Some experiments with a piece of wire

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Some experiments with a piece of wire

• Ryszard Poprawski
• Institute of Physics
• Wojciech Poprawski
• Institute of Production Engineering and
  AutomationWroclaw University of Technology

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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.

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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

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Some experiments with a piece of wire
Elastic properties (Hooke's Law)
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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.

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Some experiments with a piece of wire

• Thermal Expansion

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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.)

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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).

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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
  right-handed screw rules. The compass can show
  the presence and the direction of the field.

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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

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Some experiments with a piece of wire

• A wire with electric current in magnetic field

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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)

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Some experiments with a piece of wire

• A wire in Earth's magnetic field

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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.