Physics end Flashcards

Question

Describe and express with units:magnetic flux-

Answer 1

Is a measure of the number magnetic field lines passing through an area. Being the product of magnetic field strength B and the area A. Flux=BAcos(theta)Where theta is the angles between the area and a line normal to the magnetic field.The units for magnetic flux is the Weber (Wb)

Answer 2

cm^2 -\> x10^-4 -\> m^2mm^2-\> x10^ -6 -\> m^2mm^2 -\> x10^-2 -\> cm^2km^2 -\> x10^-6 -\> m^2

Answer 3

A changing magnetic flux induces a potential difference in a conductor.This induced emf (electromotive force) causes a current to flow. Electrons in the conductor are forced to move given by F=qvB sin(theta). This causes one end of the conductor to become more negative or positive.

Answer 4

The induced emf is equal to the rate of change of the magnetic flux.e=Change in flux / change in timeThe SI unit of emf is the volt (V)This may be continued to a situation where there are several loops, giving the equation:emf=(n) Change in flux / change in time.

Answer 5

For a changing areaemf= (n) (B) (A2-A1)/ change in timeFor a changing magnitude of magnetic field strength.emf=(n) (A) (B2-B1)/ Change in time

Answer 6

Lenz’s Law states that the induced emf creates a current in a direction that opposes the change in magnetic flux. This may occur through the motion of a magnet and a solenoid, causing the poles to reverse depending on the motion of a magnet, to repel or attract the magnet in motion.

Answer 7

If the induced poles of the solenoid were to be opposite, then, the magnetic force of attraction between the two unlike poles would cause the magnet to accelerate towards the solenoid. Inducing a greater current in the solenoid, the magnet would further accelerate. This would continue to speed up, increasing the kinetic energy. The energy created would violate the law of conservation of energy. The induced current must therefore flow in a direction to oppose the change in magnetic flux.

Answer 8

Is the current induced in little swirls on a large solid conductor due to a changing magnetic field. These occur in accordance with Lenz’s law so that they have a direction that will flow to oppose the change in magnetic flux.

Answer 9

A generator uses a fixed magnet to generate emfs in rotating conducting loops for electricity production. A generator therefore converts rotational mechanical energy into electrical energy.

Answer 10

To avoid large eddy currents being produced in a solid conductor, slits can be cut into the metal.

Answer 11

Allow generated voltages to be either increased or decreased before they are used. This is done through primary and secondary coils, each coil with it’s own number of loops. Given the relationship:VpNs=VsNpThese are wrapped around an iron core to increase the strength of the magnetic field. Since the same magnetic flux is passing through both coils, the emf for both are the same. Given that the number of loops vary, then the potential difference will change, changing the volts.Though energy is conserved, so it is transferred from current.

Answer 12

A step up transformer.When the number of coils in the secondary coil is greater than the primary. Resulting in a greater potential difference in the secondary coil, increasing voltage. The output current is lower than the input currentA step down transformer.When the number of coils in the secondary coil is lesser than the primary. Resulting in a lesser potential difference in the secondary coil, decreasing voltage. The output current is greater than the input current.

Answer 13

Used to create medical isotopes or in the industry.Isotopes have short half lives, thus they need to be kept in the hospital where they will be used, so that the isotopes do not decay before used. If there was not a readily available cyclotron, then the isotope would have to be made elsewhere and transported. The time would require more of the isotope to be made to compensate for the radioactive decay.Having cyclotron on site reduces costs and increases the number of scans available to patients in time. Some isotopes have short half lives, making them impractical to ship

Answer 14

Magnets: Produce a uniform magnetic fieldIron core: A soft iron that serves to maximise the magnetic field. It is usually laminated to reduce effect of eddy currents which are bad.Rotator coils: Loops of wire around the iron core. A current is induced in the rotor coils as they rotate in the magnetic field.Split ring communicator: 2 metal half rings connect either end of coils to brushes. Brushes: 2 blocks on either side of communicator. Provide electrical contact to an external circuit.Axle: A rod passing through iron core and coils to provide an axis or rotation for the rotator coils.AC: Induced current is not reversed every half rotation of the coils.DC: Induced current is reversed every half rotation of the coils.

