Investigating electric potential between two parallel plates and around a charged sphere using a flame probe
Lam Cheuk Ying Regina
F.6C (12)
Date: 11st March, 2010
Title: Investigating electric potential between two parallel plates and around a charged sphere using a flame probe
Objective: To investigate the vibration of the electric potential with distance using a flame probe
Apparatus:
1 flame probe, 1 goldleaf electroscope, EHT power supply, 1 ray-box, low voltage power 1 pair of capacitor plates, 1 slotted base, 2 polythene tiles, 2 bare copper wire 22 s.w.g. 0.5m, 1 retort stand and clamp, crocodile clips, connecting leads, 1 plastic ball about 0.2m in diameter, coated with a conducting paint and suspended by a nylon thread tied to a small screw on the ball
Procedure:
Calibrating the electroscope
- A piece of tracing paper was fixed on the window of an electroscope and a ray-box was used to cast a shadow of the leaf on it.
- The cap of the electroscope was connected to the + terminal of an EHT power supply and the metal case was connected to the – terminal. The – terminal was earthed.
- The voltage was increased in steps up to about 1500 V and the deflection of the leaf was marked on the tracing paper.
Potential between two parallel plates
- The apparatus was set up as above. The metal plates were placed 0.15 m apart. The EHT supply was adjusted to 1.5 kV. Make sure that the wire which connected the probe and the electroscope did not touch the bench or any earthed conductor.
- The flame probe was lighted. It was moved across the earthed plate to the positive plate and the deflection of the leaf was observed.
- The flame probe was moved in a plane parallel to the metal plates. The deflection of the leaf was observed
- Readings of the distance of the probe from the earthed plate and the potential measured by the probe were taken. The results were tabulated.