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IB HL Physics Option G Objectives
IB HL Physics Option G Objectives List and answers
47
Physics
01/29/2012

Term
 G.1.1: Outline the nature of electromagnetic (EM) waves.
Definition
 - Oscillating electric charge produces varying electric and magnetic fields- Electromagnetic waves are transverse, have the same speed- Oscillating (SHM) charge produces an electric, which produces a magnetic field that is perpendicular.
Term
 G.1.2: Describe the different regions of the electromagnetic spectrum.
Definition
 - Order of magnitude of the frequencies and wavelengths of different regions- Identify a source for each region.
Term
 G.1.3: Describe what is meant by the dispersion of electromagnetic waves
Definition
 Dispersion - separating of white light into itscomponent colors due to refraction.
Term
 G.1.4: Describe the dispersion of EM waves in terms of the dependence of refractive index on wavelength.
Definition
 - As electromagnetic waves enter a new medium, velocity depends on the frequency of the wave - Each frequency will have a different refractive index in the new medium.
Term
 G.1.5: Distinguish between transmission, absorption and scattering of radiation.
Definition
 Transmission - electromagnetic radiation passing from one medium to anotherAbsorption - Photons are absorbed by materialScattering - Deflection of electromagnetic radiation from original path due to collision with particles of medium.
Term
 G.1.6: Discuss examples of the transmission, absorption and scattering of electro magnetic radiation.
Definition
 - Effect of the Earth’s atmosphere on incident electromagnetic radiationExplanations for:the blue colour of the sky red sunsets or sunrisesthe effect of the ozone layersthe effect of increased CO2 in the atmosphere.
Term
 G.1.7: Explain the terms monochromatic and coherent.
Definition
 Coherent Waves - have a constant phase relationship.Monochromatic Waves - single frequency (wavelength).
Term
 G.1.8: Identify laser light as a source ofcoherent light.
Definition
 Laser light is both coherent and monochromatic.
Term
 G.1.9: Outline the mechanism for theproduction of laser light.
Definition
 - Lower energy level electrons are pumped up to higher energy levels and stimulated to fall to energy levels corresponding to specific frequencies, producing laser light.
Term
 G.1.10: Outline an application of the use of alaser.
Definition
 - Medical applications- Communications- Technology (bar-code scanners, laser disks)- Industry (surveying, welding and machining metals, drilling tiny holes in metals)- Production of CDs reading and writing CDs, DVDs
Term
 G.2.1: Define the terms principal axis,focal point, focal length and linearmagnification as applied to aconverging (convex) lens.
Definition
 Principal axis - Line through the focal point of a lens andthe center of the lensFocal point - Location on the principal axis where parallellight rays converge after passing through the lens.Focal length - Distance between the focal point and thecenter of the lens.
Term
 G.2.2: Define the power of a convex lens andthe dioptre.
Definition
 Power of a converging lens - The reciprocal of the focal length of the lensDioptre - The unit of power for a converging lens: 1 dioptre = 1 m-1
Term
 G.2.3: Define linear magnification.
Definition
 Linear magnification - The ratio of the height of the image to the height of the object.
Term
 G.2.4: Construct ray diagrams to locate theimage formed by a convex lens.
Definition
 - All rays incident on the lens from the object will be focused- The image will be formed even if part of the lens is covered
Term
 G.2.5: Distinguish between a real image anda virtual image.
Definition
 Real image - formed when light rays actually converge on a location and can be projected onto a screenVirtual image - formed by light rays that only appear to converge on a location and cannot be projected onto a screen.
Term
 G.2.6: Apply the convention “real is positive,virtual is negative” to the thin lensformula.
Definition
Term
 G.2.8: Define the terms far point and near point for the unaided eye.
Definition
 For the normal eye, the far point may be assumedto be at infinity and the near point is conventionallytaken as being a point 25 cm from the eye.Near point - Distance between the eye and the nearestobject that can be brought comfortably into focus. “least distance of distinctvision” 2. *Far point Distance between the eye and the furthestobject that can be brought into focus.
Term
 G.2.9: Define angular magnification.
Definition
 Angular magnification - Ratio of the angle the image subtends at the eye to the angle the object subtends at the eye.
Term
 G.2.10: Derive an expression for the angular magnification of a simple magnifying glass for an image formed at the near point and at infinity
Definition
Term
 G.2.11: Construct a ray diagram for a compound microscope with final image formed close to the near point of the eye (normal adjustment).
Definition
 Students should be familiar with the termsobjective lens and eyepiece lens
Term
 G.2.12: Construct a ray diagram for anastronomical telescope with the finalimage at infinity (normal adjustment).
Definition
Term
 G.2.13: State the equation relating angularmagnification to the focal lengthsof the lenses in an astronomicaltelescope in normal adjustment
Definition
Term
 G.2.15: Explain the meaning of sphericalaberration and of chromaticaberration as produced by a singlelens.
