Excel allows you to apply names to arrays, which will make calculations on a *series* of data easier to understand as well.

Worksheet 03y contains a similar internal energy calculation as we’ve seen the last few sections. Instead of calculating the internal energy for one final pressure, this worksheet is set up for calculations using a series of final pressures. For reference, the formula used for this calculation is:

First, add names to each of the input cells using the name box – **V**, **P_1** and **k** for the volume, initial pressure and the constant k, respectively.

To assign a name to the array of final pressure values, **select **the entire range. Enter **P_2 **in the name box. This name won’t appear if you select a single cell in the range, only if you select the entire range.

To calculate the change in internal energy, we’ll use an array formula. Remember, for an array formula, you must first **select all the output cells**. Go to the **formula bar** and enter the formula:

**=V*(P_2-P_1)/(k-1)**

You’ll see that the entire range of values for the final pressure is selected when you type P_2. Note that you’ll get an error if you omit the asterisk.

Because it’s an array formula, use **Ctrl-Shift-Enter **to complete the formula. It will fill the energy column with values. You’ll now have an easy-to-read formula if you click any of the cells in the array.