Download Some experiments with a piece of wire

Some experiments with a piece of wire
Ryszard Poprawski
Institute of Physics
&
Wojciech Poprawski
Institute of Production Engineering and Automation
Wroclaw University of Technology
WROCLAW UNIVERSITY OF TECHNOLOGY
Some experiments with a piece of wire
Introduction
Using the simple demonstration set, which consists a piece
of wire spreaded between the two isolated from each
other handles, the source of the electric current, magnet
and oscilloscope we will presend few interesting physical
laws and phenomenas and we will show the examples of
their applications in every day life and contemporary
technology.
WROCLAW UNIVERSITY OF TECHNOLOGY
Some experiments with a piece of wire
The main part of experimental set-up is a piece of wire
spreaded between the two isolated handles. The wire is
mounted in such way, that it is easy to adjust the tension
of the wire. On the middle of the bar with handles, the
mirror with a milimetre scale is mounted. This is used for
wire deflection measurement
WROCLAW UNIVERSITY OF TECHNOLOGY
Some experiments with a piece of wire
Elastic properties (Hooke's Law)
WROCLAW UNIVERSITY OF TECHNOLOGY
Some experiments with a piece of wire
Thermal Expansion
Using the above set-up it is very easy to show thermal
expansion. The electric current is heating the wire,
which starts hanging loose down.
The thermal expansion phenomena is used for building
temperature sensors, thermostats (eg an iron, electric
kettle), circuit breakers (like indicators in cars),
thermal fuses and fluid thermostats used for example
in the refridgerators.
WROCLAW UNIVERSITY OF TECHNOLOGY
Some experiments with a piece of wire
Thermal Expansion
WROCLAW UNIVERSITY OF TECHNOLOGY
Some experiments with a piece of wire
Hot-wire anemometer
Blowing the air on the lighting wire one can notice that
the wire is changing its colour (getting darker) due to the
air which is cooling it down. In that way we have showed
that heat exchange between the wire and surrounding
medium depends on the speed of flowing. It also depends
on the angle between the wire and the air stream. It is an
example of measurement of non-electrical quantity using
electrical methods (measurement of resistance or power
etc.)
WROCLAW UNIVERSITY OF TECHNOLOGY
Some experiments with a piece of wire
Stefan-Boltzmann's Law
Energy emited by the black body is proportional to the 4th
power of its absolute temperature.
The Planck's law says that majority of the energy is
emmited as infrared radiation. Tu use Stefan-Boltzmann
law we use pyroelectric detector of infrared radiation.
So it is physical background of thermovision.
Stefan-Boltzmann law played a fundamental role in the
physics development (quatum mechanics).
WROCLAW UNIVERSITY OF TECHNOLOGY
Some experiments with a piece of wire
Ampere's Law
The electric current in the wire is creating a
rotational magnetic field. The direction of the field
can be determined using right hand or righthanded screw rules. The compass can show the
presence and the direction of the field.
WROCLAW UNIVERSITY OF TECHNOLOGY
Some experiments with a piece of wire
Faraday's Law
To show Faraday's and Ampere's Laws we can use a
coil connected to the oscilloscope.
The electromagnetic induction phenomena are used in
power plants (generators), speedometers (eg. bicycle,
car), reading data from magnetic tapes (audio, VCR,
computer discs etc) and many other things
WROCLAW UNIVERSITY OF TECHNOLOGY
Some experiments with a piece of wire
A wire with electric current in magnetic field
WROCLAW UNIVERSITY OF TECHNOLOGY
Some experiments with a piece of wire
String vibrations – standing waves
If the electric current is alternating in periodic way, the wire is
under the influence of the periodic force. When changing the
string tension, one can tune the string to resonance with the
exciting periodic force (in this case 50Hz)
WROCLAW UNIVERSITY OF TECHNOLOGY
Some experiments with a piece of wire
A wire in Earth's magnetic field
WROCLAW UNIVERSITY OF TECHNOLOGY
Some experiments with a piece of wire
Thermoelectric effects
Consists on the current (voltage) generation in the joint
of the two different metals, when the contacts are in
different temperatures.
A
T2
Hot
Cold
T1
WROCLAW UNIVERSITY OF TECHNOLOGY