PHYSICS 3LC - FINAL REVIEW

What does a photometer do?

It converts light into electric current.

What are photons?

Tiny quantized packets of light.

What happens in the photoelectric effect?

Light hits a metal and electrons are emitted.

What should the digital multimeter be set to read?

Voltage

Which of the following DOES NOT describe projection imaging?

Produces images of selected planes or slices of tissue of the patient's body.

Which of the following DOES NOT describe tomographic imaging?

A large volume of the patient's body can be viewed with one image.

An ordinary dental X-ray uses which imaging technique(s)?

Projection

Which of the following is NOT a requirement for a suitable probe beam?

It interacts with a large number of cells

Some wave energy can penetrate and pass through a sample. This is a description of what type of interaction with matter?

Transmission

Which of the following is true for the reflection coefficient for a perfect mirror?

I_r / I_o = 1

How does the flux of light from an isotropic source depend on the distance r from the source?

r^-2

What factors DO NOT affect visual acuity?

- Region of retina image falls upon

- Density of receptors

- Level of illumination

All of the above factors affect visual acuity

Where does the actual 'weld' take place on the retinal, based upon the physiology of the eye?

Pigmented Epithelium

Why is damage to neighboring tissue minimized?

(in the context of using cauterizing instruments and lasers for medical procedures)

Because the laser beam is intense and has very low divergence its energy can be focused onto a small spot.

Which statement is correct?

A desk lamp is a isotropic source. A laser is an isotropic source.

A desk lamp is a collimated source. A laser is an isotropic source.

A desk lamp is a collimated source. A laser is a collimated source.

A desk lamp is an isotropic source. A laser is a collimated source.

None of the above

A desk lamp is an isotropic source. A laser is a collimated source.

How does the flux of light from an collimated source depend on the distance r from the source?

It is a constant independent of distance.

To resolve two point sources, what distribution of cones must occur where the image strikes the retina?

There must be a cone producing less than the full response between two cones that produce the full response.

What factors DO NOT make fiber optics well suited to deliver the laser power?

Stiffness

Which type of sensor is the pH sensor? Why?

Indirect; It uses a reagent that changes its optical properties in response to changes in the material of interest

The length of a fiberscope is mostly limited by what?

Spectral Capacity - how much of the transmitted wavelengths are conveyed

What is the relationship between θ_mirror and the customary angles?

θ_mirror = i

Which of the following describe the characteristics of a bundle of fiber used for image viewing?

Coherent; aligned fiber ends

Which of the following describe the characteristics of a bundle of fiber used for illumination?

Incoherent; no specific alignment of the fiber ends is necessary

What is the relationship between θ_bench and the customary angles?

θ_bench = i+r

Where does the majority of the focusing in the human eye occur?

Air - cornea interface

Where does the focusing in the eye of a fish occur?

The lens

How has the eye accomplished correction for spherical aberrations? Fill in the blanks. The______ is flatter at its___________________ than at its______ ,and the______ is denser in the center and hence refracts more strongly at its core than at its outer layers.

cornea; margin; center; lens

Which of the following statements is correct?

A convex lens has both sides rounded outward causing the light rays to converge towards one another. A concave lens has both sides rounded inward, causing the light rays to diverge away from one another.

A convex lens has both sides rounded outward causing the light rays to converge towards one another. A concave lens has both sides rounded inward, causing the light rays to go parallel to one another.

A convex lens has both sides rounded outward causing the light rays to diverge away from one another. A concave lens has both sides rounded inward, causing the light rays to converge towards one another.

A convex lens has both sides rounded inward causing the light rays to converge towards one another. A concave lens has both sides rounded outward, causing the light rays to diverge away from one another.

None of the above

A convex lens has both sides rounded outward causing the light rays to converge towards one another. A concave lens has both sides rounded inward, causing the light rays to diverge away from one another.

How is the lens able to change its refractive power?

The lens can INCREASE its index of refraction, thus increasing its focusing power.

