Physics 20 Test 4 Essay Questions

Which way do electrons behave?

As both waves and particles!

What is the general relationship between the frequency of EM radiation, and the energy of the EM radiation? What is the general relationship between the frequency of EM radiation, and the wavelength of the EM radiation? To state your point clearly, compare The IR and UV regions of the spectrum.

As frequency increases, energy also increases. As frequency increases, wavelength decreases. Ultraviolet light has a higher frequency and higher energy then Infrared light, but a shorter wavelength.

In the case of a simple refracting telescope, what is the nature of the two lenses and their spacing?

Two convex lenses, set so that the rays of light converge on the focal point of the the objective lens.

When sound waves alternately interfere, constructively and destructively, we hear a sound that varies from loud to quiet. What happens when light waves interfere?

We see bright spots and dark spots.

What is "The Electromagnetic Spectrum"? Name as many regions of the spectrum as you can.

the distribution of electromagnetic radiation according to frequency or wavelength. Radio, microwave, infrared, visible, ultraviolet, X-Rays, Gamma Rays.

When things interact to produce patterns of constructive and destructive interference, these things are behaving as _________.

waves

Draw a diagram of a hydrogen atom, for the case of the electron in the n=3 state.

*add two more orbits.

What is the range of wavelengths for visible light?

400 - 700 nm

Describe "Huygens' Principle". Show how one plane wave propagates to form a new plane wave.

A point source of light is a "wavelet," and they produce circular "wave fronts."

Almost a century later, experiments such as: (1) Compton scattering and (2) the photoelectric effect confirmed Newton's point of view. Pick one of these two experiments and describe it in greater detail.

(1) When an incoming photon collides with an electron, both the photon and the electron scatter away from the direction of collision at congruent angles, acting like billiard balls, and the scattered photon has a slightly longer wavelength.

What type of lens should be used to correct the vision defect known as myopia (or nearsightedness)? Explain why.

A diverging lens, because it will diverge light before it reaches the eye.

What is the meaning of a transparent material's "index of refraction" (also referred to as "optical density")?

A measure of the way in which transparent materials refract beams of light.

What is the resulting pattern when monochromatic light passes through two closelyspaced, narrow slits (Young's Double-Slit Experiment)? Why is this the pattern? What must be true of the size of the slits and their spacing, in comparison to the wavelength of the light?

A series of alternating bright and dark spots. Because the light waves alternately interfere constructively and destructively. ?????? They must be very small and very closely spaced together. ????????

Distinguish between the three types of ionizing radiation (alpha, beta, and gamma).

Alpha: Two neutrons & two protons; positive charge; slowest; poor penetration; little deflection in mag. field. Beta: Fast moving electrons; negative charge; almost the speed of light; good penetration; greatest deflection in mag. field. Gamma: a form of energy; neutral; speed of light; very good penetration; no deflection in mag. field.

There are two major classifications of nuclear bombs. How is a hydrogen bomb different from an atomic bomb?

Atomic bombs are made of two sub-critical pieces that are driven together (fission), while hydrogen bombs get energy from the fusion of two lighter nuclei.

Why is Neils Bohr's model of the hydrogen atom referred to as a "quantum model"?

B/c his model claimed that electrons travel only in certain orbits around the atomic nucleus, and the atom emits light when electrons make "quantum jumps" from one orbit to another.

Why is the sky blue?

Because Rayleigh Scattering scatters light with the shortest wavelengths the most, and our eyes are trained to pick up blue over violet light.

What type of lens is a magnifying glass (converging, or diverging)? Are the images produced by such a lens: always real, always virtual, or possibly both? Are the images produced by such a lens: always magnified, always reduced, or possibly both?

Converging. Can form both real and virtual images. Can both magnify and reduce images.

What is the role of control rods, in nuclear reactors? What is the role of materials known as moderators, in nuclear reactors?

Control rods control the fission rate of uranium and plutonium. Moderators reduce the speed of fast neutrons, allowing them to sustain a nuclear chain reaction.

What is phosphorescence? Give an example where phosphorescent materials are used in everyday life.

Fluorescence with a time delay. EX: Anything that is glow-in-the-dark.

Give one example of a beneficial use of ionizing radiation.

Gamma radiation kills cancer cells by damaging their DNA.

What does the graph above tell us about the stable isotopes of heavy elements compared to the stable isotopes of lighter elements?

Heavy elements have relatively more neutrons than lighter elements.

Refraction occurs when light passes through transparent materials. Light travels at different speeds in all different transparent materials. State a general rule about the direction a ray of light bends, when it travels across the boundary of two materials with different speeds of light.

If a ray of light passes from a fast (less dense) material into a slow (more dense) material, it will bend towards the normal. If a ray of light passes from a slow material into a fast material, it will bend away from the normal.

What is the difference in the emission spectrum for: (1) an incandescent bulb vs. (2) an excited gas tube of one single element (such as hydrogen, sodium, or mercury gas)?

Incandescent bulbs emit the entire spectrum of visible light, whereas excited gas tubes of a single element only emit certain wavelengths of visible light.

Carbon-14 is an unstable isotope of carbon, with a half-life of 5,730 years. What role does carbon-14 play in the dating of fossilized, organic matter? What is the upper limit to the effectiveness of radiometric carbon dating?

It allows scientists to date objects that are less than 50,000 years old, based off the amount of carbon that remains in them.

