B7, General Physics Experiment II c Fall Semester, 2020 Name: Team No. : Department: Date : Student ID: Lecturer’s Signature : Introduction Goals Measure the permittivity constant ( 0 ) using parallel plate capacitors. Measure the permeability constant (μ 0 ) using solenoids. Measure the speed of light (c). Theoretical Backgrounds 1. Propagation of electromagnetic wave The speed of light (any electromagnetic wave) in vacuum has the exact value: c = 299 792 458 m/s. (a) Usually, a wave requires a medium (some material) through which or along which to travel. (b) An electromagnetic wave, including light wave, does not require any medium. It can propagate in an empty space. (c) Speed of light in vacuum is c = 1 √ μ 0 0 where μ 0 and 0 are permeability and permittivity in vacuum respectively. (d) Light has the same speed regardless of the frame of reference in which it is measured. (e) Light travels through a medium such as air or glass. In that case the electromagnetic properties of the medium slow down the speed of light as c → v = c n , where n is the index of refraction of that medium. 2. Permeability μ determines the strength of the magnetic field due to a source current. For example, the Ampere’s law that describes the magnetic field in a medium reads I C B · ds = μi enc , where C is a closed loop and i enc is the current passing through the area surrounded by the loop C . In the vacuum it is μ = μ 0 , where μ 0 =4π × 1.000 000 000 82(20) × 10 -7 H/m. The relative permeability μ r is defined in such a way that μ = μ r μ 0 . The μ r depends on the magnetic properties of the medium. 3. Permittivity ε determines the strength of the electric field due to a source charge. For example, the Coulomb’s law that describes the electrostatic force F 2→1 on particle 1 with charge q 1 by particle 2 with charge q 2 in a medium reads F 2→1 = 1 4πε q 1 q 2 r 2 ˆ 2→1 , where r is the distance between the two charged particles and ˆ 2→1 is the unit vector directed from 2 to 1. In the vacuum the permittivity is ε = ε 0 , where ε 0 ≡ 1 c 2 μ 0 =8.854 187 8128(13) × 10 -12 F/m. Except for vacuum ε>ε 0 . ε = ε r ε 0 , where ε r is the relative permittivity and depends on the electric properties of the medium made of a dielectric material. The relative permittivity ε r is also called the dielectric constant. 4. Parallel Plate Capacitor Consider a parallel plate capacitor of cross sectional area A, distance d. (a) If the space between the two plates is empty, then the capacitance is C = ε 0 A d . 2020 KPOPE All rights reserved. Korea University Page 1 of 5