Referring to last problem, is the image upright, or Inverted?

Inverted (negative magnification)

Blue light is bent more by a prism than orange light. Does blue light or orange light have a larger index of refraction in glass?

Blue

What photon energies are selectively filtered (higher or lower energies) in medical imaging techniques?

Lower

Filter manufacturers sell 'interference filters' that only transmit light within a narrow range of wavelengths. For example, an interference filter exists for use with a HeNe laser that strongly attenuates light at wavelengths other than the red laser wavelength (λ = 632nm). Suppose that in Part 5.2.4 of the experiment you held one of these filters between the prism and the telescope. What would you see?

A red line

Which of the following does NOT help the eye compensate for chromatic aberrations?

The fovea reflects radiation in the yellow region of the spectrum.

What is the similarity between MRI and radiation from a gas lamp?

They are both examples of line radiation.

Why does a gas discharge tube (e.g., a neon light) have a certain color?

The gas radiates only a few discrete wavelengths.

Why is it necessary to collimate the light source before using the prism to disperse the light?

So that the light rays entering the prism are parallel

Why are lower energy photons filtered out in medical x-ray imaging?

They only contribute to the patient exposure to the harmful radiation.

They do not contribute to the image formation.

They are quickly attenuated by tissue and therefore do not penetrate the body well.

All of the above are reasons why these photons are filtered out.

All of the above are reasons why these photons are filtered out.

How can the CT image soft tissues with x-rays?

It measures the x-ray penetration along each ray.

Tissue densities are fed into a computer and viewed as a gray-shaded image.

The beam is rotated around the body section to produce views from many angles.

All of the above contribute to created the CT image of soft tissues with x-rays.

All of the above contribute to created the CT image of soft tissues with x-rays.

When light passes through a slit whose size is comparable to the wavelength of the light, the screen shows which of the following:

bright spots due to constructive interference of light waves, and dark spots due to destructive interference of light waves.

bright and dark spots due to destructive interference of light waves.

bright spots due to destructive interference of light waves, and dark spots due to constructive interference of light waves.

nothing.

bright and dark spots due to constructive interference of light waves.

None of the above.

bright spots due to constructive interference of light waves, and dark spots due to destructive interference of light waves.

What is a diffraction grating?

a large number of equally spaced parallel adjacent slits.

What limits the resolution of the eye under optimal conditions?

Diameter of the pupil

Why are the similarities of cesium to potassium and strontium to calcium important?

They are readily assimilated into the body, INCREASING the amount of radiation damage.

Which of the following safety rules should you follow when working with radioactive substances?

When counting samples, do not stand beside the source.

Wash your hands following the laboratory.

Mouth pipetting, eating, drinking, and smoking are prohibited.

Return all sources to the closed, labeled container handled by your T.A.

All of the above

All of the above

What factors affect the biological half-life?

Mode of intake

Water solubility of material

Size of particle

All of the above affect the biological half-life

All of the above affect the biological half-life

Which of the following cellular properties would make the cell more susceptible to damage by ionizing particles?

Cellular division throughout a major portion of the organisms lifetime.

High rate of mitosis.

Lack of specialization in a cellular developmental sequence.

All of the above would make the cell more susceptible to damage

All of the above would make the cell more susceptible to damage

Which of the following is NOT an example of a type of molecular change within the cell typically leading to cellular damage?

A hydrogen radical and a hydroxyl radical combining to form a water molecule.

Ionization of a water molecule into a hydrogen radical and a hydroxyl radical.

A single strand break in double stranded DNA.

All of the above are examples of molecular change leading to cellular damage

A hydrogen radical and a hydroxyl radical combining to form a water molecule.

In Part 7.2.2 of the experiment, a pair of students measure the signal from a cobalt source for 10 sec and find C = 25 counts. They decide to repeat the measurement, but this time read only C = 20 counts. What is wrong?

