1. Specific Gravity*(d)

Specific gravity of a glass is defined as the ratio of the glass density to the density of pure water at 4°C and 101.325kPa (1atm.) pressure. Specific gravity is measured using the buoyancy method prescribed in JIS Z 8807:1976.

2. Relative Permittivity (ε_r)

The relative permittivity,ε_r , is defined by the ratio of the capacitance C/C₀. The capacitance C₀ of a parallel-plate capacitor in a vacuum is given by the following equation:

where V is the potential difference between the plates, Q is the charge on the plates, ε₀ is the
permittivity of vacuum ( = 8.854×10^-12 F/m), A is the area of the plates and d is the distance between the plates.

When an insulator is introduced between the plates of a capacitor, the capacitance increases and its value, C, is given by the following equation:

ε_r in the above equation is called the relative permittivity which can be obtained from the ratio C/C₀.
In this catalog, it is measured at 20°C and at 1MHz by the method specified in JIS C 2141-1978.

3. Volume Resistivity (ρV)

The volume resistance between the two electrodes forming the two opposite sides of a cube with 1cm edges is called the volume resistivity, ρV, or simply the resistivity. In this catalog the volume
resistance, RV (Ω), is measured with D.C.500V by the method specified in JIS C 2141-1978 and the volume resistivity, ρV (Ω, cm), is calculated by the following equation:

where A is the effective area (cm²) of the main electrode of the disklike specimen and d is the thickness (cm) of the specimen. In this catalog, the volume resistivity is measured at 20°C and 200°C and the measured values are expressed in terms of ρV20°C and ρV200°C.

It is measured by the method of applying to JIS C2139:2008.

Optical Glass Permittivity, Volume Resistivity Measurement Example