Fichas
Sin título
Fichas del conjunto (32)
- 1Explain the application of a photodiode What happens when a photodiode is connected to a potential difference?When a semiconductor material that acts like a photodiode absorbs a photon, it liberates a negative electron within the material and increases the conductivity of the material.
A current will result when the photodiode is illuminated, but not when it is in the dark. - 2Explain how photodiodes are used to detect if something in in the way when an automatic garage door opener is closing the garage doorThis type of sensore fires a beam of light onto a photodiode, which creates a photocurrent in a circuit. If an object gets in the way, it will block the beam of light, which will decrease the conductivity of the photodiode. This stops the current, which then flips a switch, causing the door to stop closing and go up again.
- 3How can photocell sensors be used to detect the light levels in an area?As the intensity of light decreases in the area, the conductivity of the photodiode also decreases, an in turn, decrease the photocurrent. The amount of current created is directly related to the amount of light violable.
- 4What is a charged-couple device (CCD)?A device that changes its conductivity when struck by a photon. An array of CCDs is a set of these devices that has been subdivided into small sections called pixels. These arrays are used to detect light and form an image in a digital camera.
- 5What does the array of CCDs consistsof?A thin layer of semiconducting silicon over an insulating layer of silicon dioxde, with electrodes between both. The photoelectric effect is used when an incident photon of visible light strikes the silicon and liberate an electron. Brighter light provides more photons, which liberate more electrons. This allows each pixel to give an accurate measure of the light intensity
- 6Explain the photoelectric effect in solar panelsThe incident photons on the solar cell liberate an electron (the photoelectric effect), changing the conductivity of the semiconducting material and producing a current. The energy conversion changes radiant energy into electrical energy, but it is not very efficient and gets worse when the sunlight is indirect. To improve efficiency, a thin antireflecting coating is placed over the solar cell. Each cell products very little power, so they are connected together in large arrays.
- 7How much energy are arrays are meant to produce? What is the typical efficiency?Many arrays are required to produce enough energy to power a single home and the arrays produce no energy at night.
The typical efficiency of a solar cell is about 20% so one fith of the incident radient energy on the panel is converted into electrical energy; the rest is reflected or produces thermal energy. - 8Use Max Planck's quantum theory to explain the following behaviour of photoelectrons. a) Low-intensity light does not release any photoelectrons. What will happen if the light is made brighter? b) Low-intensity light releases photoelectrons. What will hapen if the light is made brighter? c) Low-intensity light does not release any photoelectrons. What will happen if the frequency of the light is gradually increased?a) Nothing; no current is produced, no matter how intense the light becomes. The is because the energy required to eject a photoelectron directly depends on the frequency and not the intensity. If the frequency of the incoming light is lower than the threshold frequency, the photons cannot provide enough energy for an electron on the surface of a metal to escape.
b) the photons provide enough energy (i.e. frequency above threshold frequency) then increasing the intensity will increase the number of photons which will increase the number of electrophotons. In turn, this will increase the current. Note, increasing the intensity would increase the number of photons regardless of frequency, however, if the frequency was below the threshold frequency, it won’t increase the number of
c) the frequency increases, the kinetic energy and current increases. When the frequency is gradually increased above the threshold, the speed and the kinetic energy of the electrons increase as the electrons will be ejected. However, as the frequency increases above the threshold frequency, the cur - 9Explain Compton scatteringAn incident x-ray photon ejects a photoelectron from a metal but also ejects an x-ray photon that has lower energy than the incident photon. The energy of the incident photon must equal the combined kinetic energy of that photoelectron and scattered photon
- 10It is known that one of five different things can take place when a photon interacts with matter:1. The most common and simple interaction is reflection e.g. photons of visible light reflect off a surface like a mirror
2. A photon can hit matter and produce a photoelectron, while being absorbed in the process
3. A more energetic photon can produce a photoelectorn, lose some energy, and then scatter with less energy (and lower frequency or longer wavelength)
4. A photon can strike an e- in around a nucleus, exciting the e- to a higher energy level. The photon is absorbed
5. In pair production, a very highly energetic photon collides with a heavy nucleus, creating a new electron and positron. - 11Examine the graph, showing the rate of photosynthesis as a function of the wavelength of light. Using the graphs, as well as what you have learned about interactions of photons with matter, explain the following: a) Why leaves containing chlorophyll appear green under white light b) Why monochromatic green light does not produce photosynthesis c) Why low-temperature light bulbs are unable to produce photosynthesis when white light from the sun can do soa) This happens because leaves reflect only the green light .This can be seen on the graph, which shows that green light is not absorbed very well by the leaf.
b) Green light is not absorbed well by leaves. This suggests that the leaf reflects most of this light and does not absorb much energy from it for photosynthesis
c) The low-temperature light bulb does not produce the shorter wavelength of light that tends to promote a greater rate of photosynthesis, as shown on the graph. - 12How can you use the principle of complementarity to help clarify the wave-particle duality of light? What's a general rule for light passing through a medium or free space? What about when interacting with matter?In order to understand a specific experiment, you must use either the wave theory or the photon theory, but not both. To understand how light can produce an interference pattern for two slits, you must use the wave theory and to understand how light can create photoelectrons, you must use the photon theory.
