PHYS 175 Final Part 2

Each of the spectral lines seen in the eyepiece of a spectroscope is due to

Electrons making transitions from one energy level to another

True or False? Radio wave travels appreciably faster than any sound wave. Explain.

True (Speed of light = 3x108 m/s and speed of sound is 340 m/s)

True or False? Microwaves and ultraviolet light have different wavelengths but travel through space at the same speed.

True (Speed of light can only change when it travels from one medium to another)

In which of these cases will a ripe banana appear black: when illuminated with red, yellow, green, or blue light? Explain.

a ripe banana is subjected to blue light, it appears black. this is because when blue blight hits a yellow object, it is absorbed and there is no reflection which results i the object appearing black

How could you use the spotlights at a play to change the performers' clothes suddenly from yellow to black? Explain.

shinning blue light would make it appear black

Does sound faster through the lower atmosphere or through the upper atmosphere? Explain.

lower atmosphere sound waves need a medium to travel in

Your friend reasons that magenta and yellow paint mixed together will produce red because magenta is a combination of red and blue and yellow is a combination of red and green—and that the color in common is red. Do you agree or disagree, and why?

no he is not correct. when you mix two colors you are performing additive combinination, so adding magenta and yellow would give you white

A particle (or quantum) of light is called a

photon

a flashlight is pointed toward the surface of a pond (index of refraction 1.33). if the angle of incidence is 30 degrees in the air (index refraction of 1.03), what is the angle of refraction?

- n1(sin1) = n2(sin2) -(1.03)(sin30)=1.33(sin2)0.515 = 1.03 (sin2)0.38=sin02sin^ -1(0.38)=22.33

A butterfly at eye level is 20 cm in front of a plane mirror. You are behind the butterfly, 50 cm from the mirror. What is the distance between your eye and the image of the butterfly in the mirror? Explain your answer.

30+20+20 = 70 cm

The Bohr model of the atom is similar to the solar system. A) What part of the atom does the Sun represent and why? B) What part of the atom does the Earth represent and why?

A. The nucleus, because it is in the center. B. Electron, because it revolves around the nucleus like Earth does the sun.

The wavelength of light changes as light goes from one medium to another, while the frequency remains the same. (**Possible presentation question.**) A) Is the wavelength longer or shorter in water than in air? Explain in terms of the equation speed = frequency × wavelength. B) A certain orange light has a wavelength of 600 nm (6 × 10-7 m) in air. What is its wavelength in water, where light travels at 75% of its speed in air?

A. Wavelength becomes shorter as speed increases so as to maintain the proportionality of the equation. If v which is on the left hand side decreases as it enters water, only wavelength, on the right hand side, can change to accommodate the balance as frequency is constant. B. v = λf 0.75v = (0.75λ)f (as f is constant) Hence new λ is 0.75 times the old λ =450 nm

Wheels from a toy cart are rolled from a concrete sidewalk onto the following surfaces: A, a paved driveway; B, a grass lawn; and C, close-cropped grass on a golf-course putting green. Due to slowing, each set of wheels bends at the boundary and is deflected from its initial straight-line course. Rank the surfaces according to the amount each set of wheels bends at the boundary, from greatest amount of bending to least. Explain your answer.

B>C>A

What color do you get when you mix red and cyan paint?

Black

Identical rays of light in air are refracted upon entering three transparent materials: A, water, where the speed of light is 0.75c; B, ethyl alcohol (speed 0.7c); and C, crown glass (speed 0.6c). Rank the materials according to how much the light ray bends toward the normal, from most bending to least bending. Explain your answer.

C, B, A, because the slower the speed of light travelling through something is the more it will reflect and bend.

How can a hydrogen atom, which has only one electron, have so many spectral lines? Explain.

Hydrogen atoms have so many spectral lines because there are many energy states that a single electron can occupy when it is excited

EM Spectrum

In order of Longest wavelength to shortest wavelength - Radio waves - Microwaves - Infrared - Visible Light ~ROY G BIV - ultraviolet - X ray - Gamma

Which has lower frequencies: ultraviolet or infrared?