Definition
 Chromatic aberration - Rays of different frequencies do not all converge at the same focal point due to dispersion by the lens.Spherical aberration - Rays parallel to the principal axis do not all converge at the focal point.
Term
 G.2.16: Describe how spherical aberration ina lens may be reduced.
Definition
 - the lens can be ground to be slightly non‐spherical to adjust for the circle of least confusion - using different combinations of lenses put together- a stop (an opaque disc with a hole in it) is inserted before the lens so that the aperture size can be adjusted to allow only paraxial rays to enter (this reduces the light intensity and introduces diffraction of light)
Term
 G.2.17: Describe how chromatic aberration ina lens may be reduced.
Definition
 - using an achromatic doublet, made from a converging crown glass lens and a diverging flint glass lens that are adhered together- Since the chromatic aberration of converging and diverging lenses is opposite, a combination of these two lenses will minimize this effect.
Term
 G.3.1: State the conditions necessary toobserve interference between twosources.
Definition
 -they must have the same phase- the phase difference between them must remain constant
Term
 G.3.2: Explain, by means of the principleof superposition, the interferencepattern produced by waves from twocoherent point sources.
Definition
 - When two coherent point sources interfere they produce an interference pattern- The dark lines are areas where the two waves interfere destructively, in between the dark points are areas of maximum amplitude where the waves interfere constructively - When the two waves have both traveled an integer value of wavelengths they interfere constructively (assuming the sources are in phase)- If the two waves have both traveled an integer value plus one half of a wavelength they interfere destructively.
Term
 G.3.3: Outline a double-slit experimentfor light and draw the intensitydistribution of the observed fringepattern.
Definition
 - Slit width must be small when compared to the slit separation so that diffraction effects of a single slit on the pattern are not considered
Term
 G.4.1: Describe the effect on the double-slitintensity distribution of increasing thenumber of slits.
Definition
 when monochromatic light passes through a different number of slits we notice that as the number of slits increases: - the number of observed fringes decreases- the spacing between them increases- the individual fringes become much sharper
Term
 G.4.2: Derive the diffraction grating formulafor normal incidence.
Definition
 - The slits are very small so that they can be consideredto act as point sources - They are also very close together such that d is small (10–6 m)- Each slit becomes a source of circular wave fronts and the waves from each slit will interfere- Consider the light that leaves the slit at an angle θ as shown, the path difference between wave 1 and wave 2 is dsinθ and if this is equal to an integral number of wavelengths then the two waves will interfereconstructively in this direction, similarly wave 2 willinterfere constructively with wave 3 at this angle, and wave 3 with 4 etc., across the whole grating. Hence if we look at the light through a telescope, that is bring it to a focus, then when the telescope makes an angle θ to the grating a bright fringe will be observed. The condition for observing a bright fringe is therefore: dsinθ = nλ
Term
 G.4.3: Outline the use of a diffraction gratingto measure wavelengths.
Definition
 - All elements have their own characteristic spectrum.- An element can be made to emit light either by heating it until it is incandescent or by causing an electric discharge through it when it is in a gaseous state - If laser light is shone through a grating on to a screen, you will see just how sharp and spaced out are the maxima- Measuring the line spacing and the distance of the screen from the laser, the wavelength of the laser can be measured.
Term
 G.5.1: Outline the experimentalarrangement for the production ofX-rays.
Definition
 - A Coolidge tube is sufficient- Intensity and hardness of the X-ray beam are controlled- Electrons “boiled off” at cathode/filament get accelerated by high voltage to anode- At anode, electrons hit metal, and produce X-rays- X-rays proceed through walls of chamber- Details of X-ray spectrum depend on metal, energy of electrons- Very little of electron energy converted to X-rays- Most of energy goes into heating anode
Term
 G.5.2: Draw and annotate a typical X-rayspectrum.
Definition
 Students should be able to identify the continuousand characteristic features of the spectrum and theminimum wavelength limit.
Term
 G.5.3: Explain the origins of the features of acharacteristic X-ray spectrum.
Definition
 An electron which makes a transition from the M ‐shell toa vacancy created in the K ‐shell gives rise to the Kβ line. Ifan incident electron ionizes a target atom by ejecting anL‐shell electron then electron transitions from the M‐shelland N‐shell to fill the vacancy give rise to X‐ray lines calledthe Lα and Lβ. respectively. It is apparent that the wavelengthof the lines in an X‐ray spectrum will be characteristic of aparticular element.
Term
 G.5.5: Explain how X-ray diffraction arisesfrom the scattering of X-rays in acrystal.
Definition
 Each lattice ion (represented by a dot) acts as a source ofsecondary waves. In general as these waves overlap theywill tend to interfere in a random manner. However, thosewaves that are scattered at angles equal to the angle at whichthe X‐rays are incident on the ion, will stand a chance ofreinforcing constructively with another scattered wave.Diffraction of x-rays is caused by the scattering of x-rays inside of a crystal.
