Quantum Flashcards
(29 cards)
What is stopping potential used for ?
It is used to experimentally measure the Ke(max) of electrons as frequency is adjusted.
What is the photoelectric effect ?
The photoelectric effect is caused when light incident on a metal surface causes electrons to emitted from the surface from the metal.
What is expected to occur when electrons are used in double slit experiment and what actually happens ?
As electrons are particles you expect them to create two lines (like a stencil and paint)
but what actually happens is the electrons produce a diffraction pattern.
What is a continuous spectrum ?
spectrum where all wavelengths are emitted.
How do you convert J to eV ?
x/1.6x10^-19 (hint: value of eV is always a lot larger)
Why are the electrons emitted with a range of Ke ?
Some electrons are embedded deeper in the surface of the metal so more E is required to escape.
What is the work function ?
the minimum energy required to liberate an electron from the surface of a metal
What is the threshold frequency of a metal ?
the threshold frequency is the minimum frequency of light incident on a metal surface needed to cause electrons to be emitted.
For an electron to absorb energy and excite what must be the case ?
IT absorbs the exact amount of energy between the two energy levels. either a photon with exact energy of electron with E more than difference and leaves with difference of E as Ke.
What is the formula linking Ek(max) and stopping potential.
Ek(max) = e V(stopping)
What is the formula for the work function ?
Φ = h f0
What is a emission line spectrum ?
When only specific wavelengths are emitted. (exciting hot gas)
When f > f0 hat does increasing the brightness do ?
Increases the amount of electrons emitted per second.
On a F Ek(max) graph what are the intercepts and gradient ?
X-int is threshold frequency
Y-int is work function
gradient is h plank constant (6.63x10^-34)
What is the formula for de broglie wavelength and what is it ?
λ = h/p
de broglie wavelength is the effective wavelength of a particle.
Explain how fluorescent lights work.
Current is passed through mercury gas which is at low pressure.
Atomic electrons gain E from incident electrons and excite then de-excite and emit UV.
Phosphor coating on light absorbs UV and atomic electrons excite and de-excite then emit visible light.
Why must we think of light as a particle ?
The photoelectric effect cannot be proven when light is a wave.
How do you work out Ke of a emitted electron ?
Photon energy = Φ + Ek
What is a absorption line spectrum ?
When all wavelengths are emitted excluding specific frequencies. (continuous spectrum shone through cold gas)
What is excitation ?
When an electron moves from low energy level to a higher.
What is the relationship of frequency f photons and Ke of electrons ?
Higher frequency the higher Ke(max) of the electrons.
What is a stopping potential circuit look like and how does it work ?
A photoemissive surface opposite a wire electrode in series with a cell and a ammeter (micro amp)
The negative terminal off cell points towards electrode, the electrons from the photoemisssive circuit oppose electrons from cell and when A = 0 the voltage of cell multiplied by e is equal to Ek(max).
Why does increasing the brightness of the light not change anything when f>f0
Frequency is still under F0 so no change.
What are the conditions for double slit for a particle to form a diffraction pattern ?
de broglie wavelength must be similar (within 100x) to slit separation.
