DIELECTRIC CONSTANT OF A CAPACITOR Description and Specifications for Lab Tenders
DIELECTRIC CONSTANT OF A CAPACITOR.
DIELECTRIC CONSTANT OF A CAPACITOR The relationship between capacitance C, charge Q and voltage V is described by ratio C=Q/V. The capacitance of a parallel plate capacitor depends on distance “d” between its plates, on area A of plates and on the insulating material between the plates and especially on its dielectric constant. The first test concerns the measurement of charge Q of the capacitor versus voltage V. Consequently, capacitance is determined as slope of Q-vs-V curve. The measurement will be carried out at a fixed distance “d” with different areas of plates, in the second test. Distance can be varied by steps of 1 mm. The variation of distance “d” between plates of constant area A will confirm proportionality Cαa1/d, in the third test. The permittivities of two different dielectrics (polystyrene and glass) between the capacitor plates will be determined in the fourth test. TRAINING PROGRAM • determining the capacitace of a plate capacitor by measuring its charge • measuring capacitance versus the area of plates • measuring capacitance versus the distance between plates • determining the dielectric constant of different materials COMPONENTS • kit of dielectric constant • electrometer amplifier • digital multimeter • flexible cables KIT OF DIELECTRIC CONSTANT It includes a rail with a scale of 0-10 cm printed on a side, 2 wide plates and 2 small plates for capacitor, spacers of PVC, pane of glass and plate of polystyrene, capacitive module. DISASSEMBLABLE CAPACITOR Area of (aluminium) plates : 400 mm2, 800 mm2 Intervals : variable, 1, 2, 3, 4, 6 mm Pane of glass: 21 x 21 cm Plate of polystyrene : 21 x 21 cm ELECROMETER AMPLIFIER Electrometer ampplifier used to measure the charge Input impedance > 1013 Ω Input current ≤0.5 pA Output voltage: up to +10 V Output current: 5 mA Output impedance = 1 Ω Supply voltage: 12 Vac DIGITAL MULTIMETER Resistance range: 200 Ω, 2000 Ω, 20 k Ω, 200 k and 2000 k Ω DC voltage: 200 and 2000 mV 20, 200 and 1000 V AC voltage: 200 and 750 V Direct Current: 200, 2000 μA 20 and 200 mA 10 A