Infrared

Green light is emitted when electrons in a substance make a particular energy-level transition. If blue light were instead emitted from the same substance, would it correspond to a greater or lesser change of energy in the atom? Explain.

It would correspond to a greater change of energy because blue frequency than green. Since frequency is directly proportional to energy, blue light corresponds to a higher energy level transition.

There is less difference between the speed of light in glass and the speed of light in water than there is between the speed of light in glass and the speed of light in air. Does this mean that a magnifying glass will magnify more or magnify less when it is used under water rather than in air? Explain

Magnification depends on the difference between the refractive index of the lens (glass) and air. More the difference, more the magnification. Less the difference, less the magnification. The refractive index of glass is close to that of as water, therefore the difference between their refractive indices is less. Hence, a magnifying glass will magnify less when it is used underwater.

Which have the longest wavelengths: visible light waves, X-rays, or radio waves

Radio waves

Suppose a radio wave and a sound wave have the same frequency. Which has the longer wavelength? Explain.

Since the speed of radio waves (RW) is much higher than the speed of sound, the wavelength of RWs are much higher.

if the super bowl was broadcasting via a radio frequency in CA (4.8 x 10^6 m away), how long would it take for the sound (330 m/s) to reach your ears from a TV set 5 m away?

T = (4.8 / c) + (5/330) T = (4.8/3 x 10^8) + (5/330) T = 0.015 sec this assumes the speed of light (c) is 3x10^8

Pretend that a person can walk only at a certain pace—no faster, no slower. If you time her uninterrupted walk across a room of known length, you can calculate her walking speed. If, however, she stops momentarily along the way to greet others in the room, the extra time spent in her brief interactions gives an average speed across the room that is less than her walking speed. How do you think this is this similar to light passing through glass? Explain.

These two cases are similar to each other. The conversations the person has can be compared to the movement of light through glass as both of these interactions seem to slow down the respective subjects.

If you fire a bullet through a board, it will slow down inside and emerge at a speed that is less than the speed at which it entered. Does light, then, similarly slow down when it passes through glass and also emerge at a lower speed? Defend your answer.

This isn't similar as light comes out of the medium and returns to its original speed of 3x108. But in the case of the bullet it slows down after it passes through the board. This is because the bullet loses momentum when it passes through the board and slows down because of the inhibition. In the case of light, there is no transfer of momentum.

Which has shorter wavelengths: ultraviolet or infrared?

Ultraviolet

Which has higher frequencies: radio waves or visible light waves?

Visible light waves

using a spectroscope to examine light from an incandescent lamp reveals

a continuous spectrum

UV and IR: A) Describe what ultraviolet and infrared light have in common. B) Describe what ultraviolet and infrared light do NOT have in common. C) Describe why ultraviolet light, but not infrared light, is effective in making certain materials fluoresce. (**Possible presentation question.**)

a) They are both invisible to the naked eye as they lie on either end of the visible spectrum. b) Pretty much everything else, from wavelength, to frequency and every property resulting from this. c) During fluorescence, an EM wave is absorbed and the waves that are later emitted have lower energy (and frequency). When ultra violet light is absorbed, waves of lower energy are emitted Eg. Blue light, green light or red light which are visible to the eye. When infrared light is absorbed, the resulting emission will have a lower energy than infrared. Since infrared light is itself invisible to the human eye, waves of lower energies are invisible too and fluorescence wouldn't be possible.

Rank each of the following from smallest to greatest speed in a vacuum: yellow light, x rays, ultraviolet, microwaves, green light, infrared.

all of the colors will have the same speef as they are a apart of the same electromagnetic wave

Excitation is the process in which

electrons are boosted to higher energy levels in an atom

A spread of colors is called a spectrum.

false a spread of every component of sunlight is called spectrum. This incluses all the colors along with UV, X-ray, gamma, micro, etc)

An opaque object is the color it absorbs

false an opaque object is the color it reflects

An opaque object is the color of white light.

false an opaque object is the color it reflects

The brightest portion of the spectrum of sunlight is violet.

