   Chapter 29, Problem 18PE

Chapter
Section
Textbook Problem

Unreasonable ResultsRed light having a wavelength of 700 nm is projected onto magnesium metal to which electrons are bound by 3.68 eV. (a) Use KE e = h f − BE to calculate the kinetic energy of the ejected electrons. (b) What is unreasonable about this result? (c) Which assumptions are unreasonable or inconsistent?

(a)

To determine

The kinetic energy of the ejected electrons.

Explanation

Given:

Wavelength of light =λ=700 nm = 700 × 109 m

Frequency of light =f

Binding energy of metal =BE=3.68 eV

Binding energy =BE

Speed of light =c=3 ×108 ms1

Kinetic energy of ejected electrons =KE

Formula Used:

Frequency is given as,

f=cλ

Energy of light is given as,

E=hf

Kinetic energy of the ejected electrons is given as,

KE=hfBE

Calculation:

Frequency is given as,

f=cλ

Inserting the values

(b)

To determine

The factor that unreasonable about the result in part (a).

(c)

To determine

The assumption which is unreasonable or inconsistent.

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