photons Flashcards
What is a photon
A discrete packet of electromagnetic energy
definition of the electronvolt
The energy transferred to or from an electron when it is passes through a potential difference of 1 volt.
photons properties
travel at the speed of light in a vacuum
there are massless
formula that relates energy with frequency
E=hf
what’s h
the plank constant. 6.63 x 10^-34
Students seek to use the set-up to record data that will help them to calculate a value of Planck’s constant. Which of the following describes the data that should be collected?
Students should gradually increase the voltage and record the value at which the LED turns on. The experiment should be repeated with a number of different LEDs. The wavelength of each LED should also be recorded.
Diodes are circuit components that only switch on once the potential difference across it exceeds its ________ voltage.
threshold
which light emitting diode will light up first if we are slowly increasing the voltage?
purple
blue
green
orange
yellow
red
red
Using the gradient of the V against (1/λ) graph, the value of Planck’s constant can be calculated. Which of the options below gives the correct equation for Planck’s constant?
h = e/c x gradient
Define photoelectric effect
When electromagnetic radiation is shone on to a metal, electrons are released from the surface
of the metal. This is known as the photoelectric effect.
Greater photoelectric effect is seen when … light is shone to a golf leaf
UV, as no matter the intensity shone visible light may have no electrons will be removed from the gold leaf. This is because the electrons have to gain energy from a colliding photon to not only overcome the attractive forces but also use it part of it to escape from the atom/material. The energy they use to escape from the atom is called kinetic energy
Define the work function phi
The work function, ϕ, of a metal is the minimum energy required to free an electron from the surface of the metal.
Why can’t shone visible light at great intensity remove any electrons of a metal
Each photon must have energy at least as great as the work function to release an electron. Energy is proportional to frequency, thus only EM waves with greater frequency such as UV can produce the photoelectric effect. Hence, there is a threshold frequency for the electromagnetic radiation, which is the minimum frequency required to free
electrons from the surface of the metal
the photoelectric
equation
hf = phi + KE max
How would it affect the photoelectric effect If the intensity of a EM wave changes, which frequency is below the frequency threshold
No photoelectric effect will happen