Nothing is wrong; there is a certain amount of statistical uncertainty in the measurement

Referring to the previous problem, does the absorption of the Heidbrinkions depend on the atomic charge of the absorber, Z? (Hint: μm is a constant if there is no Z dependence.) Cardboard is mostly hydrocarbons (Z=6), aluminum has Z=13, and lead has a Z of 82.

Yes

Which metastable radionuclides are preferable to other radionuclides for diagnostic imaging in nuclear medicine?

Metastable radionuclides that have already undergone electron-emitting transition.

An alpha cannot penetrate your skin. Once inside the body, however, an alpha source is the most hazardous radiation since it causes the most ionizing events per unit length. There is really only one way a sealed alpha source can hurt you. What is it?

By ingestion.

Fill in the blanks. In the PET technique, detectors record the emission of_________ from active substrates to form a tomographic image of the cross-sectional distribution of tissue concentration.

Gamma rays

How do radioiodine experiments diagnose hyperthyroidism/ hypothyroidism?

A hyperactive thyroid may absorb up to 80a hypoactive thyroid may absorb as little as 15% of 131_I

Fill in the blanks. Lower energy particles can act on an atomic electron for a greater length of time, thus increasing the probability of driving an electron out and causing ionization. Thus_______ _______ are more damaging than ________ _______.

Alpha particles; Gamma rays

Suppose that in Part 8.2.4 a pair of students obtain data measuring the range of gammas in lead using thicknesses of 0, 3, 6, and 9 cm. For 0 cm thickness, they measure 2742 counts; for 3 cm thickness, they measure 638 counts; for the 6 cm thickness, they record 155 counts; and for 9 cm thickness, they record 26 counts. Next, they plot their results on semilog paper. Along the x-axis they plot r x, where x is the thickness. Along the y-axis they plot the number of counts. Because they use semilog paper, this is the same as if they did a linear plot with the y-axis being the logarithm of the number of counts. Then they fit a line through the data, and use the graph to determine the mass absorption coefficient μm . On the graph, the mass absorption coefficient is given by

The negative of the slope of the line

When a wave strikes a new medium, three things can happen: reflection, transmission, and absorption. Consider an echo. Do you think reflection is an important process when sound waves produce an echo?

Yes

When a wave strikes a new medium, three things can happen: reflection, transmission, and absorption. Consider a wave propagates in air and is transmitted through a piece of paper. Does increasing the frequency increase the amplitude of a sound wave transmitted through the piece of paper?

No

An interface between air and some other substance, like tissue or water, strongly scatters ultrasound waves. Which of the following is NOT a consequence of this?

Lungs have high ultrasound attenuation rates.

Images are sharper with higher ultrasound frequencies.

Sound transducers should be carefully coupled to the skin via gel.

All of the above are consequences.

Images are sharper with higher ultrasound frequencies.

In order to form a reflection interface for sound waves, what must be true of the materials on either side of the interface?

They must differ in their acoustic impedance.

In an arrangement such as in Lab Manual Figure 10.1, the attenuators are 8 inches by 11 inches. Referring to the previous problem, compare the wavelength with the size of the attenuator. Do you expect diffraction of sound waves by the attenuators to be important? (Hint: Use the diffraction equation (Equation (6.2)) from the lab manual to compare the wavelength with the size of the attenuator. Use the wavelength that you found in the previous question. Let d=8 inches in Eq. (6.2) and find the angle θ . If the angle θ is large, then diffraction is important. It the angle is small (close to zero), then diffraction is not important.)

Diffraction will be somewhat important.

Fill in the blanks. A reflected ultrasound pulse brings back two kinds of information. The _____ of the reflected pulse relative to that of the incident pulse gives information on the type of interface that produced the reflection. The _____ gives information about the distance between the transducer and the reflecting interface.

amplitude; travel time between when a pulse leaves and when it returns to the transducer;

O>f

Inverted, real image

O<f and i is negative

virtual image

The bigger the wavelength

the smaller the index of refraction

Which color has the biggest lambda?

Red

Which color has the smallest lambda

violet