The Photoelectric Effect - AP Physics 2

1. What is the unit of the work function?

   Joules (J). Energy units, since work function represents minimum energy required.

2. What does $E_k$ represent in the photoelectric equation?

   Kinetic energy of emitted electrons. Energy of motion possessed by electrons after photoemission occurs.

3. If $E_k = 0$, what condition holds in the photoelectric equation?

   $hf = \text{work function}$. Threshold condition where photon energy exactly equals work function.

4. What is the unit of frequency?

   Hertz (Hz). Standard SI unit for oscillations per second in wave phenomena.

5. What is the result of increasing the stopping potential?

   Reduces current to zero. Reverse voltage prevents electrons from reaching collector electrode.

6. What is the effect of increasing light frequency on emitted electrons?

   Increases kinetic energy of electrons. Higher frequency means more energetic photons and faster emitted electrons.

7. What happens if light intensity increases but frequency is constant?

   More electrons emitted; kinetic energy unchanged. More photons increase electron quantity while frequency determines individual energy.

8. Which equation relates energy and frequency of a photon?

   $E = hf$. Planck's relation defining quantized energy packets of electromagnetic radiation.

9. Calculate stopping potential for $E_k = 3 \text{ eV}$.

   $V_s = 3 \text{ V}$. Maximum kinetic energy in eV numerically equals stopping potential in volts.

10. What is the relation between stopping potential and maximum kinetic energy?

    Directly proportional. Higher electron kinetic energy requires proportionally higher stopping voltage.

11. What is the photoelectric effect?

    Emission of electrons from a material when light shines on it. Light energy ejects electrons when photon energy exceeds material's binding energy.

12. What is the work function in the photoelectric effect?

    Minimum energy needed to remove an electron from a material. Material-specific binding energy threshold for electron emission.

13. Which constant is $6.626 \times 10^{-34} \text{ J s}$?

    Planck's constant. Fundamental quantum constant relating energy to frequency in photon interactions.

14. What is the photoelectric work function symbol?

    $\text{work function}$ or $\text{W}$. Standard symbols representing minimum energy for electron removal from material.

15. What happens if the light frequency is below the threshold frequency?

    No electrons are emitted. Insufficient photon energy cannot overcome the material's work function.

16. Calculate frequency for wavelength $500 \text{ nm}$.

    $f = 6.00 \times 10^{14} \text{ Hz}$. Using $f = c/\lambda$ with $\lambda = 500 \times 10^{-9} \text{ m}$.

17. What is the effect of a higher work function on electron emission?

    Requires higher frequency light to eject electrons. Greater binding energy demands more energetic photons for electron liberation.

18. What is the unit of Planck's constant?

    Joule-seconds (J s). Energy-time units reflecting quantum action in electromagnetic interactions.

19. What is the effect of increasing light intensity on electron emission?

    Increases number of electrons emitted. More photons hit surface, but individual electron energy remains constant.

20. State Einstein's photoelectric equation.

    $E_k = hf - \text{work function}$. Photon energy minus work function equals electron's kinetic energy.

21. How does light frequency affect the kinetic energy of electrons?

    Higher frequency increases kinetic energy. More energetic photons transfer greater kinetic energy to ejected electrons.

22. What is the relationship between frequency and energy of light?

    Directly proportional. Higher frequency photons carry more energy: $E = hf$.

23. What effect does increasing light intensity have on photocurrent?

    Increases photocurrent. More photons create greater electron flow in photoelectric circuit.

24. What is the kinetic energy of ejected electrons?

    $E_k = hf - \text{work function}$. Excess photon energy after overcoming work function becomes electron motion energy.

25. What is the significance of the threshold frequency $f_0$?

    Minimum frequency needed to eject electrons. Frequency below this value provides insufficient energy for electron ejection.

26. In the photoelectric effect, what is the role of photon energy?

    Provides energy to eject electrons. Photon transfers its energy to overcome binding forces and accelerate electrons.

27. Convert $2 \text{ eV}$ to joules.

    $3.20 \times 10^{-19} \text{ J}$. Using conversion $1 \text{ eV} = 1.6 \times 10^{-19} \text{ J}$.

28. Identify one factor that does not affect the kinetic energy of emitted electrons.

    Light intensity. Intensity affects electron quantity, not individual electron energy.

29. Find the work function if $hf = 4 \text{ eV}$ and $E_k = 1 \text{ eV}$.

    $\text{work function} = 3 \text{ eV}$. Rearranging Einstein's equation: work function $= hf - E_k$.

30. Calculate the photon energy for $f = 6 \times 10^{14} \text{ Hz}$.

    $E = 3.98 \times 10^{-19} \text{ J}$. Using $E = hf$ with $h = 6.626 \times 10^{-34} \text{ J s}$.

31. Which law does the photoelectric effect contradict in classical physics?

    Wave theory of light. Classical theory predicted continuous energy dependence on intensity, not frequency.

32. What does $h$ represent in the photoelectric equation?

    Planck's constant. Fundamental constant linking energy and frequency: $h = 6.626 \times 10^{-34} \text{ J s}$.

33. What is the speed of light in vacuum?

    $c = 3.00 \times 10^8 \text{ m/s}$. Fundamental constant for electromagnetic wave propagation in vacuum.

34. State the equation for stopping potential $V_s$.

    $eV_s = E_k$. Voltage required to stop fastest electrons equals their kinetic energy.

35. Find the maximum kinetic energy if $hf = 5 \text{ eV}$ and $\text{work function} = 2 \text{ eV}$.

    $E_k = 3 \text{ eV}$. Applying Einstein's equation: $E_k = 5 - 2 = 3 \text{ eV}$.

36. State the relationship between photon frequency and wavelength.

    $\text{Frequency} \times \text{Wavelength} = c$. Wave equation $c = f\lambda$ relates electromagnetic wave properties.

37. Identify the effect of increasing voltage on the photoelectric current.

    Increases current until saturation. Forward voltage accelerates electrons until all available electrons flow.

38. Identify the threshold frequency symbol.

    $f_0$. Standard notation for minimum frequency required for electron emission.

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