Exam text content

 

konsta hu 9 Ohdt. JI

SMG-8146 RF-electronics preparatory II

Small Exam II 05.12.2011

Answer to three of the four guestions.

Each guestion gives maximum of five points
Jari Kangas

1. Consider a pair of parallel wires in air, in which a DC current I and -I flows, respectively. See
the picture below for a cross-section of the case. Explain how to obtain field lines of the related
magnetic field and also draw enough field lines to sketch the field.

2. Correct or incorrect? To get points, support your answer by an argument or an example.

(a
(b) In insulators the Faraday's induction law does not apply, because no current can get induced
in an insulator. (1 p)

Retarded potentials are related to finite velocity of information. (1 p)

(e) It is possible even in a general time dependent case to express the electric field using scalar
potentials. (1 p.)

(d) The magnetic dipole is formed to two poles, North and South poles. (1 p)
(e) The magnetic susceptibility relates B and M. (1 p)
3. (a) Uniform plane wave that propagates in an insulator (g = 1, o = 0) has following E-field
E(r,t) = u; cos 108; £ 5
(r, 1) = ur cos( Ba
i. Find the freguency and wavelength of the wave.
ii. What is the dielectric constant of the medium?
iii. Find the corresponding H-field.

(b) Describe upon which factors do the velocity of light depend. Give examples of what kind
of values it can assume and consider also possible conseguencies if we are to use EM waves
to transmit information.

4. (a) Define polarization of a wave, give also examples of it.

(b) Describe what is so called skin depth and explain briefly its physical background.