An Incandescent Lamp Experiment

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In an incandescent lamp experiment, the resistance of the filament wire will increase noticeably as it temperance from room temperature to handling temperature. If the supply voltage was increased in a lamp circuit, the consequent increase in current would give rise to the filament to increase temperature, which would take turns increase its resistance, therefore preventing further increases in current there is not further increase in supply voltage. Hence, voltage and current do not follow the ohm's law equation: V=IR, because an incandescent lamp's filament resistance does not maintain stable for various currents. The appearance of resistance varying with alteration in temperature is one shared by nearly all metals, and which at most wires are made.In an ideal case, the straight line plot of current over voltage state clearly that resistance is stabilized, unchanging value for a comprehensive of circuit currents and voltages.

Resistors, which are made to offer an exactly, stable value of resistance. This phenomenon and behavior can call as 'linear'.

Photovoltaic Cell

A photovoltaic cell is a specialized semiconductor diode that transforms visible light into direct current (DC). Certain photovoltaic cells can also transform infrared or ultraviolet radiation into DC electricity. Photovoltaic cells are an unabridged section of solar electric energy systems.There are two fundamental types of semiconductor material, which are P type (Positive) and N type (Negative). In a photovoltaic cell, straightness pieces of these materials are lay up together, and the physical borderline between them is called the P-N junction. The equipment is fabricated in such a way that the junction can be disclosed to visible light, infrared, or ultraviolet radiation.

When such radiations penetrate the P-N junction, a voltage divergence is produced between the P type and N type materials. Electrodes joint to the semiconductor layers enable current to be drawn from the equipment.The materials applied in photovoltaic cell have various spectral responses to incident light, and display a different sensitivity with respect to the in-take of photons at offered wavelengths. Each of the semiconductor material will have an incident radiation threshold frequency, below that, there is no electrons will be dependence to the photovoltaic effect. An increasing number of light intensity will appropriately increase the proportion of photoelectron emission in the photovoltaic material.

In veritable applications, the light absorbent by a solar cell will be an integration of direct solar radiation, as well as proliferate light bounced off of surrounding appearances.


Phototransistor are planned specifically to take superiority of this fact. The most general variants are an NPN bipolar transistor with an exposed base region. The phototransistor is like a diodes, all transistors are light sensitive. Light striking the base substitutes what would popularly be voltage applied to the base. A phototransistor amplifies changes in the light striking it.

The phototransistor may not have a base lead.The phototransistor is analogical in manipulation to the amplifying transistor, but it is bounded by light instead of the electric current of the emitter. It also applies a piece of germanium but only a unitary collector wire. The top end of this wire rests in a limited dimple ground into one side of the germanium disk. At this stage the germanium disk is only three thousandths of an inch thick.The light focused on the opposite, an un-dimpled side of the disk can dominate the flow of current in the wire, therefore making a dominate device analogical in function to a photo-electric cell.Furthermore, the phototransistor has a high power output for a photo-electric equipment and supplies great response to a quickly fluctuating light source.

It is especially sensitive to the wavelengths of light supplied off by common incandescent light bulbs, and is very good to manipulate with these easily available sources with great accurate. Another advantage is the device's low impedance.

Photoconductive cell, LDR

The photoconductive cell is also referred to as photo resistor. It has the character that its specific resistance varies as a operation of the incident illumination, called as photoconductivity effect. The Photo resistor can know as LDR (light dependent resistor).The photoconductive cell is applied for detecting and surveying electromagnetic radiations. It is referenced on the basis of the theory of transformation of conductivity.

Its conductivity varies in accordance with the intensity and wavelength of the incident radiation.LDR (light dependent resistor), a two terminal semiconductor equipment, two terminals are linked to a thin coating of the photoconductive material. This coating includes some impurities. The conductivity of the materials is relative to the consistence of charge carriers present. The light energy gave to the semiconductor causes covalent bonds to be damaged and produce hole-electron pairs. These strengthen current carriers' decreases the resistance of the material.

Therefore, a device is called photo resistor or Opto- conductor.Be short of light, the resistance of the material will be increase. Only a limited number of current may flows through the photo resistor. These amounts of current are called as dark current and the resistance relevant to this current is called dark resistance.

These kind of resistance will likely as high as few mega ohms. After exposed, the resistance of the photo resistor reduces and a great current called joint current flows across it. The variant between joint current and the dark current is called photocurrent.Photocurrent = joint current - dark current

PIN Photodiode

The structure of the PIN photodiode light sensor is analogical to that of a common PN-junction diode apart from the diodes outer cover is transparent so that light can fall approach the junction. The LED can be applied as photodiodes as it can deliver and detect light source. All PN-junctions are light sensitive and applied in a photoconductive pattern with the PN-junction of the photodiode invariably reverse biased. Only the diode spillage or dark current can flow in.

