NO: EXPRIMENT 06 GENRAL PHYSICS COURSE NO. BSCS-307
RESISTANCE:
The electrical resistance of an electrical element measures its opposition to the passage of an electric current; the inverse quantity is electrical conductance, measuring how easily electricity flows along a certain path. Electrical resistance shares some conceptual parallels with the mechanical notion of friction. The SI unit of electrical resistance is the ohm (), while electrical conductance is measured in Siemens (S). An object of uniform cross section has a resistance proportional to its resistivity and length and inversely proportional to its cross-sectional area. All materials show some resistance, except for superconductors, which have a resistance of zero.
OHMS LAW:
The resistance of an object is defined as the ratio of voltage across it to current through it:
R=V/I
For a wide variety of materials and conditions, the electrical resistance R is constant for a given temperature; it does not depend on the amount of current through or the potential difference (voltage) across the object. Such materials are called Omega materials. For objects made of omega materials the definition of the resistance, with R being a constant for that resistor, is known as Ohm's law
DEFINITION OF 1 OHM:
The ohm is defined as a resistance between two points of a conductor when a constant potential difference of 1 volt applied to these points, produces in the conductor a current of 1 ampere the conductor not being the seat of any electromotive force OMEGA=V/A=M^2.Kg/s.C^2=J/s.A^2=kg.m^2?s^3.A^2=J.s/C^2 In many cases the resistance of a conductor in ohms is approximately constant within a certain range of voltages, temperatures, and other parameters; one speaks of linear resistors. In other cases resistance varies (e.g., thermostats). Commonly used multiples and submultiples in electrical and electronic usage are the milliohm, ohm, kilo ohm, and mega ohm. In alternating current circuits, electrical impedance is also measured in ohms.
FOLLOWING DIFFERENT WAYS TO FIND THE UNKNOWN RESISTANCE:
1. 2. 3. 4. 5.
Unknown resistance by using a neon flash lamp and a capacitor. Measurement of unknown resistance using Carey-Fosters Bridge To determine the value of unknown resistance using voltmeter To determine the value of unknown resistance using potentiometer
WHAT IS CONDENSER?
ANS: In a laboratory a condenser is a piece of laboratory glassware used to cool hot vapors or liquids. A condenser usually consists of a large glass tube containing a smaller glass tube running its entire length, within which the hot fluids pass.
OR Surface condenser is the commonly used term for a water-cooled shell and tube heat exchanger installed on the exhaust steam from a steam turbine in thermal power stations.
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THEORY OF THIS EXPERIMENT:
In this practical capacitance, the time of flash is directly proportional to the resistance. i.e. tr
or t=K r A number of resistances are taken and time for say 10 flashes is noted for each of them. Plot the graph b/w t and r. Time of flashes for unknown resistance x is noted the value of x can be read the from graph. You may extend the experiment to determine the capacity of unknown condenser
WHAT IS NEON FLASHBULB?
ANS: A neon lamp (also neon glow lamp) is a miniature gas discharge lamp that
typically contains neon gas at a low pressure in a glass capsule. Only a thin region adjacent to the electrodes glows in these lamps, which distinguishes them from the much longer and brighter neon tubes used for signage. The term "neon lamp" is generally extended to lamps with similar design that operate with different gases. Neon glow lamps were very common in the displays of electronic instruments through the 1970s; the basic design of neon lamps is now incorporated in contemporary plasma displays.
STOP WATCH:
A stopwatch is a handheld timepiece designed to measure the amount of time elapsed from a particular time when activated to when the piece is deactivated. A large digital version of a stopwatch designed for viewing at a distance, as in a sports stadium, is called a stop clock.
POWER SUPPLY:
A power supply is a device that supplies electrical energy to one or more electric loads.
The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy (e.g., mechanical, chemical, solar) to electrical energy.
A regulated power supply is one that controls the output voltage or current to a specific value; the controlled value is held nearly constant despite variations in either load current or the voltage supplied by the power supply's energy source. Every power supply must obtain the energy it supplies to its load, as well as any energy it consumes while performing that task, from an energy source. Depending on its design, a power supply may obtain energy from:
A.C POWER SUPPLY:
An AC power supply typically takes the voltage from a wall outlet (mains supply, often 230v in Europe) and lowers it to the desired voltage (eg 9vac). As well as lowering the voltage some filtering may take place. An example use for an AC power supply is powering certain guitar effects pedals (e.g. the Digitech Whammy pedal) although it is more common for effects pedals to require DC.
D.C POWER SUPPLY:
An AC powered unregulated power supply usually uses a transformer to convert the voltage from the wall outlet (mains) to a different, nowadays usually lower, voltage. If it is used to produce DC, a rectifier is used to convert alternating voltage to a pulsating direct voltage, followed by a filter, comprising one or more capacitors, resistors, and sometimes inductors, to filter out (smooth) most of the pulsation. A small remaining unwanted alternating voltage component at mains or twice mains power frequency (depending upon whether half- or full-wave rectification is used)rippleis unavoidably superimposed on the direct output voltage.
For purposes such as charging batteries the ripple is not a problem, and the simplest unregulated mains-powered DC power supply circuit consists of a transformer driving a single diode in series with a resistor.
AC/DC supply:
In the past, mains electricity was supplied as DC in some regions, AC in others. Transformers cannot be used for DC, but a simple, cheap unregulated power supply could run directly from either AC or DC mains without using a transformer. The power supply consisted of a rectifier and a filter capacitor. When operating from DC, the rectifier was essentially a conductor, having no effect; it was included to allow operation from AC or DC without modification.