Answer 15

This is to keep the current low, as some energy is lost to the surroundings as heat due to resistance. To minimise the energy loss, the current is kept low by using a high transmission voltage.

Answer 16

Identify the key pointsExplain the points relation to physicsImpact on society

Answer 17

Charged particles are accelerated by a uniform electric field in the. The electric field does work on the ions and transfers kinetic energy to the ions (W=qV=Ek=(mV^2)/2).The uniform magnetic field causes the charged particles to move in a circular path so that they return to the electric field by providing centripetal acceleration. The current passing through each dee, alternates, reversing the electric field before the particle returns, accelerating it further.

Answer 18

Conductors convert electric current into EM radiation and vice versa by alternating current, causing oscillating electrons which oscillate an electric field, producing oscillating magnetic field perpendicular. Frequency of continually reproducing waves equals that of oscillation of electrons.

Answer 19

Electrons in receiving antenna is forced to oscillate by electric field of radio wave, they will oscillate in same frequency as electric field. Producing alternating potential difference in receiver.Force (F=Eq)

Answer 20

Must be in same plane of polarisation of radio or television waves, or parallel to the producing antenna.

Answer 21

are transverse waves made up of mutually perpendicular, oscillating electric and magnetic fields which continually reproduce from eachother.

Answer 22

Oscillating charges produce electromagnetic waves of the same frequency as the oscillation

Answer 23

is light composed of a single frequency with waves that radiate in all directions away from the sourcewave sources that maintain a constant phase relationship with each other, having the same frequency.

Answer 24

Sources are in phase if they emit transverse (light) waves with crests or troughs simultaneously. They are out of phase if they emit waves half a wavelength out of step (lander/2)

Answer 25

Light produced through heating, causes electrons to vibrate randomly with a range of frequencies. Light released is composed of several colours of light, thus does not maintain constant phase.

Answer 26

When two or more electromagnetic waves overlap, the resultant electric and magnetic fields at a point are the vector sum of their separate fields.When the waves at a point are in phase, ‘constructive interference’ occurs.

Answer 27

constructively interfere when the path difference from the sources to the point is mLanderdestructively interfere when the path difference from the sources to the point is (m+½)Lander

Answer 28

Bending of a wave as it passes through an opening or an obstacle

Answer 29

Will give bright and dark fringes, constructive and destructive interference. Distance between bright is fringe separation (delta Y), distance between slits is d, distance between wall is L, path difference is excess length.

Answer 30

Monochromatic light passes through slits, from source or single slit. Acting as coherent light source. Diffraction occurs, producing wave pattern visible on wall

Answer 31

Diffraction causes direction of light to bend and disperse like a wave. Thus resulting in a spread of monochromatic light on wall from 2 sources. May arrive in-phase or not because of path difference where they overlap.

Answer 32

Wave pattern with central maxima, propagate outwards with lander distance (mlander)

Answer 33

Maxima on each order, highest intensity on central maxima/0th order, decreased intensity / larger spread on larger orders.

Answer 34

Light passes through many slits, center will maxima as it constructively interferes. Many slits means there will always be two which light is ½ lander out of phase, adjacent slits slightly out of phase. Until path difference increases to one wavelength where maximum occurs.

Answer 35

Path difference = dsin(theta) [trig]mLander gives path difference for mth order.

Answer 36

Angle of 90 substituted for theta gives max m, rounded down.

Answer 37

Light source goes through grating of known d. Angle of 1st order from 0th order is found by using telescope on turntable with grating in centre.

Answer 38

White central maxima. Next orders have violet before red as violet ha smaller wavelength, thus produces maxima at smaller angle. Further orders may have violet overlap with red.