This reverse bias situation causes an increase of the expend boundary which is the sensitive portion of the junction.When the light source fall upon the junction, more electrons and holes are shaped and the spillage current will increases. The spillage current increases as the lighting or illumination of the junction aggrandize. The current of diode is immediately relative to light intensity. One of the primary characteristic of photodiodes while applied as light sensors is its quick response to varies in the light levels. In the same time, the disadvantage of this form of photo device is the oppositely small current flow even when fully lit.The absorbing volume of a PN-junction is narrow and may not absorb all the incident radiation.

PIN photodiodes have a layer of intrinsic semiconductor between the P and N doped layers. This makes the absorbing volume much larger and the diode more sensitive to longer wavelengths.


The Incandescent Lamp

Figure 1.1The circuit has been connected as Figure 1.1Digital multimeter is connected as an ammeter in between the power amplifier and the lamp filament socket.The power supply has been switched ON.The 10 kΩ wirewound resistor is has been set to minimum for zero output voltage from the power amplifier.The readings of lamp filament current as indicated on the digital meter as the lamp voltage is increased in 1V steps have been taken.The results have been recorded.The corresponding values of lamp filament power and resistance have been calculated. The results have been recorded.The graphs of lamp power and resistance against applied voltage have been plotted.

Photovoltaic Cell

Figure 1.2.The circuit has been connected as Figure 1.2.The short circuit current between the Photovoltaic Cell output and ground has been measured by the used of digital multimeter.An opaque box has been fitted over the Clear Plastic Enclosure to exclude all ambient light.The power supply has been switched ON.The 10kΩ wirewound resistor has been set to minimum for zero output voltage from the power amplifier.The results have been recorded.The power supply has been switched OFF.The multimeter has been set as a voltmeter to read the Open Circuit Output Voltage.The power supply has been switched ON and results have been recorded.The graphs of Photovoltaic Cell Short Circuit Output Current and Open Circuit Output Voltage against Lamp Filament Voltage have been plotted.

The Phototransistor

Figure 1.3The circuit has been connected as Figure 1.3.The 10kΩ carbon slider contol has been set to minimum setting (1).The Phototransistor load resistance is approximately 1kΩ.The digital multimeter has been connect to measured the Phototransistor output voltage.An opaque box has been fitted over the Clear Plastic Enclosure to exclude all ambient light.The power supply has been switched ON. The 10kΩ wirewound resistor has been set to minimum for zero output voltage from power amplifier.The results have been recorded.The graph of Phototransistor Output Voltage against Lamp Filament Voltage has been plotted.

The Photoconductive Cell, LDR

Figure 1.4The digital multimeter has been connected to measure the Photoconductive Cell output voltage. An opaque box has been fitted over the Clear Plastic Enclosure to exclude all ambient light.The power supply has been switched ON. The 10kΩ wirewound resistor has been set to minimum for zero output voltage from power amplifier.The results have been recorded.The graph of Photoconductive Cell Output Voltage against Lamp Filament Voltage has been plotted.

The PIN Photodiode

Figure 1.5The circuit has been connected as Figure 1.5.The current output of the PIN Photodiode has been measured by the used of Current Amplifier.The output voltage of Amplifier #1 has been measured by the used of digital multimeter.An opaque box has been fitted over the Clear Plastic Enclosure to exclude all ambient light.The power supply has been switched ON. The 10kΩ wirewound resistor has been set to minimum for zero output voltage from power amplifier.The Gain Coarse of Amplifier #1 has been set to 10 and the Gain Fine has been set to 1.0.The Offset is giving zero output for zero input has been checked.The results have been recorded.The Current Amplifier to the Buffer Amplifier has been checked to measure the output voltage of the PIN Photodiode.The results have been recorded.The graphs of PIN Photodiode Current Amplifier Output Voltage and Buffered Output Voltage against Lamp Filament Voltage have been plotted.


Lamp filament voltage (Volts)












Lamp filament current (mA)












Lamp filament power (mW)












Lamp resistance (Ω)











0.157The Incandescent Lamp

Photovoltaic Cell

Lamp filamentvoltage(V)012345678910Short Circuit Output Current (µA) Circuit Output Voltage (V)0.0330.0510.2550.3460.3940.4260.4470.4640.4760.4880.496

The Phototransistor

Lamp filament voltage (V)012345678910Phototransistor Output Voltage554.954.563.752.0940.8110.7740.7550.7440.733

The Photoconductive Cell, LDR

Lamp filament voltage (V)012345678910Photoconductive Cell Output (V)5554.974.864.634.233.783.232.792.35

The PIN Photodiode

Lamp filament voltage (V)012345678910PIN Photodiode Current Amp. O/P000.0040.0280.0730.1890.3730.6310.9641.4031.954PIN Photodiode Output Voltage00.0010.0320.2550.8171.7202.6773.0423.2433.3903.50


Incandescent Lamp

The resistance of most conductive materials is stable over an extensive range of requirements, but this is not true of all materials.Any function that can be plotted on a graph as a straight line is called a linear function. For circuits with stable resistance, the plot of current against voltage is linear. V=IR. Similarly, in circuits where resistance different with variation in either current or voltage, the plot of current against voltage will be nonlinear, which is not a straight line.The negative resistance values are where the current through a sub-unit actually reduces as the used voltage across it is increased.

