NEET Dual Nature of Matter — Set 1

Question 1

Light of wavelength $ 450 \, \text{nm} $ produces a photocurrent that stops at $ 0.9 \, \text{V} $. What is the threshold frequency? (Take $ h c = 1240 \, \text{eV nm} $, $ h = 6.63 \times 10^{-34} \, \text{J s} $)

Accepted Answer

$ E = \frac{h c}{\lambda} = \frac{1240}{450} \approx 2.76 \, \text{eV} $. $ K_{\max} = e V_0 = 0.9 \, \text{eV} $. $ \phi_0 = E - K_{\max} = 2.76 - 0.9 = 1.86 \, \text{eV} $. $ v_0 = \frac{\phi_0}{h} = \frac{1.86 \times 1.6 \times 10^{-19}}{6.63 \times 10^{-34}} \approx 4.49 \times 10^{14} \, \text{Hz} $.

Question 2

A photon has an energy of $ 5.0 \times 10^{-19} \, \text{J} $. What is its frequency? (Take $ h = 6.63 \times 10^{-34} \, \text{J s} $)

Accepted Answer

$ E = h v $. $ v = \frac{E}{h} = \frac{5.0 \times 10^{-19}}{6.63 \times 10^{-34}} \approx 7.54 \times 10^{14} \, \text{Hz} $.

Question 3

The maximum kinetic energy of photoelectrons is $ 1.0 \, \text{eV} $ when light of wavelength $ 500 \, \text{nm} $ is used. What is the threshold frequency of the metal? (Take $ h c = 1240 \, \text{eV nm} $)

Accepted Answer

$ E = \frac{h c}{\lambda} = \frac{1240}{500} = 2.48 \, \text{eV} $. $ \phi_0 = E - K_{\max} = 2.48 - 1.0 = 1.48 \, \text{eV} $. $ v_0 = \frac{\phi_0}{h} = \frac{1.48 \times 1.6 \times 10^{-19}}{6.63 \times 10^{-34}} \approx 3.57 \times 10^{14} \, \text{Hz} $.

NEET Physics: Dual Nature of Matter — Practice Set 1

Q1. Light of wavelength \( 450 \, \text{nm} \) produces a photocurrent that stops at \( 0.9 \, \text{V} \). What is the threshold frequency? (Take \( h c = 1240 \, \text{eV nm} \), \( h = 6.63 \times 10^{-34} \, \text{J s} \))

Q2. A photon has an energy of \( 5.0 \times 10^{-19} \, \text{J} \). What is its frequency? (Take \( h = 6.63 \times 10^{-34} \, \text{J s} \))

Q3. The maximum kinetic energy of photoelectrons is \( 1.0 \, \text{eV} \) when light of wavelength \( 500 \, \text{nm} \) is used. What is the threshold frequency of the metal? (Take \( h c = 1240 \, \text{eV nm} \))

Q4. What does the photoelectric effect demonstrate about the nature of light?

Q5. A photon has momentum \( 1.5 \times 10^{-27} \, \text{kg m/s} \). What is its frequency? (Take \( h = 6.63 \times 10^{-34} \, \text{J s} \))

Q6. The maximum frequency of X-rays from a \( 10 \, \text{kV} \) tube is: (Take \( h = 6.63 \times 10^{-34} \, \text{J s} \), \( e = 1.6 \times 10^{-19} \, \text{C} \))

Q7. The work function of a metal is \( 2.2 \, \text{eV} \). What is the threshold wavelength in nm? (Take \( h c = 1240 \, \text{eV nm} \))

Q8. The de Broglie wavelength of an electron moving at \( 2.0 \times 10^6 \, \text{m/s} \) is calculated. What is its value? (Take \( h = 6.63 \times 10^{-34} \, \text{J s} \), \( m_e = 9.11 \times 10^{-31} \, \text{kg} \))

Q9. The stopping potential for photoelectrons is \( 0.7 \, \text{V} \). What is the maximum kinetic energy in eV?

Q10. An electron is accelerated through a potential difference of \( 100 \, \text{V} \). What is its de Broglie wavelength? (Take \( h = 6.63 \times 10^{-34} \, \text{J s} \), \( m_e = 9.11 \times 10^{-31} \, \text{kg} \), \( e = 1.6 \times 10^{-19} \, \text{C} \))