version H28986 2014
(c)
the power dissipated in the resistive component of the inductor is governed by the inductive
reactance, which increases with frequency.
Energy Stored by a Capacitor
Apparatus:
Joulemeter/wattmeter
10V d.c. meter instead of 1mA d.c. meter.
Electrolytic capacitor, 1000uF 25V Resistor,
10kΩ (or resistance box) Meter, 10V d.c.
Source of smooth d.c. 0 to 10V 1mA
Procedure:
Charge the capacitor, recording the charging p.d., V
0
and the energy, W
1
, dissipated in the load
resistance, R, by the charging current. Discharge the capacitor through the load and measure the
energy, W
2
, stored by the capacitor. Repeat the procedure for other values of p.d.
Note:
1.
After each discharge, the capacitor terminals should be shorted to remove any residual
charge due to hysteresis in the dielectric.
2.
With the given component values, about 10% of the total energy in both the charge and
discharge processes is dissipated in the input resistance (125kΩ) of the instrument and is not
recorded.
3.
Large electrolytic capacitors are prone to significant leakage. If this proves troublesome, it
is usually possible to reform the dielectric by maintaining the capacitor at its full rated working
voltage until the leakage current falls to an acceptable value.
The wattmeter can be used to investigate the dependence on load resistance of a) time
constant
b) total energy dissipated
Note: the initial current must not exceed the maximum of the range selected.
Energy Stored by an Inductor
Apparatus:
Joulemeter/Wattmeter
Large Iron cored Inductor
10V d.c. meter instead of 1mA d.c. meter.
Source of smooth d.c. 0 - 9V 1mA
Procedure:
Remove the core from the inductor and connect the 17000 and 20000 turn coils in series so that
their inductance is minimised.
Measure the energy, W
1
supplied to the load in 40s and record the current, I
0
Replace the coils on the core to give the same resistance, R, but maximum inductance, L. Ensure
that the pole faces are clean and accurately fitted.
Without changing the supply p.d., Vo, measure the energy, W
2
supplied in 40s.
The maximum current should be the same as before.
Repeat the procedure for other values of current.
