Investigating the Capacitance of a Parallel-Plate Capacitor Using a Reed Switch
Date: 25th March, 2010
Title: Investigating the capacitance of a parallel-plate capacitor using a reed switch
Objective: To investigate the factors which affect the capacitance of a parallel-plate capacitor using a reed switch.
Apparatus:
- reed switch - signal generator - capacitor plates of area about 0.24m X 0.24 m 1 pair - polythene spacers ( 10 X 10 X 1 mm ) - polythene sheet, same area as capacitor plate 1 mm thick - battery box with 4 cells 2 - voltmeter - light-beam galvanometer - standard mass, e.g. 100g - resistance substation box - CRO - Connecting leads
Procedure:
The reed switch 1) The reed switch was examined. The plastic box was opened up and looked inside. 2) The yellow terminals of the reed switch module were connected to low impedance input of a signal generator. The frequency was gradually increased. If necessary, the voltage output was increased. 3) Note that a diode was connected in series to the coil inside the module.
Setting up the apparatus
4) The apparatus was set up as above. The capacitor plates were separated with 4 polythene spacers placed at the corners. The frequency and voltage of the signal generator were adjusted such that a sound was heard and the spot in the light-beam galvanometer was deflected. 5) When a signal of frequency f was applied, X vibrated between Y and Z at the same frequency. When X made contact with Y, the capacitor was charged by the d.c. supply: when X made contact with Z, it discharged through the light-beam galvanometer. 6) An essential condition for which I=Qf was stated. 7) A variable resistor was connected in series with the galvanometer to protect it from damage. Damage may result from an accidental connection of the d.c. supply to the galvanometer. 8) If the resistance was too low, it had little effect. If it was too high, the discharge of the capacitor may be incomplete. A CRO was connected across
Title: Investigating the capacitance of a parallel-plate capacitor using a reed switch
Objective: To investigate the factors which affect the capacitance of a parallel-plate capacitor using a reed switch.
Apparatus:
- reed switch - signal generator - capacitor plates of area about 0.24m X 0.24 m 1 pair - polythene spacers ( 10 X 10 X 1 mm ) - polythene sheet, same area as capacitor plate 1 mm thick - battery box with 4 cells 2 - voltmeter - light-beam galvanometer - standard mass, e.g. 100g - resistance substation box - CRO - Connecting leads
Procedure:
The reed switch 1) The reed switch was examined. The plastic box was opened up and looked inside. 2) The yellow terminals of the reed switch module were connected to low impedance input of a signal generator. The frequency was gradually increased. If necessary, the voltage output was increased. 3) Note that a diode was connected in series to the coil inside the module.
Setting up the apparatus
4) The apparatus was set up as above. The capacitor plates were separated with 4 polythene spacers placed at the corners. The frequency and voltage of the signal generator were adjusted such that a sound was heard and the spot in the light-beam galvanometer was deflected. 5) When a signal of frequency f was applied, X vibrated between Y and Z at the same frequency. When X made contact with Y, the capacitor was charged by the d.c. supply: when X made contact with Z, it discharged through the light-beam galvanometer. 6) An essential condition for which I=Qf was stated. 7) A variable resistor was connected in series with the galvanometer to protect it from damage. Damage may result from an accidental connection of the d.c. supply to the galvanometer. 8) If the resistance was too low, it had little effect. If it was too high, the discharge of the capacitor may be incomplete. A CRO was connected across