Wave nature of electrons and de Broglie wavelengthEdexcel International A Level Physics: Flashcards
What these 12 flashcards ask
- What do electron diffraction experiments show?
- What is seen when electrons pass through thin graphite onto a fluorescent screen?
- Why is the electron diffraction tube evacuated?
- State the de Broglie equation.
- What does h stand for in the de Broglie equation?
- What is the effect on λ of doubling an electron's speed?
- Why do we not see wave effects for a moving tennis ball?
- Why is a diffraction pattern evidence for wave behaviour?
- Why must the electron wavelength be similar to the atomic spacing?
- How does the pattern change if electrons are accelerated more?
- Why can an electron microscope resolve finer detail than a light microscope?
- How do you find λ if you know an electron's kinetic energy?
Exam questions on Wave nature of electrons and de Broglie wavelength
- A physics technician is demonstrating an electron diffraction tube. Electrons from a heated filament are accelerated and directed at a very thin polycrystalline graphite film inside an evacuated glass tube. A fluorescent screen beyond the film shows a pattern of concentric bright rings.Explain why the ring pattern is evidence for the wave nature of electrons.2 marks
- A teacher compares the behaviour of electrons with that of larger moving objects such as a tennis ball. She uses the de Broglie equation, with Planck constant h = 6.63 × 10⁻³⁴ J s and electron mass 9.11 × 10⁻³¹ kg, and considers an electron moving at 4.0 × 10⁶ m s⁻¹ in a vacuum.Calculate the de Broglie wavelength of the electron moving at 4.0 × 10⁶ m s⁻¹.2 marks
- Electrons in a beam have a kinetic energy of 4.0 × 10⁻¹⁷ J. The beam is directed at a crystal in which the spacing between neighbouring layers of atoms is 0.21 nm. A student wants to know whether the electrons will be noticeably diffracted by the crystal.Calculate the speed of an electron with kinetic energy 4.0 × 10⁻¹⁷ J.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).