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3 years ago

Astrologists use the positions of the stars to make predictions about the future. Why is astrology a pseudoscience?

2 answers:

7 0

Because it is a collection of beliefs mistakenly regarded as being based as specific method

please can i have a brainliest

Helen [10]3 years ago

5 0

Because there is no scientifically credible evidence that the positions of the stars have any effect on the future.

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The following table lists the work functions of a few common metals, measured in electron volts. Metal Φ(eV) Cesium 1.9 Potassiu

Citrus2011 [14]

A. Lithium

The equation for the photoelectric effect is:

$E=\phi + K$

where

$E=\frac{hc}{\lambda}$ is the energy of the incident light, with h being the Planck constant, c being the speed of light, and $\lambda$ being the wavelength

$\phi$ is the work function of the metal (the minimum energy needed to extract one photoelectron from the surface of the metal)

K is the maximum kinetic energy of the photoelectron

In this problem, we have

$\lambda=190 nm=1.9\cdot 10^{-7}m$ , so the energy of the incident light is

$E=\frac{hc}{\lambda}=\frac{(6.63\cdot 10^{-34}Js)(3\cdot 10^8 m/s)}{1.9\cdot 10^{-7} m}=1.05\cdot 10^{-18}J$

Converting in electronvolts,

$E=\frac{1.05\cdot 10^{-18}J}{1.6\cdot 10^{-19} J/eV}=6.5 eV$

Since the electrons are emitted from the surface with a maximum kinetic energy of

K = 4.0 eV

The work function of this metal is

$\phi = E-K=6.5 eV-4.0 eV=2.5 eV$

So, the metal is Lithium.

B. cesium, potassium, sodium

The wavelength of green light is

$\lambda=510 nm=5.1\cdot 10^{-7} m$

So its energy is

$E=\frac{hc}{\lambda}=\frac{(6.63\cdot 10^{-34}Js)(3\cdot 10^8 m/s)}{5.1\cdot 10^{-7} m}=3.9\cdot 10^{-19}J$

Converting in electronvolts,

$E=\frac{3.9\cdot 10^{-19}J}{1.6\cdot 10^{-19} J/eV}=2.4 eV$

So, all the metals that have work function smaller than this value will be able to emit photoelectrons, so:

Cesium

Potassium

Sodium

C. 4.9 eV

In this case, we have

- Copper work function: $\phi = 4.5 eV$

- Maximum kinetic energy of the emitted electrons: K = 2.7 eV

So, the energy of the incident light is

$E=\phi+K=4.5 eV+2.7 eV=7.2 eV$

Then the copper is replaced with sodium, which has work function of

$\phi = 2.3 eV$

So, if the same light shine on sodium, then the maximum kinetic energy of the emitted electrons will be

$K=E-\phi = 7.2 eV-2.3 eV=4.9 eV$

7 0

3 years ago

Citrus2011 [14]

Answer:

net force is positive downward..B

6 0

2 years ago

Lightning produces a maximum air temperature on the order of 104K, whereas a nuclear explosion produces a temperature on the ord

gtnhenbr [62]

Answer:

tex]2.898\times 10^{-7}\ \text{m}[/tex] ultraviolet region

$2.898\times 10^{-10}\ \text{m}$ x-ray region

Explanation:

T = Temperature

b = Constant of proportionality = $2.898\times 10^{-3}\ \text{m K}$

$\lambda$ = Wavelength

$T=10^4\ \text{K}$

From Wein's law we have

$\lambda=\dfrac{b}{T}\\\Rightarrow \lambda=\dfrac{2.898\times 10^{-3}}{10^4}\\\Rightarrow \lambda=2.898\times 10^{-7}\ \text{m}$

The wavelength of the radiation will be $2.898\times 10^{-7}\ \text{m}$ and it is in the ultraviolet region.

$T=10^7\ \text{K}$

$\lambda=\dfrac{2.898\times 10^{-3}}{10^7}\\\Rightarrow \lambda=2.898\times 10^{-10}\ \text{m}$

The wavelength of the radiation will be $2.898\times 10^{-10}\ \text{m}$ and it is in the x-ray region.

5 0

2 years ago

Distinguish between contact force and non-contact forces give three examples of each

Artist 52 [7]

Answer:

1. the force which can be felt or act only when two objects are in contact is known as contact force.

for example: frictional force, muscular force,

tension, air resistance .

2. the force which can be felt or act even when two objects are in contact or not is known as non-contact force.

for example: magnetic force, gravitational force, electrostatic force.

6 0

2 years ago

What causes melting of material under divergent plate boundaries?

Triss [41]

Melting: as mantle material rise toward the divergent plate boundary the pressure is reduced which causes melting

5 0

3 years ago