Web or In-Class Exercises

This is a collection of exercises to be carried out on the web or on the classroom computers. Their intent is to show you a range of numerical answers associated with different physical phenomena; these are the type of calculations which are carried out in the problem-solving type physics courses. In the case of these exercises, the actual calculations are done by the computer but it is hoped that the exercises will help you become accustomed to the computer as a tool and a source of information.

You will be informed in class about when exercises are due to be turned in. They will be logged and returned to you. It would be a good idea to work on the exercises as soon as we have covered the material in class so you won't have to do them all in a rush when they are called for.

A link to the exercises may be found in the right-hand column on the Physics 7120 Calendar. Links in the exercises will take you to the calculation in HyperPhysics.

Note about entering numbers in calculations: When you enter a number in one of the calculations in HyperPhysics, you then just click anywhere outside the box to make sure the transaction is complete and the number is taken. If you need to edit the number, it is usually easiest to just double-click in the data entry box. That will turn the field dark, and any number you type will replace the previous number.

Exercise 1: Wave calculation

1. What is the wavelength in meters of the electromagnetic carrier wave transmitted by the radio station WSB AM at 750 kHz? 1 kHz =103 Hz and the speed of light is 3 x 108 m/s.

2. What is the wavelength in meters of the electromagnetic carrier wave transmitted by GSU's WRAS at 88.5 MHz ? 1 MHz = 106 Hz

3. If a sound is produced at the orchestra standard frequency of 440 Hz, at a temperature where the speed of sound is 345 m/s, what is the wavelength of the sound produced?

4. If the limits of human hearing are 20 Hz to 20,000 Hz, what are the sound wavelengths associated with these extremes. You may use 345 m/s for the speed of sound.

Exercise 2: Open air column resonance
1. If a flute constitutes an open air column, how long must the air column be if it is to produce a frequency at middle-C, 261 Hz?

2. An open-ended organ pipe is to be constructed to sound the note A= 55 Hz, one octave above the bottom note on the piano. How long must the air column be?

Exercise 3: Closed air column resonance

1. A clarinet acts as a closed-ended air column. If its bottom note has a frequency of 130 Hz, how long is the column?

2. The ear canal responds most strongly to frequencies around 3700 Hz because that is the lowest resonant frequency of the canal. If the canal acts like a closed-ended cylinder, how long is the ear canal?

3. If the top resonance of the water tube resonance unit is at a column length of 8 cm when a tuning fork of frequency 1024 Hz , what is the corresponding speed of sound?

Exercise 4: Formation of real images
1. If a camera lens has a focal length of f = 5 cm, at what image distance from the lens must the film be placed to form an image of an object which is 500 cm from the lens?

2. If the object is moved closer to the camera lens ( to 100 cm) what is the distance to the film from the lens?

3. If you want to take a picture of a flower at only 20 cm from the lens, what lens-to-film image distance would be required? (This probably would require and extension tube).

4. In a slide projector the slide is placed very close to the focal length of the lens. If you want to project an image 5 meters away from a f=5cm slide projector lens, where would you have to put the slide (object distance)?

Exercise 5: Formation of virtual images

1. If you are looking through a divergine lens of focal length f = -20 cm at an object which is 40 cm away from the lens, at what distance from the lens would the image appear to be?

Exercise 6: More virtual images

If the object distance is smaller than the focal length of  a magnifying lens, then the image will be virtual, on the same side of the lens as the object and further away.

1. If you use a magnifier of focal length f=10 cm to look at an object which is at 5 cm from the lens, where will the image appear to be? What will be the magnification?

2. If you put the object closer to the focal length, at 9 cm from the lens, where will the image be and what is its magnification?

Exercise 7: Atomic Spectra
Radiation of all the types in the electromagnetic spectrum can come from the atoms of different elements. A rough classification of some of the types of radiation by wavelength is:
Infrared   > 750 nm
Visible   400 - 750 nm
Ultraviolet   10-400 nm
Xrays   < 10 nm
(An approximate classification of spectral colors: Violet (380-435nm), Blue(435-500 nm), Cyan (500-520 nm), Green (520-565 nm), Yellow (565- 590 nm), Orange (590-625 nm), Red (625-740 nm).
1. If the electron in a hydrogen atom (Z=1) makes a transition from n=2 to n=1, the wavelength of the radiation will be  _______ nm, which is in the __________ part of the electromagnetic spectrum.
2. If the electron in a hydrogen atom (Z=1) makes a transition from n=3 to n=2, the wavelength of the radiation will be  _______ nm, which is in the __________ part of the electromagnetic spectrum.
1. If the electron in a hydrogen atom (Z=1) makes a transition from n=4 to n=3, the wavelength of the radiation will be  _______ nm, which is in the __________ part of the electromagnetic spectrum.
1. If the electron in a oxygen atom (Z=8) makes a transition from n=2 to n=1, the wavelength of the radiation will be  _______ nm, which is in the __________ part of the electromagnetic spectrum.

Exercise 8: Radioactive half-life
1. If the half-life of a certain radioisotope is 1 year, what fraction of it will remain after 3 years?  _____________
2. For carbon-14 with a half-life of 5730 years, how long will it take to decay to one-tenth of its original activity? _____________
3. Iodine-131 has a half-life of 8 days. If a given contamination is considered tolerable when it has decayed to one-thousandth (0.001) of its original value, how long would that take? _____________
4. Cesium-137, the most insidious of the contaminants released at Chernobyl, has a half-life of 30 years. If it must reduce to one-thousandth of its initial value, how long would that take? _____________

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