#1 Homework

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Name: ______________________________

Section: _____________________________

Student ID#:__________________________

Q1.1

Rigel is the brightest star in the constellation Orion and the seventh brightest star in the night sky. Rigel has an emission spectrum that peaks at ~145 nm. What is the surface temperature of Rigel? How does this temperatures compare with our sun?

Rigel,_Rutherfurd_Observatory,_09_September_2014.jpeg

The seventh brightest star in the night sky, Rigel. As viewed from the Rutherfurd Observatory in midnight, the picture was processed through a telescope. Image used with permission (CC-BY-SA 3.0 Haktarfone)

Q1.2

Find the longest-wavelength photon that can eject an electron from potassium, given that the work function is 2.24 eV. Is this visible electromagnetic radiation?

Q1.3

Light with an intensity of 10.0 W is incident on an electroplated copper electrode (W = 4.7eV).

Electrons with a minimum kinetic energy (KE) of 49 eV are ejected from the copper surface. Calculate the frequency of the incident light.
Calculate the maximum number of electrons that can be ejected by a 2.0-second pulse of the incident light (under constant power as indicated).
If the energy of incident light were < \(7.00 \times 10^{-19}\; J\), how many electrons will be emitted?

Q1.4

A laser with a power output of 2.00 mW at a wavelength of 400 nm is projected onto calcium metal.

How many electrons per second are ejected?
What power is carried away by the electrons, given that the work function is 2.71 eV?

Q1.5

Calculate the wavelength of an ultraviolet transition in the Lyman emission series of Hydrogen gas from the n = 2 level and to the n= 1 level. (We just started this in class, but the readings continue it nicely).

Q1.6

A \(500\; g\) sample of water absorbs infrared radiation at \(1.06 \times 10^4\) nm from a carbon dioxide laser that is converted 100% into to heat. Calculate the number of photons at this wavelength required to raise the temperature of the water by \(10^{o}C\). The specific heat capacity of water is \(4.184\dfrac{J}{g^{o}C}\). (Hint: this is a classic heat of reaction calorimetry like problem).

Q1.7

How many grams of ice can be melted after the absorption of \(4.0 \times 10^{23}\) photons at 150 nm? Given that the specific heat of fusion for water is 333.55 kJ/kg at 0° C, how many water molecules will be converted from ice into water after the absorption of these photons?