4.5 | quantum physics

what is the photon model of electromagnetic radiation?

electromagnetic radiation travels as a continuous wave but interacts with matter as discrete energy quanta called photons.

what is the relationship between the energy of a photon and its frequency?

the energy of a photon is directly proportional to its frequency.

what is the planck constant?

6.63×10^-34 Js.

what is the electronvolt (eV) and how is it defined?

the energy transferred when an electron travels through a potential difference of 1 volt, equal to 1.60×10^-19 joules.

how can LEDs be used to estimate the value of the planck constant?

by measuring the potential difference required to turn on an LED and knowing the wavelength of emitted light, the planck constant can be calculated by eV = hc/lambda.

what is the photoelectric effect?

the release of electrons from a metal surface when electromagnetic radiation is shone on it.

how can the photoelectric effect be demonstrated?

using a gold leaf electroscope, where UV light causes electrons to be released from a zinc plate, resulting in the gold leaf falling back to the stem.

what is the work function (ϕ) of a metal?

the minimum energy required to free an electron from the surface of the metal.

what is einstein's photoelectric equation?

hf = work function + KEmax

what is the significance of the threshold frequency in the photoelectric effect?

the minimum frequency required for photons to release electrons from the metal surface.

how does the intensity of radiation affect electron emission in the photoelectric effect?

the intensity does not affect whether electrons are released; it only increases the rate of emission if the frequency is above the threshold.

what is wave-particle duality?

the concept that electromagnetic radiation and matter exhibit both wave-like and particle-like properties.

what is the de broglie equation?

lambda = h/p

how does mass affect the wavelength of a particle according to the de broglie equation?

as the mass of the particle increases, its wavelength decreases, making wavelike properties harder to observe.

how can electrons demonstrate wave-particle duality?

electrons can be diffracted, producing a diffraction pattern, which is a property associated with waves, despite being classified as particles.

what happens when visible light is shone on a metal surface in the photoelectric effect?

no electrons are released, regardless of the intensity of the visible light.

what is the effect of increasing the frequency of radiation above the threshold frequency?

increasing the frequency increases the maximum kinetic energy of the emitted electrons.

what is the role of excess energy in the photoelectric effect?

excess energy from the photon above the work function becomes the kinetic energy of the emitted electron.

what is the significance of using different colored LEDs in the experiment to determine the planck constant?

using different colored LEDs allows for varying wavelengths and threshold p.d., improving the accuracy of the calculated value of h.

what is the formula that relates the speed of light and the wavelength of electromagnetic radiation?

c = f lambda

what is the role of a potential divider in the LED experiment?

it is used to vary the voltage through the LED to find the threshold potential difference.

how does the photoelectric effect challenge the wave model of electromagnetic radiation?

it demonstrates that light has particle-like properties, as it requires photons to release electrons.

what is the significance of the gradient of the graph of V against 1/λ in the LED experiment?

the gradient is equal to hc/e, allowing for the calculation of the planck constant.

what happens to the gold leaf in a gold leaf electroscope when UV light is shone on it?

the gold leaf gradually falls back to the stem as electrons are released from the zinc plate, reducing the negative charge.

what is the effect of intensity on the energy of emitted electrons in the photoelectric effect?

intensity affects the number of photons and thus the rate of electron emission, but not the energy of individual emitted electrons.

what is the relationship between the energy of a photon and its wavelength?

the energy of a photon is inversely proportional to its wavelength.