On heating, the resistance of a semiconductora)increasesb)decreasesc)r...
Key Points
- On heating, bonds between the electrons of semiconductors break because of the energy gained due to heating.
- Electrons become free & help in the conduction of electric current if there is a potential difference applied across the semiconductor.
- Hence the resistance decreases on heating.
Resistance:
- It is the ability of the material to oppose the flow of current through the conductor.
- It depends on the following factors:
- Length.
- Area.
- Temperature.
- Type of material.
- R = p L / A.
- Where p = resistivity of the material.
- L = length of the conductor.
- A = cross-sectional area of the conductor.
- SI Unit = Ohm.
- In the case of a conductor, resistance increases on heating.
Resistivity:
- It is the electrical property of a material that determines the resistance of a conductor.
- It depends upon the nature & temperature of the material.
- SI unit: Ohm- metre.
Semiconductor:
- It is the type of material having conductance lesser than conductor & resistance lesser than insulators.
- They do not have free electrons at normal temperatures.
- On heating, the electrons get free & they behave like a conductor.
- The entire electronic system is based on semiconductor devices.
- Materials like Si, Ge, As etc are semiconductors.
- A pure semiconductor is neither n-type nor p-type.
- Both p-type & n-type semiconductor is electrically neutral.
- It is of two types:
- Intrinsic:
- It is a semiconductor in pure form.
- E.g: Germanium (Ge), Silicon (Si) etc.
- Extrinsic:
- It is a semiconductor mixed with a suitable impurity to increase its conductivity.
- It is further classified into two groups:
- n-type: It is mixed with pentavalent impurity like As, Sb etc. in which negatively charged electrons work as charge carriers.
- p-type: It is mixed with trivalent impurity like Al, B etc. in which positively charged holes work as charge carriers.
On heating, the resistance of a semiconductora)increasesb)decreasesc)r...
Understanding Semiconductor Resistance on Heating
When a semiconductor is heated, its resistance typically decreases due to several key factors:
Carrier Concentration
- In semiconductors, electrical conductivity is primarily due to charge carriers, namely electrons and holes.
- At elevated temperatures, thermal energy excites more electrons from the valence band to the conduction band.
- This process increases the number of free charge carriers available for conduction.
Increased Conductivity
- The increase in charge carriers enhances the material's conductivity.
- As a result, the resistance of the semiconductor decreases, allowing more current to flow.
Temperature Coefficient of Resistance
- Semiconductors have a negative temperature coefficient of resistance, meaning that as temperature increases, resistance decreases.
- This behavior is contrary to metals, where resistance generally increases with temperature.
Applications and Implications
- The property of decreasing resistance with temperature is essential in various applications, such as thermistors, which are temperature-sensitive resistors.
- Understanding this behavior is crucial for designing circuits that involve temperature variations.
In summary, the correct answer is option 'B' because, upon heating, the resistance of a semiconductor decreases due to the increased number of charge carriers resulting from thermal excitation. This unique characteristic is pivotal in many electronic devices and systems.
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