Estimate the half-life of the unknown sample based on the graph below (show your calculation):

It takes approximately 25 days for the radioactivity count to go from 14000 to 7000, so the half life of this sample is about 25 days.

What did Robert Millikan determine regarding the electron? What were some of the key ingredients for his experimental apparatus?

Its size. Two charged plates, a battery, a microscope, an atomizer, and a drop of oil.

In the 1600's, Isaac Newton and Christian Huygens had different viewpoints on the nature of light. What was the difference?

Newton said light was a particle, while Huygens claimed it was a wave.

How is nuclear fission different from natural transmutation? What role do high-speed neutrons play in nuclear fission?

Nuclear fission is when an atom nucleus splits into two smaller atoms. Natural transmutation is when an atomic nucleus becomes a different type of atom nucleus through either adding another atom to it or by splitting it. High speed neutrons are what causes the atomic nucleus to split.

What does the graph above tell us about nuclear fission vs. nuclear fusion?

Nuclear fusion occurs between atoms lighter than iron; nuclear fission occurs with atoms heavier than iron.

Explain the difference between real images and virtual images.

Real Images: Images that can be projected onto a screen. Can only be formed by convex lenses. Virtual Images: Images that can only be seen by looking through the lens. Can be formed by both convex and concave lenses.

What are the three "primary colors" for the addition of light? What happens to each these three individual colors when white light shines on a ripe banana?

Red, green, & blue. Red light and green light are reflected, blue light is absorbed.

What did Ernest Rutherford discover about the nature of matter? What were some of the key ingredients for his experimental apparatus?

That matter is mostly empty space. Gold foil, a vacuum, a scintillation viewer, and an alpha particle source.

How does our Sun continually provide energy for us? What is the link between the famous equation E = mc^2, and our Sun?

The Sun produces energy by the nuclear fusion of hydrogen into helium in its core. The sun uses nuclear fusion to convert mass to energy by the formula E=mc^2.

A ray of light usually undergoes a little bit of reflection and a little bit of refraction when it strikes the boundary between two transparent materials. For transparent materials, what condition must be satisfied, so that the ray of light only reflects, and none if it refracts? What is the name of this phenomenon? What is one practical application of this phenomenon?

The angle of incidence must be greater than the critical angle. Total Internal Reflection. EX: Fiber optic cables used for surgery.

What is the "Law of Reflection"? How is specular reflection different from diffuse reflection?

The angle of reflection is equal to the the angle of incidence. Specular: light rays reflect off a smooth surface and remain concentrated in a bundle upon leaving the surface. (can create a reflected image.) Diffuse: light rays reflect off a rough surface and diffuse in many different directions. (cannot create a reflected image.)

Why are large nuclei unstable? What two forces must be balanced, in order for a nucleus to hold together?

The distance between nucleons is big, and so the strong nuclear force between them becomes weak. The electric repulsion and the strong nuclear force.

What is fluorescence? What analogy can be made between fluorescent materials and a staircase?

The emission of light by a substance that has absorbed light or other electromagnetic radiation. You can jump up a staircase, and then slowly descend the steps one at a time.

What is dispersion? Give an example of a typical case where you could see white light being dispersed.

The separation of white light into all the colors of the rainbow due to refraction at extreme angles. EX: light being shone through a triangular prism, and creating a rainbow.

What is the definition of half-life, as it relates to unstable isotopes?

The time required for half of the nuclei in a sample of a specific isotope to undergo radioactive decay.

Uranium-235 and Uranium-238 are both naturally occurring isotopes, found in the earth's crust. Give at least 2 key differences between U-235 and U-238.

There is only one U-235 isotope for every 140 U-238 isotopes. 235 splits, 238 absorbs.

What is the advantage of LED light bulbs over incandescent light bulbs, for household use?

Unlike incandescent bulbs, LED bulbs waste practically no energy as heat, allowing less energy to be used to produce the same amount of light.

What is the name given to the region of the EM spectrum, that we detect with our eyes?

Visible light.

What is on the x-axis and the y-axis of this mass converted to energy graph?

X-axis: # of protons Y-axis: mass per nucleon

What is on the x-axis and the y-axis of this exponential growth graph?

X-axis: #of protons Y-axis: # of neutrons

What experiment was performed in the early 1800's that confirmed Huygens' point of view?

Young's Double Slit Experiment.

There is something special about each of the following elements, as it relates to their nuclei. For each of the following elements, give its atomic number, and what is special about it. Be as detailed as possible in your descriptions. a) Hydrogen b) Helium c) Iron d) Lead e) Uranium

a) 1; most abundant element in the universe b) 2; ???????? c) 26; heaviest element made in a typical star d) 82; heaviest stable isotope. e) 92; largest naturally occurring element.

What did Louis de Broglie hypothesize, based on the results of several experiments performed by others in the early 1900's?

all matter displays the wave-particle duality of photons

Of the following quantities, which are quantized, and which are not: (1) electric charge, (2) time, (3) mass (or matter)

electric charge and mass are quantized, time is not quantized.

What is excitation and de-excitation? How are these processes related to the orbit of an electron in an atom? Which process produces light?

excitation: when an electron absorbs a photon and jumps up to a higher, unstable energy level. (Orbit gets bigger.) de-excitation: when an electron emits a photon and jumps back down to a lower, more stable energy level. (Orbit gets smaller.) Light is produced when de-excitation occurs.

When things interact and exchange momentum, these things are behaving as _______.

particles