Question 1

No matter how close or how far Galileo was from his assistant, he always measured roughly the same time in performing the lantern experiment. Just what time was Galileo measuring?

Accepted Answer

Galileo was measuring the combined reaction time of both himself and his assistant. The experiment involved observing a light signal from his assistant and then responding to it, which incorporates both his reaction time and his assistant's.

Question 2

The first experiment in which the speed of light was measured precisely involved:

Accepted Answer

C

Question 3

The first experiment to measure the speed of light accurately was made by the:

Accepted Answer

The first experiment to measure the speed of light accurately was performed by French physicists Fizeau and Foucault in the 19th century.

Question 4

The speed of light:

Accepted Answer

The speed of light can be determined by observing the motions of the moons of Jupiter. This was first done by Danish astronomer Ole Rømer in the late 17th century.

Question 5

Rømer calculated the speed of light by observing the large moons of Jupiter being eclipsed by Jupiter while that planet was at opposition and while it was at superior conjunction. How large is the difference in the Jupiter-Earth distance when Jupiter is at opposition and when it is at superior conjunction?

Accepted Answer

When Jupiter is at opposition, it is on the same side of the Sun as the Earth, and so the Jupiter-Earth distance is at a minimum. When Jupiter is at superior conjunction, it is on the opposite side of the Sun as the Earth, and so the Jupiter-Earth distance is at a maximum.

The difference between the maximum and minimum distances is equal to the diameter of the Earth's orbit around the Sun, which is 2 astronomical units (au) or approximately 300 million kilometers.

Question 6

Earth is about 150,000,000 km from the Sun. How long did it take light to cross Earth's orbit in Rømer's experimental determination of the speed of light?

Accepted Answer

The time taken by light to cross Earth's orbit in Rømer's experiment can be calculated by using the equation:
Speed of light = distance/time
Given: distance = 150,000,000 km
We need to find the time taken, which can be rewritten as:
time = distance/speed of light
In Rømer's experiment, the speed of light was not known, but the time difference between two eclipses of Jupiter's moon, Io, was measured. This time difference was due to the varying distance between Earth and Jupiter as they revolve around the Sun. When Earth is closer to Jupiter, the time difference is shorter, and when Earth is farther away, the time difference is longer.

Rømer found that the time difference was about 11 minutes when Earth was on one side of the Sun and about 16 minutes when Earth was on the opposite side of the Sun. This means that it took light 5 minutes longer to cross Earth's orbit when Earth was on the opposite side of the Sun compared to when it was on the same side.

Therefore, when Earth is on the same side of the Sun as Jupiter, the time taken for light to cross Earth's orbit would be:
time = distance/speed of light = 150,000,000 km / speed of light

When Earth is on the opposite side of the Sun, the time taken for light to cross Earth's orbit would be:
time = (150,000,000 km + diameter of Earth's orbit) / speed of light

The diameter of Earth's orbit is about 2 times the radius of Earth's orbit, which is about 300,000 km. Therefore, the time taken for light to cross Earth's orbit on the opposite side of the Sun would be:
time = (150,000,000 km + 600,000 km) / speed of light
= 150.6 million km / speed of light

From Rømer's measurements, we know that the time difference between the two scenarios is 5 minutes. Therefore:
16 minutes - 11 minutes = 5 minutes

This means that it took light 5 minutes longer to travel the extra distance (600,000 km) when Earth was on the opposite side of the Sun.

Using these equations, we can solve for the speed of light:
150,000,000 km / speed of light - (150,600,000 km / speed of light) = 5 minutes

Simplifying, we get:
(150,000,000 km - 150,600,000 km) / speed of light = 5*60 seconds

Solving for the speed of light, we get:
speed of light = (600,000 km)/(300 seconds)
= 2000 km/s

Finally, we can use the distance of Earth's orbit and the speed of light to calculate the time taken for light to cross Earth's orbit:
time = 300,000 km / 2000 km/s
= 150 seconds or approximately 2.5 minutes

Therefore, the answer is:
D) about 16 minutes

Question 7

Assuming that Uranus was at opposition to Earth when Voyager II sent back its historic (and magnificent) pictures from Uranus in January 1986, how long did those signals take to arrive after transmission by Voyager? The average distance of Neptune from the Sun is about $2871 \times 10^{6} \mathrm{~km}$ .

Accepted Answer

The average distance from Uranus to Earth when at opposition is approximately 2.6 billion km. The speed of light is about 300,000 km/s. The time taken for light to travel this distance is approximately 2 hours and 31 minutes.

