Mr. Rogers' IB Physics Topics Syllabus 1st Quarter 2nd Quarter 3rd Quarter 4th Quarter IB HL Thermo SL Waves HL Waves Communications EM Waves

Option G: Electromagnetic waves

 Objectives Essential Question: How has an understanding of EM waves changed human existance?

The nature of EM waves and light sources

1. Outline the nature of electromagnetic (EM) waves.

• an oscillating electric charge produces varying electric and magnetic fields.

• transverse waves

• all have the same speed in a vacuum.

1. Describe the different regions of the electromagnetic spectrum. (ref)

• microwave

• infrared

• visible

• ultraviolet

• x-rays

• gamma rays

1. Describe the dispersion of EM waves in terms of the dependence of refractive index on wavelength. The refractive index is a function of wavelength. Passing an EM emission composed of multiple wavelengths through a material will bend the light different amounts and hence separate the various wavelengths.

2. Distinguish between transmission, absorption and scattering of radiation.

3. Discuss examples of the transmission, absorption and scattering of EM radiation.

4. Describe the effect of the Earth’s atmosphere on incident EM radiation.

• transparency--the atmosphere is transparent to most of the microwave and the visible light spectrums

• blue sky--blue light is scattered more by air molecules because it has a shorter wave length than red light

• red sunsets or sunrises--the blue light is scattered into outer space leaving mostly red light.

• ozone layer--blocks much of the ionizing UV light that would otherwise reach the surface.

• increased CO2 in the atmosphere--prevents infrared from radiating into space, thus cooling Earth's surface.

 Essential Question: What has been the effect of lasers on innovations in  art science and technology?

Lasers

1. Explain:

• monochromatic--light with a single wavelength

• coherent--light made up of waves that are in phase with each other

1. Identify laser light as a source of coherent light.

2. Outline the mechanism for the production of laser light. Students should be familiar with the term population inversion.

3. Outline an application of the use of a laser.

• 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, etc.

 Essential Question: How do magnifying glasses work?

Optical instruments

 As applied to a converging (convex) lens, define: principal axis focal point focal length linear magnification--(M) the ratio of the size (height) of the image to that of the object. M = - S1 / S2     = F / (F - S1) angular magnification--the ratio of the angle subtended at the observer's eye by the image to the angle subtended by the object when viewed directly. For a Convex lens, define: power--the reciprocal of the focal length of a lens or curved mirror dioptre--a unit of measurement of optical power = 1 / ( focal length measured in meters). Example: a 4 dioptre lens brings parallel rays of light to focus at 1/4 meters. Construct ray diagrams for convex lens showing  the image.  (see The Effects of an Object's Position On The Image Size and Position for a Double Convex Lens) 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. Distinguish between a real and virtual images. the virtual image is upright the object must be between the lens and focal point Apply the convention “real is positive, virtual is negative” to the thin lens formula. 1 / So + 1 / Si = 1 / F

The simple magnifying glass

1. for the unaided eye define:

• far point--For the normal eye, the far point may be assumed to be at infinity

• near point--as close to the eye as possible without becoming blurry. (Typically assumed to be about 25 cm from the eye.)

1. Derive an expression for the angular magnification of a simple magnifying glass for an image formed at the near point and at infinity. (ref)

The compound microscope and astronomical telescope

1. Construct a ray diagram for a compound microscope (ref) with final image formed close to the near point of the eye (normal adjustment).

2. Students should be familiar with the terms objective lens and eyepiece lens.

3. Construct a ray diagram for an astronomical telescope with the final image at infinity (normal adjustment).

4. State the equation relating angular magnification to the focal lengths of the lenses in an astronomical telescope in normal adjustment.

5. Solve problems involving the compound microscope and the astronomical telescope. Problems can be solved either by scale ray diagrams or by calculation.

6. For a single lens, explain the meaning of:

• spherical aberration--with a spherical lens, the further a parallel ray is from the principle axis, the greater the shorter the focal point. This causes fuzziness in the focus. Reducing aperture size helps by eliminating rays further from the principle axis.

• chromatic aberration--different wave lengths of light are bent different amounts as they pass through a lens, hence there is some separation of colors in the image. Combining a diverging and a converging lens made of two different types of glass helps greatly reduce the problem.

Two-source interference of waves

1. State the conditions necessary to observe interference between two sources.

• coherent--the waves maintain a constant phase angle between them.

• monochromatic--the waves have the same wavelength

1. Explain, by means of the principle of superposition, the interference pattern produced by waves from two coherent point sources. The effect may be illustrated using water waves and sound waves in addition to EM waves.

2. Outline a double-slit experiment for light and draw the intensity distribution of the observed fringe pattern. Note: slit width is small compared to the slit separation so that diffraction effects of a single slit are negligible.

3. Solve problems involving two-source interference.

Diffraction grating

Multiple-slit diffraction

1. Describe the effect on the double-slit intensity distribution of increasing the number of slits.

2. Derive the diffraction grating formula for normal incidence.

3. Outline the use of a diffraction grating to measure wavelengths.

4. Solve problems involving a diffraction grating.

X-rays

1. Outline the experimental arrangement for the production of X-rays.

• X-ray Florescence

• Bremsstrahlung production--high velocity electrons hit a metal target and are abruptly slowed down. The kinetic energy lost by the electrons is emitted as high energy photons (x-rays). These form a continuous distribution of wavelengths skewed to the high side with a single well defined peak.

1. Draw and annotate a typical X-ray spectrum. (see ref)

2. Explain the origins of the features of a characteristic X-ray spectrum.

3. Solve problems involving accelerating potential difference and minimum wavelength.

E = hc/ λ

Where: E = energy of a photon

h = Plank's constant

= 4.14 x 10-16 eVs

c = speed of light in a vacuum

= 3.00 x 10-8 m/s

λ  = wave length

minimum wave length = hc / (accelerating voltage)

 Essential Question: What was the key tool that led to the discovery of DNA's double helix structure?

X-ray diffraction

1. Explain how X-ray diffraction arises from the scattering of X-rays in a crystal.

2. Derive the Bragg scattering equation.

3. Outline how cubic crystals may be used to measure the wavelength of X-rays. (DNA was discovered by means of X-ray diffraction.)

4. Outline how X-rays may be used to determine the structure of crystals.

5. Solve problems involving the Bragg equation.

Thin-film interference

Wedge films

1. Explain the production of interference fringes by a thin air wedge. Students should be familiar with the terms equal inclination and equal thickness.

2. Explain how wedge fringes can be used to measure very small separations.

3. Applications include measurement of the thickness of the tear film on the eye and oil slicks. Describe how thin-film interference is used to test optical flats.

4. Solve problems involving wedge films.

Parallel films

1. State the condition for light to undergo either a phase change of π, or no phase change, on reflection from an interface.

2. Describe how a source of light gives rise to an interference pattern when the light is reflected at both surfaces of a parallel film.

3. Explain the formation of colored fringes when white light is reflected from thin films, such as oil and soap films.

4. Describe the difference between fringes formed by a parallel film and a wedge film. Describe applications of parallel thin films

• design of non-reflecting radar coatings for military aircraft

• measurement of thickness of oil slicks caused by spillage

• design of non-reflecting surfaces for lenses (blooming), solar panels and solar cells.

1. Solve problems involving parallel films including  problems involving the application of thin films.

 Essential Question: A?

 Essential Question: A?

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