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题型分析 Question Types

类型 A: 光子能量与动量计算​

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Example 1 (9702_w20_qp_41 Q11b): 光子动量和能量转移

入射 λ=540\lambda = 540 nm, 散射 λ=544\lambda = 544 nm, 与电子弹性碰撞

  • C1 p=h/λp = h/\lambda
  • A1 p=6.63×10−34/(544×10−9)=1.22×10−27p = 6.63 \times 10^{-34} / (544 \times 10^{-9}) = 1.22 \times 10^{-27} N s
  • C1 energy =hc(1/λ1−1/λ2)= hc(1/\lambda_1 - 1/\lambda_2)
  • A1 =6.63×10−34×3.00×108×(540−1−544−1)×109=2.7×10−21= 6.63 \times 10^{-34} \times 3.00 \times 10^8 \times (540^{-1} - 544^{-1}) \times 10^9 = 2.7 \times 10^{-21} J

Example 2 (9702_s20_qp_41 Q11a): 正负电子湮灭

电子+正电子 → 两个 γ\gamma 光子

  • C1 E=mc2E = mc^2
  • A1 =9.11×10−31×(3.0×108)2=8.2×10−14= 9.11 \times 10^{-31} \times (3.0 \times 10^8)^2 = 8.2 \times 10^{-14} J
  • C1 p=E/cp = E/c
  • A1 =8.2×10−14/3.0×108=2.7×10−22= 8.2 \times 10^{-14} / 3.0 \times 10^8 = 2.7 \times 10^{-22} N s
  • B1 momentum conserved → photons emitted in opposite directions

Example 3 (9702_s21_qp_41 Q12b): 光电效应计算

λ=250\lambda = 250 nm, EK,max=1.4E_{K,\text{max}} = 1.4 eV

  • C1 E=hc/λE = hc/\lambda
  • C1 E=6.63×10−34×3.00×108/(250×10−9)E = 6.63 \times 10^{-34} \times 3.00 \times 10^8 / (250 \times 10^{-9})
  • A1 =5.0= 5.0 eV
  • C1 Φ=hf−EK,max\Phi = hf - E_{K,\text{max}}
  • A1 =5.0−1.4=3.6= 5.0 - 1.4 = 3.6 eV

类型 B: 光电效应解释​

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Example 1 (9702_s21_qp_41 Q12a): 为什么光电子的最大动能与光强无关

  • B1 frequency determines energy of photon
  • B1 intensity determines number of photons (per unit time)
  • B1 intensity does not determine energy of a photon
  • B1 kinetic energy (of electron) depends on energy of one photon

Example 2 (9702_w22_qp_41 Q8a): 功函数定义

  • B1 photon energy (to remove electron)
  • B1 minimum energy to remove electron

Example 3 (9702_w22_qp_41 Q8c): 频率增加，功率不变

  • M1 greater photon energy (and same work function)
  • A1 so maximum kinetic energy is increased
  • M1 (greater photon energy and same power so) lower number of photons per unit time
  • A1 so lower rate of emission

类型 C: 电子衍射与 de Broglie 波长​

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Example 1 (9702_s23_qp_41 Q7a): de Broglie 波长定义

  • B1 wavelength associated with a moving particle

Example 2 (9702_s23_qp_41 Q7b): 电子衍射实验

石墨晶体后荧光屏上出现同心圆环图案

  • B1 (electron) diffraction
  • B1 beam spreads out indicating diffraction
  • B1 electron beam is behaving as a wave

Example 3 (9702_s23_qp_41 Q7c): 增大加速电压

  • B1 (greater p.d. so) electrons have greater momentum
  • B1 greater momentum so decrease in (de Broglie) wavelength
  • B1 lower wavelength causes: smaller diffraction angle (rings closer together)

类型 D: 能级与光谱​

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Example 1 (9702_s20_qp_41 Q10a): 白光通过冷低压气体的吸收光谱

B4 (any four):

  • photon gives energy to electron in an inner shell
  • electron moves from lower to higher energy level
  • energy (of photon) is equal to difference in energy levels
  • electron de-excites giving off photon (of same energy)
  • photons emitted in all directions

Example 2 (9702_s20_qp_41 Q10b): 用能带理论解释 LDR

  • B1 photons give energy to electrons in VB
  • B1 electron crosses FB/jumps to CB
  • B1 (positive) holes left/created in VB
  • B1 low intensity: few electrons in CB / most electrons in VB
  • B1 more charge carriers results in lower resistance