Question 8

As of 2018, Voyager 1 is in interstellar space, about 13 billion miles from Earth. How long does it take data transmitted by Voyager 1 to reach the Deep Space Network on Earth?

Accepted Answer

The Deep Space Network on Earth is used to communicate with spacecraft like Voyager 1. The network uses a system of giant antennas scattered across three continents, which allows it to track and communicate with spacecraft throughout their journeys in space. However, the distance between Voyager 1 and Earth means that it takes a significant amount of time for data to travel between the two. In fact, it takes about 19 hours for data transmitted by Voyager 1 to reach the Deep Space Network on Earth.

Question 9

White light passes through a prism and separates into a spectrum of colors. A second prism is placed so that only the green light from the first prism falls upon it. After passing through this second prism the light will be:

Accepted Answer

Since the second prism only allows green light to pass through, all other colors of the spectrum will be blocked. Therefore, the only color of light that will pass through the second prism is green, resulting in green light.

Question 10

The rear brake lights on a car emit white light but are covered with plastic that allows only pure red light to pass through. What color of plastic would the red light have to pass through in order to emerge as green light?

Accepted Answer

The color of light is determined by its wavelength. Red and green light have different wavelengths, and a filter or plastic color can only remove certain wavelengths, not change them. Therefore, it's impossible for any color of plastic to transform pure red light into green light.

Question 11

Light of a single wavelength falls on a screen with two narrow, closely spaced slits. On a second screen, a short distance beyond the first:

Accepted Answer

This phenomenon is known as the double-slit interference pattern. When light passes through the two slits, it diffracts and creates an interference pattern on the second screen. This pattern consists of a series of bright fringes separated by dark spaces. This occurs because the light waves from the two slits interfere constructively and destructively, causing regions of maximum and minimum intensity on the screen.

Question 12

Around 1801, Thomas Young in England showed that light behaves as a wave by:

Accepted Answer

Shining light through two closely spaced slits and observing the resulting pattern of light on a white screen is known as the double-slit experiment, which provided evidence for the wave-like behavior of light.

Question 13

Who was the first person to suggest that light is made of particles?

Accepted Answer

Isaac Newton was the first person to suggest that light is made of particles, which he called "corpuscles." He proposed this theory in his book "Opticks" published in 1704.

Question 14

In order of increasing frequency, some of the colors that the visible spectrum contains are:

Accepted Answer

The correct order of colors by increasing frequency in the visible spectrum is red, yellow, and blue. Red has the lowest frequency, followed by yellow, with blue having a higher frequency than both.

Question 15

The diameter of your finger is 1 or 2 cm. What type of electromagnetic wave has a wavelength this size?

Accepted Answer

Electromagnetic waves with wavelengths of 1-2 cm correspond to the microwave region of the electromagnetic spectrum. Ultraviolet and visible waves have much smaller wavelengths (in the nanometer range), while radio waves have much larger wavelengths (in the meters to kilometers range).

Question 16

How does the frequency at the red end of the visible spectrum compare with the frequency at the blue-violet end of the visible spectrum?

Accepted Answer

The frequency of light is inversely proportional to its wavelength. Red light has a longer wavelength than blue-violet light, so its frequency is lower. The frequency at the red end of the visible spectrum is about half as big as the frequency at the blue-violet end.

Question 17

How does the wavelength at the red end of the visible spectrum compare with the wavelength at the blue-violet end of the visible spectrum?

Accepted Answer

The wavelength at the red end of the visible spectrum is longer than at the blue-violet end, making it about twice as big.

Question 18

What is the wavelength of radio waves from the FM radio station KTYD, which operates at the frequency 99.9 MHz?

Accepted Answer

The wavelength ($\lambda$) of a radio wave can be calculated using the formula $\lambda = \frac{c}{f}$, where $c$ is the speed of light ($3 \times 10^8$ m/s) and $f$ is the frequency. For a frequency of 99.9 MHz (or $99.9 \times 10^6$ Hz), the wavelength is $\lambda = \frac{3 \times 10^8 \text{ m/s}}{99.9 \times 10^6 \text{ Hz}} \approx 3.0 \text{ m}$.

Question 19

Choose the correct sequence of electromagnetic radiations, in order of increasing wavelengths.

Accepted Answer

The correct sequence from shorter to longer wavelengths is: Ultraviolet (UV), Visible, Infrared (IR), and Radio waves.

Question 20

In terms of wavelengths, gamma rays are:

Accepted Answer

Gamma rays have the shortest wavelengths in the electromagnetic spectrum, shorter than X-rays.

Quiz 5: The Nature of Light