Its behaviour is best explained by the way theory.
It is best explained by particle (photon) theory - 13Explain the effects de Broglie wavelengths have on a) Larger objects like balls, cars and planes b) Smaller particle electronsa) They have extremely short wavelengths that will not have any observable effects on the motion of the objects
b) Have wavelengths comparable to light and these wavelengths could likely have an effect on the motion of the particles - 14When do non-zero mass particles exhibit wave like properties? When do they exhibit particle nature?Through space (or a medium)
When interacting with matter - 15What occurs when particles with a large mass passes through an opening? What about for electrons?Their wavelengths are so small, they don't diffract when passing through relatively large openings, such as a door.
Electrons have wavelengths that are much longer, so they will diffract when passing through small openings, such as the spaces between atoms - 16What is the best resolution of normal optical microscopes? What is the maximum magnification? What is the maximum magnification using de Broglie wavelengths of electrons? What about if the electrons move faster?About 2.0 x 10^-7 m (approx half the wavelength of visible light)
2000 times
up to 300 000 times
over 2 000 000 times - 17Similar to lenses focusing beams of light, what focuses beams of electrons?magnetic fields
- 18What is a transmission electron microscope? What are the lenses made of? What do the lenses do? How are the electrons obtained and what are they accelerated through?Like an optical light microscope except magnetic lenses replace optical ones.
The magnetic lenses are made of circular magnetic coils that create strong magnetic fields. These fields exert a magnetic force on electrons that pass through them. The electrons are then focused in the same way as light is focused ,when passed through a lens.
From a hot filament and are accelerated through large potential differences (50 kV to 100 kV) to increase their speed. - 19Why is it important that the electrons are focused into a parallel beam before passing through the specimen that is being examined (where the specimen is only 20 to 50 nm)Since the electrons will slow down too much or scatter, which will blur the image
- 20What needs to occur in order to avoid scattering and to protect the specimen from damage?it is important for the electrons to pass through a vacuum and the beam of electrons must be applied for short time intervals.
- 21What is a scanning electron microscopeCan form three-dimensional images by moving a beam of electrons across the specimen.
- 22Explain the small tip on the scanning tunneling electron microscope. What does it allow the microscope to create?Uses the small tip of a probe to scan the surface of the specimen. A small potential difference between the tip and the specimen causes surface electrons to leave the probe, creating a current in a process called tunneling.
It allows the microscope to create three-dimensional images the size of atoms and can even form a picture that represents the distribution of the electrons. - 23What will happen to the resolution of the microscope if the energy of the electron is increased? Explain.If the energy of the electrons is increase, their speed will increase, which will decrease the wavelength of the electrons. If the wavelength of the electron decreases, the resolution of the microscope will improve.
- 24What particles are hadrons and what force do they more likely interact with?protons, neutrons and other particles with larger rest mass.
Thy act predominantly through the strong nuclear force. - 25What are the difference between fermions and bosons?Fermions are building blocks of matter. They have half-integral spins, can only occupy 1 per state (Pauli exclusion principle) and include particles such as electrons, protons, neutrons, quarks and neutrinos
Bosons carry forces over distances. They have integral spins, many occupy the same state and include particles such as photons, 4He atoms and glueons - 26what properties did physicists believe fundamental particles and how did they believe it could be explained?Magnetic properties, due to observations about how they behaved when absorbing or emitting light.
It could be explained if the particles could be thought to spin around their own axis - 27Explain the spin of fundamental particles What can the spin be thought of as?Since it is a quantum number, the spin can only have discrete values and represent a fraction of Planck's constant, divided 2π so
h/2π
e.g. an electron has a spin of 1/2 and can only have a spin of this amount.
The spin can be thought as angular momentum, so an electron has an angular moment of 1/2 * (h/2π)
which is written as 1/2 for short. - 28What are the carriers of force?They can be thought of as the agents that cause the fundamental forces in nature.
Photons mediate the EM force
W+, W0 and Z bosons mediate the weak nuclear force
Gluons mediate the strong nuclear force
Gravitons mediate the gravitational force - 29How do photons mediate the electromagnetic force?Photons that are ejected from charged particles can exert forces on other charged particles, causing electric force.
- 30What is the graviton thought to do?Transmit information and cause gravitational force.
- 31Why can bosons be called messenger particles?Bosons carry information about the magnitude and direction of a force over a distance, so in a sense, they do carry messages (but do so much more)
- 32—
Información
- Descripción
- Fichas sobre Sin título, creado por Alex Obray el 21/04/2016.
- Creado por
- Alex Obray
- Visitas
- 0
- Valoración