Answer 39

Grating lines are close, meaning maxima viewed at large angles, reducing error in small measurement.Maxima are thin, reduced error in central judgement

Answer 40

Emission of electrons from material that is illuminated with light of sufficiently high frequency. Minimum frequency required is threshold frequency f0

Answer 41

Is the minimum energy required to remove an electron from a surface. This is related to the threshold frequency

Answer 42

Increased f increases max kinetic energy of emitted electrons E=hf (affected by penetration of material).The intensity of the incident light affects the number, but not the energy, of emitted electrons.Below f0, insufficient energy to release least bound surface electrons.

Answer 43

Law of conservation of energy is applied. Energy of photon = Max energy of electron - energy needed to release least bound electronhf=Ekmax - W

Answer 44

produced when electrons that have been accelerated to high speed interact with a target. This interaction causes a sudden change in the direction of motion and speed of the electrons. The decelleration results in kinetic energy converted into EM radiation in the form of X-ray photons.This process has the german name Bremsstrahlung.

Answer 45

a continuous range of frequencies (bremsstrahlung) due to the various proximities of the electrons with the nuclei in the targeta maximum frequency given by where is the potential difference across the X-ray tubehigh-intensity peaks at particular frequencies

Answer 46

Joules / charge e

Answer 47

Photoelectric effect takes place with recorded frequency of lights, electrons travel to anode/detector. Anode charge is increased in negativity until no detection, the potential differnce required is stopping voltage (Vs). Here, work done by electric field = EkmaxW = qDeltaV = eVs = Ekmax

Answer 48

Ekmax = hf - W is related to y = mx + cGradient gives plank’s constant (h)Y intercept is work functionX intercept is threshold frequency

Answer 49

High voltage power supply - generates high potential difference between anode and cathode.Cathode is negative and the Anode is positive. Filament - wire that is heated by low voltage power supply, emits electrons from the cathode to the anode.Target - Small metal plate with very high melting point Electrons strike target to produce X-ray photons.Evacuated Tube - There must be a vacuum (air removed)Cooling System - Prevents target, anode and cathode from overheating. 99% energy transfer is released as heat.

Answer 50

Shows a left skewed graph with high intensity peaks and a maximum frequency. Area is total number of Xray photons.

Answer 51

Accelerating potential (deltaV) works (W) on electrons for kinetic energy. Head on collision results in all Ek becoming Xray energy.W = Ek = qDeltaV = eDeltaV = hfmaxFmax = dDeltaV/h

Answer 52

Attenuation is reduction in intensity as they pass through material due to absorption and scattering of X-ray photons.

Answer 53

Tissue density; higher density tissue produce higher attenuation than lower density tissuesTissue thickness; Thicker bones produce higher attenuation than less thick tissueElements in tissue; Elements with higher atomic number produce greater attenuation.

Answer 54

High photon energy/frequency means highly penetrating(hard) X-rays. Resultant from a high potential difference across X-ray tube. Vise-versa for low

Answer 55

Less exposure means clear image as less movement. Is ideal, thus more intense X-ray beam needed. Meaning more photons, produced by larger filament current.

Answer 56

Wavelength particles have dependant on their momentum.Lander = h/pH = planks constant

Answer 57

They behave like light. With sections bright and dark similar to fringes.

Answer 58

The Davisson Germer experiment shows that an electron beam reflecting off of crystal lattice would not scatter evenly, instead have peaked intensities at angles. dsin=mlander is used to show that lander=h/p is correct.

Answer 59

Range of frequencies of EM radiation emitted/absorbed by matter. 3 types of spectra:Continuous, Line emission (Colour lines), Line absorption (Black lines)

Answer 60

All matter vibrates, charges do so and release EM radiation. Increased temperature, increases oscillations of vibrations, thus frequency of EM, which can result in visible light being emitted.

Answer 61

Increase in temperature will cause higher frequency EM radiation to be released, closer to violet colour.

Answer 62

When atoms of pure gas is heated or subject to potential difference. Light emitted is viewed through spectrometer/diffraction grating, showing color lines on dark.Specific to each gas, thus can identify them.