Term
 G.5.6: Derive the Bragg scattering equation.
Definition
 he direction of two such waves are shown in Figure 1843by the ray labelled 1 that is scattered by the first layer andby the ray labelled 2 that is scattered by the second layer.Ray 2 travels an extra path difference AB + BC where AB =BC = dsinθ, d being the spacing between adjacent crystallayers and θ the angle between the incident X‐ray and thecrystal layer. The two waves will interfere constructively ifthe path difference between them is an integral number ofwavelengths i.e. 2dsinθ = nλThis equation is known as the Bragg scattering equation
Term
 G.5.7: Outline how cubic crystals may beused to measure the wavelength ofX-rays.
Definition
 Students should be aware of the fact that thestructure of DNA was discovered by means of X-raydiffraction. By assuming a perfect cubic lattice array it is possible topredict the resulting interference pattern produced. After measuring the lattice plane distances with x-rays of a specific wavelength, and by using cubic crystals of a known lattice plane distance, the wavelengths of x-rays can be measured.
Term
 G.5.8: Outline how X-rays may be used todetermine the structure of crystals.
Definition
 Another consequence of Bragg’s work is the branch ofphysics known as X-ray crystallography in which X‐raysof known wavelengths are used to explore the crystalstructure of different elements and compounds. This is aquestion of working back from the diffraction pattern todetermine the crystal structure that would produce sucha pattern. It was in this way that, in 1952, Francis Crickand James Watson unraveled the structure of the DNAmolecule.
Term
 G.6.1: Explain the production of interferencefringes by a thin air wedge.
Definition
 Students should be familiar with the terms equalinclination and equal thickness. When the monochromatic light strikes the glass platesome of it will be reflected down onto the wedge. Someof the light reflected from the wedge will be transmittedthrough the glass plate to the travelling microscope. Asystem of equally spaced parallel fringes (fringes of equalthickness) is observed. The travelling microscope enables the fringe spacing to bemeasured. The fringes can also be observed by the nakedeye.
Term
 G.6.2: Explain how wedge fringes canbe used to measure very smallseparations.
Definition
 Applications include measurement of the thicknessof the tear film on the eye and oil slicks.
Term
 G.6.3: Describe how thin-film interference isused to test optical flats.
Definition
 Wedge films can be used to test optical surfaces for flatness.If a wedge is made of two surfaces one of which is perfectlyplane but the other has irregularities, the observed fringepattern will be irregular in shape. The irregular surfacecan then be re‐polished until the fringes are all completelyparallel and of equal thickness.
Term
 G.6.5: State the condition for light toundergo either a phase change of π,or no phase change, on reflectionfrom an interface.
Definition
 Hence if the path difference is an integralnumber of half‐ wavelengths rays 1 and 2 will reinforcei.e. ray 1 and 2 are in phase. However, rays 3, 5, 7 etc willbe out of phase with rays 2, 4, 6 etc but since ray 2 is moreintense than ray 3 and ray 4 more intense than ray 5, thesepairs will not cancel out so there will be a maximum ofintensity.
Term
 G.6.6: Describe how a source of light givesrise to an interference pattern whenthe light is reflected at both surfacesof a parallel film.
Definition
 Consider light from an extended source incident on a thinfilm. We also consider a wave from one point of the sourcewhose direction is represented by the ray shown. Someof this light will be reflected at A and some transmittedthrough the film where some will again be reflected at B(some will also be transmitted into the air). Some of thelight reflected at B will then be transmitted at C and somereflected and so on.
Term
 G.6.7: State the conditions for constructiveand destructive interference.
Definition
Term
 G.6.8: Explain the formation of colouredfringes when white light is reflectedfrom thin films, such as oil and soapfilms.
Definition
 If white light is shone onto the film then we can see whywe get multi‐coloured fringes since a series of maxima andminima will be formed for each wavelength present in thewhite light. However, when viewed at normal incidence,it is possible that only light of one colour will under goconstructive interference and the film will take on thiscolour.
Term
 G.6.9: the difference betweenfringes formed by a parallel film and awedge film.
Definition
 comparison between fringes formeD bya parallel film anD tHose formeD by aweDge film. For a parallel film, the fringes are of equal inclination, thatis they form arcs of a circle whose centre is located at theend of a perpendicular drawn from the eye to the surfaceof the film. For a wedge film, the fringes are parallel and of equalthickness.
Term
 G.6.10: Describe applications of parallel thinfilms.
Definition
 Applications should include: design of non-reflecting radar coatings formilitary aircraft measurement of thickness of oil slicks caused byspillage design of non-reflecting surfaces for lenses(blooming), solar panels and solar cells.
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