This question was previously asked in

UP Jal Nigam E&M 2016 Official Paper

Option 1 : m = D/T

__Explanation:__

Terms used in specification and design of the gear

Pitch circle: It is the imaginary circle on which two mating gears seem to be rolling. And the diameter of this circle is known as pitch circle diameter (D).

Circular pitch: It is the distance measured on the circumference of pitch circle from a point of one tooth to the corresponding point on the tooth.

\({P_c} = \frac{{\pi ~ \times ~D}}{T}\)

Module: It is the ratio of the pitch circle diameter (D) to the number of teeth (T).

\(m=\frac DT\)

Diametral pitch: It is the ratio of numbers of teeth (T) to the pitch circle diameter (D).

\({P_d} = \frac{T}{D}\)

__Additional Information__

Other terms used in gear are

- Addendum Circle: It is the circle drawn through the top of the teeth and is concentric with the pitch circle. It is also called the Outside circle.
- Dedendum circle: It is the circle drawn through the bottom of the teeth. It is also called the root circle.
- Base Circle: It is the circle from which the involute tooth profile is developed.
- Addendum: It is the radial distance of a tooth from the pitch circle to the top of the tooth (or addendum circle).
- Dedendum. It is the radial distance of a tooth from the pitch circle to the bottom of the tooth (or dedendum circle).
- Land: The top land and bottom-land are surfaces at the top of the tooth and the bottom of the tooth space respectively.
- Working depth: This is the distance of the engagement of two mating teeth and is equal to the sum of the addendum of the mating teeth of the two gears. It is the radial distance from the addendum circle to the clearance circle.
- Whole depth/Total depth: This is the height of a tooth. It is the radial distance between the addendum and the dedendum circles of a gear. It is equal to the sum of the addendum and dedendum.