Answer 63

Emission spectra is specific to each atom as electron shells are different for each. Thus, a known gass’s emission spectra can be used to define its presence via discrete frequencies of light absorbed.

Answer 64

Produced through incident electrons colliding and removing electrons in lower energy levels of target metals. Higher energy level electrons drop down to fill place, releasing X-ray photon with energy equal to the energy difference between the energy levels.

Answer 65

There are different states in an atom, each with their own energy, which can be represented in energy-lvl diagram. Can be raised to excited states through having one electron not in ground state.

Answer 66

From higher to lower, photons are emitted with energy equal to the difference of energy levels the electron passed. Units of energy in eV

Answer 67

the minimum energy required to remove a single electron from the atom in its ground state.

Answer 68

Only one electron with series dependant on ending level from 5 up.Lyman series. N = 1 [UV]Balmer series. N = 2 [Visible]Paschen series. N = 3 [IR]

Answer 69

At room temperature, electron is in ground state, meaning that any transitions that occur will be in the Lymans series, requiring UV light, not visible.

Answer 70

Sun produces white light, spanning the visible spectrum. Electrons in atoms of the suns atmosphere absorb photons with energy equal to the gap between lower/higher energy states. These incident photos are removed from the total light, resulting in the dark lines.

Answer 71

process of converting high-energy photons into a larger number of lower-energy photons

Answer 72

a photon with energy corresponding to a transition from a higher-energy state to a lower-energy state is incident on an atom in the higher state, it can stimulate a transition to the lower state. This results in two identical photons

Answer 73

Stimulated emission occurs when a photon of energy corresponding to a transition of high-\>low energy states is incident on an atom in the energy state, resulting in an incident photon and emitted photon which have equal energy.Spontanious emission results in only one photon release, is also immediate.

Answer 74

A population inversion is required. By having electrons in a metastable state, excited state with longer lifetime. Hence predominating over spontaneous emission.

Answer 75

Within a laser, the grain medium absorbs energy, being excited to a metastable state usually. Eventual population inversion achieved and stimulated emission occurs. Mirrors continually reflect photons, one is partially reflective, allowing monochromatic, coherent, unidirectional light to pass.

Answer 76

Light Amplification by Stimulated Emission of Radiation.Produces intense beam of coherent light

Answer 77

whenever there are more atoms in a higher-energy state than in a lower-energy state. For practical systems, the higher-energy state must be metastable if a population inversion is to be produced.

Answer 78

is coherent and monochromatic, unidirectional and may be of high intensity

Answer 79

Protective eyewear that absorb laser lightProtective gloves reduce burnWarning signs for active laser Electrical safetyFire extinguisher

Answer 80

Describes particles that form fundamental building blocks of matter and forces that govern their behaviour. Fundamental particles are not made of smaller constituentsQuarks, leptons, gauge bosons

Answer 81

Photon - ElectromagneticW, Z - Weak nuclearGluon - Strong NuclearGraviton - Gravitational

Answer 82

particles that are not affected by the strong nuclear force. Electron = e(-) = -1Tau = t(-) = -1Muon = U(-) = -1 And the neutrino equivalent:(Lepton)neutrino = V(lepton) = 0

Answer 83

fractionally charged particles that are affected by all of the fundamental forces, combine to form composite particles and are never directly observed or found in isolation.

Answer 84

Combinations of quarks for Hadrons which are bayrons or mesons. Baryons are formed by 3 quarks that must be all quark or anti quark.

Answer 85

Lepton numbers can be one of three types:· electronic lepton number,· muonic lepton number,· tauonic lepton number,The lepton number, regardless of type, for a lepton is 1. All other particles have a lepton number of 0.Lepton neutrinos have their equivalent lepton number

Answer 86

Quark number is ⅓, anti quark number is -⅓ . All other particles have a baryon number of 0All baryons have number of +1AntiBaryon has number -1

Answer 87

they annihilate, releasing energy according to the mass–energy equivalence formula: E=(delta)mc(squared)

Answer 88

No energy higher than the ground state n=1Energy = Upper state - Lower state