false that would be yellow

Human vision is most sensitive to colors in the red-orange part of the visible spectrum

false we are more sensitive to violet-indego part of the spectrum

Rank each of the following from smallest to greatest wavelength: yellow light, x rays, ultraviolet, microwaves, green light, infrared.

microwaves>infrared>yellow>green>ultraviolet>x rays

An atom that absorbs a photon can then emit one

only at the same or lower energy

When blue light falls upon a material and causes it to fluoresce, the fluorescent color can be

red

The Sun is 1.50 × 10^11 m from Earth. How many minutes does it take the Sun's light to reach Earth? Show all of your work and use the speed of light as 3x10^8 m/s. (**Possible presentation question.**)

s = d/t t = d/s (rearranging the equation) t = (1.5x10^11) / (3 x 10^8)= 500 seconds 500 seconds = (500/60) mins. = 8.3 mins.

In 1676, the Danish astronomer Ole Roemer had one of those "aha" moments in science. He concluded from accumulated observations of eclipses of Jupiter's moon at different times of the year that light must travel at finite speed and needed 1300 s to cross the diameter of Earth's orbit around the Sun. Using 300,000,000 km for the diameter of Earth's orbit, calculate the speed of light based on Roemer's 1300-s estimate. How does it differ from a modern value for the speed of light?

s= d/t s = (3x10^11m)/(1300s) = 2.3 x 10^8 m/s s = 2.3x108 m/s In the 15th century, the technology to measure distance and time were not very accurate, hence, although a great effort by Roemer's, this is inaccurate and differs by 70,000,000 m/s.

More than 200 years later, Albert A. Michelson sent a beam of light from a revolving mirror to a stationary mirror 15 km away. Explain how the time interval between light leaving and returning to the revolving mirror was 0.0001 s. Show all of your work and use the speed of light as 3x10^8 m/s. Recall that 1000 m = 1 km. (**Possible presentation question.**)

s= d/t t = d/s d = 2 x 15000 = 30000 meters (leaves and returns to same place hence 2x distance) s = the speed of light = 3x108 m/s t = 3x104/3x108 = 0.0001 seconds

The nearest star beyond the Sun is Alpha Centauri, 4.2 × 10^16 m away. If we were to receive a radio message from this star today, show that it would have been sent 4.4 years ago. Show all of your work and use the speed of light as 3x108 m/s. Recall that 1000 m = 1 km.

s= d/t t = d/s t = (4.2x10^16)/(3x10^8) = 1.4x108 seconds t = (1.4x10^8 seconds) / ( 3600s x 24hrs x 365 days) {dividing by the total number of seconds in a year) t = 4.4 years.

An opaque object is the color it reflects.

true

A transparent object is the color of the light it transmits.

true a red break light in a car transmits red light

Sunlight is a combination of all colors.

true a spectrum of sunlight reveals all colors

A white object appears when illuminated by white light.

true even if one color is missing it would not be white anymore

An opaque object is the color of the light that shines on it.

true if this phrase means reflect, then it is true

White is not actually a color.

true it is a combination of all colors

Black is not actually a color. (**Possible presentation question.**)

true it is the absence of any color

Does light travel faster through the lower atmosphere or through the upper atmosphere? Explain.

upper atmosphere it is fasted when there are no particles, so since the upper atmosphere has less particles than the lower, it will be faster

What can the human eye see?

visible light

Using your answers from the previous questions, rank each of the following from smallest to greatest frequency: yellow light, x rays, ultraviolet, microwaves, green light, infrared. Explain your answer to the last question using an equation and describe the mathematical relationship between wavelength and frequency.

x rays>ultraviolet>green>yellow>infrared>microwaves c=lamdaf

Using your answer to question 3), rank each of the following from smallest to greatest period: yellow light, x rays, ultraviolet, microwaves, green light, infrared. Explain your answer to the last question using an equation and describe the mathematical relationship between frequency and period.

xray>ultraviolet>green>yellow>infrared>mircowaves t=1/f waves with higher frequency will have lesser time period