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Statement (I): The epicyclic gear train has a central gear and an epicyclic gear which produces epicyclic motion being moved by a crank arm. Statement (II): The arm contains the bearings for the epicyclic gear to maintain two gears in mesh. 

Statement (I): The epicyclic gear train has a central gear and an epicyclic gear which produces epicyclic motion being moved by a crank arm. Statement (II): The arm contains the bearings for the epicyclic gear to maintain two gears in mesh.  Correct Answer Both Statement I) and Statement II) are individually true but Statement II) is not the correct explanation of Statement I)

An epicyclic gear train also known as planetary gear consists of two gears mounted so that the center of one gear revolves around the center of the other.  Epicyclic gear sets essentially consists of two gears with their axes or shafts connected to an arm or carrier. If the arm is fixed, the gear train is simple and gear A can drive gear B or vice versa, but if gear A is fixed and the arm is rotated about the axis of gear A , then the gear B is forced to rotate upon and around  gear.

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The epicyclic gear trains may be simple or compound. Compound epicyclic gear trains are called planetary gear train.

So, from above explanation Statement I) is correct as it gives the definition of epicyclic gear set.

Moreover, arm   has bearing at ends which connect the end of arm with centre of gears maintaining two gears in mesh. Statement II) is also correct but does not explain statement I).

Applications: The epicyclic gear trains are useful for transmitting high velocity ratios with gears of moderate size in a comparatively lesser space. These are used in the back gear of lathe, differential gears of the automobiles, hoists, pulley blocks, wrist watches etc.

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