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3 years ago

Question 31 Unsaved

1 answer:

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A) elements in the same group usually have similar chemical properties
B) This is because their atoms have the same number of electrons in the highest occupied energy shells
C) Lithium, sodium, potassium in group 1 elements are reactive metals called the alkali metals

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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

Read the following questions and answer them using complete sentences. Be sure to fully explain your answers.

astra-53 [7]

Wave power can be regarded as a reliable source of energy because the ocean currents are always moving.

<h3>What can be the challenges of wave power?</h3>

Wave power is a device that can be used to convert the mechanical energy of the ocean waves into electrical energy based on the principle of conservation of energy.

The major challenges that face the use of wave power in electricity generation is the unreliability of the waves which leads to uncertainty in the quantity of power generated Also, the wave direction and direction of ocean currents all limit the amount of power generated by this method. However, in spite of challenges, it can be regarded as a reliable source of energy because the ocean currents are always moving.

Learn more about wave power:brainly.com/question/1362067

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1 year ago

While studying bacterial cells, scientists measure the lengths of the cells in one colony. The chart shows their data. The scien

jok3333 [9.3K]

Answer:

Following are the solution to the given question:

Explanation:

Its best approach to this measurement ought to be to indicate that there was a mistake throughout the calculation, as well as the gathering of further details while researching cells for bacteria, directly measuring the cell length of a colony. This chart illustrates its data, which scientists have observed that there's still a measurement.

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2 years ago

When all else remains the same, what effect would decreasing the focal length have on a convex lens?

aniked [119]

<h3>Answer;</h3>

<u>It would make the lens stronger. </u>

<h3>Explanation;</h3>

The focal length is the distance between the optical center or the center of the lens to the focal point of a convex or concave lens.
The power of the convex lens is lens ability to undertake refraction or bend light. It is given as the reciprocal of focal length.
Power of the lens = 1/ f; therefore the smaller the focal length the higher the power and the larger the focal length the lower the power.
Thus; decreasing the focal length of a convex lens makes the lens stronger.

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3 years ago

Read 2 more answers

An ant clings to the outside edge of the tire of an exercise bicycle. When you start pedaling, the ant's speed increases from ze

konstantin123 [22]

Answer:

1- 3.64 m/s

2- 0.28 m

3- 70.8 rad

4- 19.8 m

Explanation:

see attachment