Some semiconductor diodes show negative resistance over a certain limit of voltages.

Photovoltaic Cell

6.2.1 Short Circuit Current, ISC

ISC accordance to the short circuit condition when the impedance is low and is measured when the voltage is equal to 0.ISC = I (when V=0)ISC reproduces at the initiate of the forward-bias sweep and is the maximum current IMAX value in the power quadrant. For an ideal cell, this maximum current IMAX value is the sum of the current made in the solar cell by photon excitation.ISC = IMAX = If for forward-bias power quadrant

6.2.2 Open Circuit Voltage, VOC

The open circuit voltage, VOC appears when there is no current flowing through the cell.VOC = V (when I=0)VOC is also the maximum voltage difference pass through the cell for a forward-bias sweep in the power quadrant.VOC = VMAX for forward-bias power quadrant


The phototransistor has a high level of gain consequent from the transistor action.One of the essential adverse conditions of the phototransistor is the fact that it does not have a uniquely good high frequency response. This appears from the large capacitance correlative with the base-collector junction. This junction is planned to be relatively large to enable it to acquire sufficient amount of light source. For a typical homo-structure device, the bandwidth may be restricted to about 250 kHz.The characteristic of the phototransistor under various levels of light intensities.

It is analogical to the characteristic of a traditional bipolar transistor, but with the various levels of base current interchanged by the different standard of light intensity.There is a limited quantity of current that flows in the phototransistor so much so that when there is no light source presents. This kind of situation is called the dark current, and stands for limited amount of carriers that are infused into the emitter. Similarly, the photo generated carrier is be enslaved to amplification by the transistor action.

Photoconductive Cell, LDR

When the cell is not illuminated, its resistance value may be exist 100kΩ. This resistance is defined as dark resistance.When the cell is illuminated, the resistance may fall to few hundred ohms. The scales on the illumination characteristic are logarithmic to involve a comprehensive range of resistance and illumination that are possible. The cell sensitivity may be specified in terms of the cell current for an offered voltage and offered level of illumination.The primary drawback of the photoconductive cells is that temperature modification cause a good deal of changing in resistance for a specific light intensity.

Thus, a cell is inadaptable for analogue application.When the cell is dark, its high obstruction reduces the current which drop to a low level to stimulate the relay. Resistance is consisted to limit the relay current to the required stage when the resistance of the cell is become low. Photoconductive cells are applied to switch transistors on and off.When the cell is dark, the transistor base is biased exceed its emitter stage, and the device is turned on.

Similarly, when the cell is illuminated, the lower resistance of the cell in series with resistance biases the transistor base voltage beneath its emitter stage. Therefore, the device is turned off.

PIN Photodiode

The current-voltage characteristic of a photodiode with no incident light is analogical to a rectifying diode. When the photodiode is forward biased, there is an exponential rise in the current. When a reverse bias is implemented, a limited amount of saturation current appears. It is relevant to dark current.ID = ISAT ( - 1 )When ID is the photodiode dark currentISAT is the reverse saturation currentq is the electron chargeVA is the applied bias voltageKB = 1.38 x 10-23 J/K, is the Boltzmann ConstantT is the absolute temperature (273K = 0oC)Illumination the photodiode with optical radiation, shifts the I-V curve by the amount of photocurrent (IP)ITOTAL = ISAT ( - 1 ) - IPIP is defined as the photocurrent.As the applied reverse bias enhances, there is a sharp enhances in the photodiode current. The applied reverse bias at this point is referred as breakdown voltage.

This is the maximum used reverse bias, below which, the photodiode must be manipulated.Breakdown voltage, it changes from one photodiode to another and is normally measured.

7.0 Conclusion

The DIGIAC 1750 Opto-Transducer Facilities is an integrated transducer and apparatus trainer with examples of a full range of input and output transducer, signal conditioning circuits and dispel devices. The unit is self contained and enables the characteristic of individual devices to be studied and also it's interconnection to compose a complete loop system. The only additional equipments suggested are an oscilloscope and digital multimeter.For the first experiment, Incandescent Lamp, the Ohm's law, V = IR is not very useful for analyzing the reaction of components, where the resistance changes with current and voltage. It might be more precise to call the equation as R = V/I, a definition of resistance, compatible for certain class of materials under a narrow range of conditions.Photovoltaic cell, one of the contrivance which presents for economize energy, cleaning up the environment and reducing human rely on fossil fuels.

Solar energy is the better way to save the Earth's natural resources.Phototransistor circuits are widely applied for various applications within the electronics field. Although the phototransistor symbol may vary mildly from one author to another, but the theory is the same. For the circuit configurations used, the ordinary emitter format is the most common.

Phototransistor is small size and expected long-lived, nevertheless, along with economies that perhaps reasonably result from quantity production.Photodiodes are usually applied in CD or DVD-ROM drives, cameras, scanners, remote controls, light meter and etc. When photodiode was integrated into operational amplifier circuits it can be used for infrared spectrum detectors for positioning systems, fibre optic communications, laser scanning and etc.

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