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Which of the following factors will NOT affect the selection of a resistor?
Frequency range
Tolerance
Thermal resistivity
Power rating (in watts)
Frequency range
Resistor selection is primarily governed by electrical ratings and physical properties, such as tolerance, power rating, and thermal characteristics. Frequency range is generally not a primary design factor for standard resistive applications unless the component operates at high radio frequencies where parasitic capacitance and inductance become significant.
IS 578:1985 (Specifications for Fixed Resistors)
Resistor selection is primarily governed by electrical ratings and physical properties, such as tolerance, power rating, and thermal characteristics. Frequency range is generally not a primary design factor for standard resistive applications unless the component operates at high radio frequencies where parasitic capacitance and inductance become significant.
P=I2R тАФ Power rating formula based on current and resistance
RTтАЛ=R20тАЛ[1+╬▒(TтИТ20)] тАФ Temperature coefficient formula for resistance change
fcтАЛ=2╧АRC1тАЛ тАФ Cut-off frequency relation where parasitic capacitance affects performance
Resistors are passive components governed by Ohm's Law V=IR. Selection parameters like power rating (P=I2R) ensure heat dissipation safety, tolerance determines precision (RactualтАЛ=RnominalтАЛ┬▒Tolerance), and thermal resistivity dictates how effectively a material prevents or manages heat flow. At high frequencies, however, ideal resistors exhibit non-ideal reactive behavior due to internal geometry.
Tolerance defines the allowed percentage variation from the nominal resistance value.
Power rating is the maximum wattage the resistor can dissipate continuously without damage.
Thermal resistivity (or thermal coefficient) relates to resistance stability under temperature variations.
At high frequencies (MHz/GHz range), parasitic elements necessitate non-inductive or thin-film resistors, making frequency relevant only in specialized designs.
Ensures safe circuit operation within thermal limits
Maintains required circuit precision through tolerance selection
Overspecifying power rating increases physical size and cost
Tight tolerance resistors are significantly more expensive to manufacture
Voltage division in electronic circuits
Current limiting in LED and transistor biasing
The official answer key considers 'Frequency range' as the parameter that does NOT affect general-purpose resistor selection compared to the listed critical parameters.
Option B (Tolerance) is critical for accuracy in sensitive feedback circuits.
Option C (Thermal resistivity) is vital for high-power applications to prevent thermal runaway.
Option D (Power rating) is fundamental for basic thermal safety.
A is correct тАФ Frequency range is not a primary design parameter for selecting standard general-purpose resistors, unlike power rating, tolerance, and thermal properties.
In high-frequency AC circuit analysis, always check if the resistor is 'non-inductive' to avoid parasitic effects, even if it is not a primary selection criterion for general DC circuits.
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