency of 30 % would need 62.5 watts to bring a desired volume flow of 0.05 cubic meters per second through a cross-sectional area of 20 square centimeters.

5 0

3 years ago

A boat produced water waves of frequency 4 Hz and wavelength 2m, if it reached the shore after 2 seconds how far is the boat fro

kap26 [50]

Answer:

S = 16 m

Explanation:

Given that

The frequency of the water waves, f = 4 Hz

The wavelength of the water waves, λ = 2 m

The time the waves reached the shore, t = 2 s

The relation between the velocity, wavelength, and the frequency of the wave is given by the relation,

v = f λ m/s

Substituting the given values in the above equation,

v = 4 x 2

= 8 m/s

The velocity of the water waves is v = 8 m/s

The distance between the shore and boat is given by

s = v x t

= 8 x 2

= 16 m

Hence, the distance between the boat and the shore is, s = 16 m

7 0

3 years ago

Question 10 of 10 When light passes through a small opening in a barrier, it bends to spread out on the other side of the openin

suter [353]

Answer:

C. It is the result of diffraction

Explanation:

I just took the test

7 0

2 years ago

Read 2 more answers

**URGENT PLEASE HELP**

nalin [4]

Answer:

This depends on what angle they are approaching each other before they collided.The two simple cases are if they are running in the same direction or opposite direction from each other. For either case, use the conservation of momentum equation to solve: M_total*V_result = M1*V1 + M2*V2

Explanation:

Here are two possible solutions.

Head-on collision: M1=78, V1=8.5, M2=72, V2=-7.5 (that's negative because he's running the other way), M_total = 78+72 = 150, so V_result = (78*8.5 - 72*7.5)/150 = 0.82 m/s. Sanity check, they weigh about the same and so most of their velocity should cancel out.

Running the same way: change the sign of V2 to positive so V_result = (78*8.5 + 72*7.5)/150 = 8.02 m/s. Sanity check, they weigh about the same and the resultant speed is between the two starting velocities.

<em>hope it helps:)</em>

7 0

3 years ago

Read 2 more answers

If the resistance of an electric circuit is 12 ohms and the voltage in the circuit is 60 V, the current flowing through the circ

AnnyKZ [126]

The formula for calculating the current flowing in a circuit is:
I = V /R
Where:
I = current = ?
V = voltage = 60 V
R = resistance = 12 Ohms
I = V /R = 60/ 12 = 5
Therefore, the current flowing through the circuit is 5 A.

7 0

3 years ago

Read 2 more answers