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Physics 30: Momentum and Impulse

eMATH Activity

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Comparison of Electric and Gravitational Fields

Purpose:

To explore the similarities and differences of electric and gravitational fields exerted by a charged object.

Background:

Any charged object produces an electric field and any mass produces a gravitational field. These fields share some similarities, but are different as well.  The purpose of this eMATH is to explore these fields using two subatomic particles: the proton and an electron.

The following illustration is not to scale but compares proton and electron charge and mass.

Instructions:

1. Download and open the accompanying Excel spreadsheet.

This spreadsheet will be used to compute electrostatic and gravitational fields for any charged object as a function of the distance from the object.
2.

Choose a proton or electron to use in your calculations. In cell C4 enter its charge, and in cell C5 enter its mass.
3. Enter 10 separation distances into the table in the spreadsheet. Be sure to use even increments of separation.  Do not start with zero, as this is not a valid distance from the object.  For example, you could enter 5 to 50 m in increments of 5 m. Note the shape of the gravitational and electrostatic field graphs created by this particle.
4. Enter a new set of separation distances. Be sure to use even increments of separation and remember not to start with zero. Note the shape of the gravitational and electrostatic field graphs again. Pay special attention to the shape of these graphs compared to the ones in step 3.
5. Finally, enter a value of 1.0 into both the charge and mass cells for the particle.  Look at the values of the gravitational electrostatic fields in the table.  Pick any row of values and divide the electrostatic field by the gravitational field.  The result is the ratio of the electrostatic field compared to the gravitational field for this particle.  Make a note of this ratio.
6. Repeat step 4 using the field values from any other row.  Make a note of the ratio determined for these field values.

Analysis:

1.

How do the shapes of the graphs compare between the gravitational and electrostatic fields?
2. Which field is larger for any separation distance?
3. How did the ratios of the electrostatic field to gravitational field in steps 4 and 5 compare?
4. What can you say about the magnitude of the electrostatic field in comparison to the gravitational field for any particle?
5.

A hydrogen atom is simply a proton and an electron.  Both gravitational and electrostatic fields are present in the atom.  Explain which field results in a larger force on the electron in the atom.
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