Hi Pratibha,
The resistance, R, should be chosen based on your measurement setup. The value of that resistance will determine the range of voltage that you measure while performing the sweep. For example, your oscilloscope or other data recording device (even a voltmeter) will have some limited measurement range. The higher the resistance, the lower the current draw, which means that the voltage range will be lower as well. Generally, it’s better to start with larger values of resistance, and then to decrease it if you find that you want/need larger signal levels.
Hope this is helpful, good luck 🙂