question_answer

Assertion  :         When a beetle moves along the sand with in a few tens of centimeters of a sand scorpion the scorpion immediately turn towards the beetle and dashes to it Reason                 :   When a beetle disturbs the sand, it sends pulses along the sands surface one set of pulses is longitudinal while other set is transverse.          [AIIMS 2003]

A)             If both assertion and reason are true and the reason is the correct explanation of the assertion.

B)             If both assertion and reason are true but reason is not the correct explanation of the assertion.

C)             If assertion is true but reason is false.

D)             If the assertion and reason both are false.

E)             If assertion is false but reason is true.

Correct Answer: A

Solution :

                   A beetle motion sends fast longitudinal pulses and slower transverse waves along the sends surface. The sand scorpion first intercept the longitudinal pulses and learns the direction of the beetle; it is in the direction of which ever leg is disturbed earliest by the pulses. The scorpion then senses the time interval (Dt) between that first interception and the interception of slower transverse waves and uses it to determine the distance of the beetle. The distance is given by \[\Delta t=\frac{d}{{{v}_{t}}}-\frac{d}{{{v}_{l}}}\]