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# ASTR 101- Solar System Astronomy- for Lab 3 - Spectra

Lab 3 - Spectra

Background: A “blackbody” is a term used to describe an object that emits light based solely on its temperature. In other words, it doesn’t reflect any light. In this lab you will observe the nature of light given off by objects and determine if there is a relationship between an object’s temperature and the light emitted.

· This graph shows intensity (y-axis) vs wavelength (x-axis) for light from an object. This type of graph is called a blackbody or thermal radiation spectrum. See the diagram below for information about the simulation.

· For questions concerning the type of light, refer to the chart below.

Type of Light Wavelength

UV less than 0.400 mm

Visible 0.400 – 0.770 mm

Violet 0.400 – 0.450 mm

Blue 0.450 – 0.495 mm

Green 0.495 – 0.570 mm

Yellow 0.570 – 0.590 mm

Orange 0.590 – 0.620 mm

Red 0.620 – 0.770 mm

Infrared more than 0.770 mm

Part 1

· Set the temperature to 3000 K by moving the slider. This is approximately the temperature of the tungsten filament in an incandescent light bulb which is a good example of a blackbody.

· Zoom in on the vertical axis until the range is from 0 to 4, and leave the horizontal range from 0 to 3. This is the characteristic shape you should look for when adjusting the axis range.

· Select the checkboxes for Graph Values and Labels. The graph value shows wavelength (x-axis) and intensity (y-axis). The peak values are shown by default.

1. Describe the shape of the graph. Is it symmetrical?

The graph is not symmetrical. It is flat at the start under the Ultraviolet from 0 to 0.3. It starts rising from 0.4 to 0.966 under the visible section. It later starts going down at the infrared part from 0.966 to 3.

2. What types of light are emitted by this object?

The object emits infrared, ultraviolent and visible lights

3. Find the peak wavelength and use the chart on page 2 to see where that wavelength falls on the spectrum. (This is the wavelength that will be labeled by default on the x-axis.)

Wavelength: 0.966 Type of light: Infrared

Part 2

· Change the temperature to 7000 K.

· Zoom in on the horizontal axis and zoom out on the vertical axis until you can see the whole graph.

· This spectrum represents a “cool white” LED bulb. (Note: LED bulbs come in a range of colors. An LED does not actually have a blackbody spectrum because its light comes from the movement of electrons, not the bulb’s temperature.)

1. What is the peak wavelength and what type of light is this?

Wavelength: 0.414 Type of light (and color): visible (Purple)

2. Comparing the incandescent bulb (3000 K) and the LED bulb (7000 K), which one produces more light in the visible part of the spectrum?

Incandescent bulb at 3000K produces more light at the visible part of the spectrum that LED bulb.

· Set the temperature to 5800 K. This is approximately the surface temperature of the sun. Zoom out on the vertical axis until you can see the whole graph.

3. What is the peak wavelength produced by the sun? What type of light is this?

Wavelength: 84.46 Type of light (and color): Visible (Light blue)

(Note: We perceive the sun as yellow, due to our atmosphere and the way our eyes work.)

4. What types of light are produced by the sun, according to the graph?

Three types of light, Ultraviolet, visible and infrared.

· Change the vertical axis to 0 – 100 and the horizontal axis to 0 - 3

· Change the temperature to 4000 K.

· Click on the camera icon and change the temperature to 5000 K.

· Click again on the camera icon and change the temperature to 6000 K.

5. The graph now shows spectra from three objects at different temperatures. How are the three lines similar? How are they different?

They are flat at ultraviolet light then rise at visible light and slope downwards at infrared part. The peak of the wavelength and spectrum is different as well as the type of light and color when they are at the peak.

Part 3

Click the eraser to clear the saved graphs. Now you will explore the relationship between peak wavelength and temperature. Use the simulation to determine the peak wavelength at each temperature and use the chart on page 2 to find the type of light.

Temperature (K)

Peak Wavelength (mm)

Type of Light (and color if visible light)

3100 K

0.935

infrared

3700 K

0.783

infrared

4800 K

0.604

Visible (yellow)

5000 K

0.580

Visible (yellow)

6200 K

0.467

Visible (yellow)

8500 K

0.341

ultraviolet

10500 K

0.276

ultraviolet

1. According to your data table, how does the temperature of an object affect its peak wavelength?

The higher the temperature gets the lower the peak of wavelength gets hence increase in temperature reduces the peak wavelength.

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