Photoelectric Effect — Important Questions
ICSE · Class 12 · Physics
70 important questions from Photoelectric Effect for ICSE Class 12 Physics, with answers. Written for the board exams 2027.
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Important Questions from Photoelectric Effect
A photon has wavelength 3300 Å. Find its momentum in kg m s^-1.
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2.0 × 10^-27 kg m s^-1
Use p = h/λ. Convert 3300 Å to 3300 × 10^-10 m = 3.3 × 10^-7 m. Then p = 6.6 × 10^-34 / 3.3 × 10^-7 = 2.0 × 10^-27 kg m s^-1.
A photon of wavelength 3300 Å has equivalent mass. Find its equivalent mass in kg.
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6.67 × 10^-36 kg
Use m = h/(cλ). With λ = 3.3 × 10^-7 m, m = 6.6 × 10^-34 / (3.0 × 10^8 × 3.3 × 10^-7) = 6.67 × 10^-36 kg.
A photon has energy 10.2 eV. Find its momentum in kg m s^-1 using E = pc.
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5.44 × 10^-27 kg m s^-1
Convert 10.2 eV to joule: 10.2 × 1.6 × 10^-19 = 1.632 × 10^-18 J. Then p = E/c = (1.632 × 10^-18)/(3.0 × 10^8) = 5.44 × 10^-27 kg m s^-1.
An isolated hydrogen atom emits a photon of energy 10.2 eV. Find the kinetic energy of the recoil atom in joule.
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9.25 × 10^-27 J
Photon momentum is 5.44 × 10^-27 kg m s^-1. Recoil kinetic energy K = p^2/(2m). Using m = 1.6 × 10^-27 kg, K = (5.44 × 10^-27)^2 / (2 × 1.6 × 10^-27) = 9.25 × 10^-27 J.
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