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 WROCLAW UNIVERSITY OF TECHNOLOGY Elastic properties (Hooke's Law)

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 4 th 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 right- handed 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. WROCLAW UNIVERSITY OF TECHNOLOGY Cold AA Hot T 2 T 1