Experiment Description

Experiment

Experiment E16    Measuring Reactances of A Capacitor and An Inductor

Objectives
  • Investigate the relationship between r.m.s. current and r.m.s. voltage for a capacitor and for an inductor at a fixed frequency
  • Measure reactance in an a.c. circuit
  • Select the best arrangement of meters when low reactance and high reactance are measured
  • Calculate reactance from a plot of V-I graph
  • Work out capacitance from capacitive reactance
  • Work out inductance from inductive reactance
Description
In this activity, you will measure the reactance in an a.c. circuit using V-A methods with an a.c. voltmeter and an a.c. ammeter. Two types of connections are used to cater for the size of reactances. Both the reactances of capacitor and inductor at 50 Hz would be measured.

In Experiment 1, you will measure the reactance of a capacitor in a way similar to measuring the resistance of a resistor. I.e. using a voltmeter and an ammeter. You will vary the rheostat to control the current. The r.m.s. voltage and r.m.s. current through the capacitor are plotted in a graph to dtermine the reactance of the capacitor.

In Experiment 2, you will measure the reactance of an air-core inductor. Since the reactance of the inductor without soft-iron core is small, you will adopt similar connection of meters as before.

In Experiment 3, you will measure the reactance of an inductor with a soft-iron core. Since the reactance of the inductor with soft-iron core is large, the connection is slightly different than before. You will also change to use a potentiometer and milliammeter.
Apparatus
12 V low voltage power supply [1]
capacitor (1000 mF) [1]
coil (1100-turn) with a soft-iron core [1]
rheostat (0 - 20 ohm) [1]
variable resistor (0 - 5 kOhm) [1]
a.c. voltmeter (1 V, 5 V and 10 V) [1]
a.c. ammeter (10 mA, 50 mA, 100 mA, 1 A, 5 A and 10 A) [1]
Experiment