Excel – Superscripts in Excel chart labels

For the line segment, you just choose to plot as a scatter plot, but use a line to connect the points.

For the quadratic, you will need to compute a number of points on your curve and then plot them also as a scatter plot, and again, use a line to connect the points from your minimum X value up to your maximum X value.

Update (for Excel 2007 ... probably similar for other versions, but this is what I have in front of me):

To add an additional plot to your chart:

1. Right click on an empty place in your chart and select "Select Data"
2. Select "Add" from the Series list
3. Optionally, name the series in the Series name textbox ... it will be given a default name if you don't provide one.
4. Click on the Series X data textbox, and select the X values for your scatter plot
5. Click on the Series Y data textbox, and select the Y values corresponding to the X values you just selected
6. Press "OK"

You've asked two different (albeit related) questions here. You should consider splitting this into two separate questions.

In answer to your first:

1. Create your chart as a Scatter (XY) Type.
2. Adjust your axis (for min/max limits) and any other formatting you desire.
3. Select this first chart and choose copy.
4. Paste a copy of your first chart on your worksheet.
5. On your second chart, select your horizontal axis, then choose Format Selection.
6. In the Axis Options window, check the Logarithmic Scale box and enter your Base value (default is 10). Log scales are not available in the basic line chart or area chart options.

You now have two identically formatted charts, showing the same data with the difference in how the horizontal scale is displayed, like this:

In short answer to your second, this is very easy to do in Excel. The simplest method would be to setup a table with your base X values (e.g. as you describe above), a "model cell", and in place of static Y values, you'd have a formula (e.g. X*mod = Y). You would then just plot the Y values, which would change whenever you updated the value in your "model cell". This can get pretty complex and sophisticated with some work (e.g. using a lookup table to preset the "model cell" values, or using contingency tables). But as I started this answer, this is really a second question that requires additional detail from you to properly answer.