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In a D.C. generator the critical resistance can be increased by
Answer & Solution
Correct Answer:
Option
C
Explanation:
The critical resistance is the maximum field resistance for a DC generator to begin voltage buildup or excitation.
It is the resistance represented by the tangent to the O.C.C (Open Circuit Characteristic) curve of a DC generator.
The O.C.C curve shows the relationship between the generated EMF and field current at a constant speed.
If we increase the speed of the generator, the generated EMF increases at a given field current.
This means the O.C.C curve shifts upwards.
A steeper O.C.C curve (at higher speed) allows for a higher tangent, hence a higher critical resistance.
Changing the field resistance doesn't directly affect the critical resistance. It affects the operating point after the generator has built up voltage, but not the initial build-up.
Therefore, the correct answer is increasing its speed. Option C is the correct answer.
The critical resistance is the maximum field resistance for a DC generator to begin voltage buildup or excitation.
It is the resistance represented by the tangent to the O.C.C (Open Circuit Characteristic) curve of a DC generator.
The O.C.C curve shows the relationship between the generated EMF and field current at a constant speed.
If we increase the speed of the generator, the generated EMF increases at a given field current.
This means the O.C.C curve shifts upwards.
A steeper O.C.C curve (at higher speed) allows for a higher tangent, hence a higher critical resistance.
Changing the field resistance doesn't directly affect the critical resistance. It affects the operating point after the generator has built up voltage, but not the initial build-up.
Therefore, the correct answer is increasing its speed. Option C is the correct answer.
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LoginCritical resistance (Rc) is the maximum field circuit resistance above which the generator will fail to build up voltage.
The open-circuit characteristic (OCC) shifts upward when the speed increases because generated emf ∝ speed.
When OCC rises upward, the slope increases, which means the generator can tolerate higher field resistance, so critical resistance increases.
Therefore:
✔ Increasing speed → OCC becomes steeper → critical resistance increases.
Rc=(Emf/Field Current)
so we must inceasing the speed to tangent the the new speed curve