#### Transcript Slide 1

```TI-89 Programming
Linear Interpolation Function
How do we find the Needle
Point Gap (in cm) for a
Peak Voltage of 67.3 kV?
Note that as the voltage
increases, the gap length
increases.
How do we find the Temperature of Air at 7,800 feet?
Note that as the altitude increases (+), the temperature
decreases (-)
We use a technique called “linear interpolation”,
in that we assume that the change from one
Table entry to the next is linear.
T2
Tx
T1
h1
h2
h1
hx  h1
 ratio
h2  h1
hx
h2
For a solution, we require five (5) input values:
1. The given lower value
2. The given upper value
3. The “find” lower value
4. The “find” upper value
5. The given table entry value
5 7,800
1
2
3
4
Always be consistent with upper and lower values, so that whether the
entries are ascending or descending, the correct sign will be maintained.
The function program “interp()”
Now a Function Program can be written to take the “five given values” from
the Table as arguments, and return the interpolated value.
Knowing the “ratio” relationship,
a x  a1
 ratio
a2  a1
Develop the equations needed to calculate the interpolated value, and write
the function program to return that value as the output of the function.
Use the examples given to test your function, and solve the assignment.
The Needle Point Gap at 67.3 kV = 8.27 cm.
The standard atmospheric temperature at 7,800 ft = 31.2 oF.
```