In a gear having involute teeth, the normal to the involute is a tangent to the

Solution (By Examveda Team)

An involute gear tooth profile is the most commonly used tooth shape in gear design. It is generated by tracing the end of a taut string unwinding from a circle. The resulting curve is known as the involute of a circle.

The base circle is the circle from which the involute profile is generated. It plays a crucial role in defining the geometry of involute gear teeth.

Correct Answer: Option B – Base circle

Explanation:
In gears with involute teeth, the normal to the involute profile at any point is always tangent to the base circle from which the involute is generated. This is a fundamental property of the involute curve.

As the involute curve is traced by unwinding a string from the base circle, the direction of the tension (which is always tangential to the base circle) becomes the normal to the involute curve at the point of contact. This ensures constant velocity ratio and smooth power transmission in gear systems.

Therefore, the line normal to the tooth profile at the point of contact always touches the base circle tangentially, confirming that the base circle is essential in defining the involute geometry.

Why other options are incorrect:
Option A: Pitch circle – The pitch circle is an imaginary circle where the gear teeth theoretically engage. It is not the reference circle for generating the involute profile.
Option C: Addendum circle – This is the outermost circle of the gear, representing the tips of the teeth. It is not involved in generating the involute.
Option D: Dedendum circle – This is the root circle of the gear, below the pitch circle. It also has no role in defining the involute shape.

Conclusion:
In a gear with involute teeth, the normal to the involute curve is always tangent to the base circle. Hence, the correct answer is Option B.