Question 1

Which statement best describes the photoelectric effect as explained by Einstein?

Accepted Answer

Light consists in bundles of energy called photons, which can eject electrons from metals.

Question 2

Which feature of the photoelectric effect cannot be explained using classical physics?

Accepted Answer

The emission of electrons only occurs above a certain threshold frequency.

Question 3

In a typical photoelectric-effect experiment, which variable is most directly related to the energy of the emitted electrons?

Accepted Answer

The frequency of the incident light.

Question 4

Calculate the energy of a photon with frequency $$f$$ using the appropriate equation.

Accepted Answer

$$E = hf$$

Question 5

Which equation gives the threshold frequency $$f_0$$ for the photoelectric effect?

Accepted Answer

$$f_0$$ = \frac{\phi}{h}$$

Question 6

Given the equation $$E = \frac{hc}{\lambda}$$, what does $$\lambda$$ represent in the context of the photoelectric effect?

Accepted Answer

The wavelength of the incident photon.

Question 7

What is the definition of work function ($$\phi) $$for a metal?

Accepted Answer

The minimum energy required to emit an electron from the metal.

Question 8

Which equation relates the work function $$\phi to $$the threshold wavelength $$\$$lambda_0$$?

Accepted Answer

$$\phi = \frac{hc}{\$$lambda_0$$}$$

Question 9

If the wavelength of incident light is shorter than the threshold wavelength $$\$$lambda_0$$, what happens in a photoelectric experiment?

Accepted Answer

Electrons are emitted with nonzero kinetic energy.

Question 10

How does increasing the intensity of light (while keeping frequency constant above threshold) affect the photoelectric effect?

Accepted Answer

It increases the number of photoelectrons emitted.

Question 11

Which equation relates the maximum kinetic energy of emitted electrons to the photon energy and work function?

Accepted Answer

$$KE_{max} = hf - \phi$$

Question 12

A metal has a threshold wavelength $$\$$lambda_0$$ = 400\,nm. $$What is its work function $$\phi in $$electron volts (eV)? (Use $$h = 6.63 	imes 10$$^{-34}$$\,Js$$, $$c = 3.00 	imes 10^8$\,m/s$$, $$1\,eV = 1.60 	imes 10$$^{-19}$$\,J)$$

Accepted Answer

$$\phi = 3.1\,eV$$

Question 13

If the stopping potential $$V_0 in a $$photoelectric experiment is measured to be $$2.0\,V$$, what is the maximum kinetic energy of the emitted electrons?

Accepted Answer

$$KE_{max} = eV_0$ = 2.0\,eV$$

Question 14

Which of the following best describes the effect of increasing the wavelength of incident light (while keeping intensity constant) in a photoelectric experiment?

Accepted Answer

The maximum kinetic energy of emitted electrons decreases.

Question 15

A photon with energy $$E_{photon}$$ strikes a metal with work function $$\phi. $$Which equation gives the maximum kinetic energy of the emitted electron?

Accepted Answer

$$KE_{max} = E_{photon} - \phi$$

Question 16

In a photoelectric experiment, what is the physical meaning of the threshold frequency $$f_0$$?

Accepted Answer

The minimum frequency of light required to emit electrons from the metal.

Question 17

Which graph best represents the relationship between maximum kinetic energy of photoelectrons and frequency of incident light?

Accepted Answer

A straight line with a positive slope starting at the threshold frequency.

Question 18

If the intensity of light is doubled but the frequency remains constant and above threshold, what happens to the maximum kinetic energy of photoelectrons?

Accepted Answer

It remains unchanged.

Question 19

A photoelectric experiment uses light of wavelength $$\lambda = 300\,nm on a $$metal with threshold wavelength $$\$$lambda_0$$ = 400\,nm. $$Which equation gives the maximum kinetic energy of the emitted electrons?

Accepted Answer

$$KE_{max} = hc \left( \frac{1}{\lambda} - \frac{1}{\$$lambda_0$$} \right)$$

Quantum Theory: The Photoelectric Effect

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