Practise using photoelectric, interference and electron-diffraction evidence for wave-particle duality and calculating de Broglie wavelength from momentum.
State one piece of experimental evidence for:
the particulate nature of electromagnetic radiation
the wave nature of matter.
Calculate the de Broglie wavelength of an alpha-particle moving at a speed of .
The speed v of the alpha-particle in (b)(i) is gradually reduced to zero.
On Fig. 8.1, sketch the variation with v of .
Fig. 8.1
Suggest an explanation for why people are not observed to diffract when they walk through a doorway.
State the formula for the de Broglie wavelength of a moving particle.
State the meaning of any other symbol used.
Electrons accelerate through a potential difference, pass through a thin crystal and are then incident on a fluorescent screen.
The pattern in Fig. 8.1 is observed on the fluorescent screen.
Fig. 8.1 not to scale
State the name of the phenomenon shown by the electrons at the crystal.
State what this phenomenon shows about the nature of electrons.
Suggest why the thin crystal causes the phenomenon in (b)(i).
The electron is accelerated through a different potential difference. The new pattern observed on the screen is shown in Fig. 8.2.
Fig. 8.2 not to scale
State and explain the change that has been made to the potential difference to create the pattern shown in Fig. 8.2.
State what is meant by the de Broglie wavelength.
Fig. 7.1 shows a glass tube in which electrons are accelerated through a high p.d. to form a beam that is incident on a thin graphite crystal.
Fig. 7.1 (not to scale)
After passing through the graphite crystal, the electrons reach the fluorescent screen. The screen glows where the electrons strike it.
Fig. 7.2 shows the fluorescent screen viewed end-on, from the right-hand side of Fig. 7.1.
Fig. 7.2
State the name of the phenomenon demonstrated by the pattern shown in Fig. 7.2.
Explain what can be concluded from the pattern in Fig. 7.2 about the nature of electrons.
The electrons in (b) are now accelerated through a greater potential difference between the cathode and the anode.
On Fig. 7.3, sketch the pattern that is now seen on the fluorescent screen in Fig. 7.1.
Fig. 7.3
Explain, with reference to de Broglie wavelength, the change in the pattern on the fluorescent screen.
State one piece of experimental evidence for:
the particulate nature of electromagnetic radiation
State what is meant by the de Broglie wavelength.
A particle of matter moves with momentum p.
State the equation that gives the effective wavelength of the particle. State the name of any other symbols used.
Electrons are accelerated from rest through a potential difference (p.d.) of 4.8 kV .
Calculate the effective wavelength of a beam of electrons moving at the speed in (c)(i).
wavelength = m