question_answer

In the following questions, Statement of assertion (A) is followed by a statement of reason (R).       1. If both assertion and reason are true and the reason is the correct explanation of the assertion, then mark. 2. If both assertion and reason are true but the reason is not the correct explanation of the assertion, then mark. 3. If assertion is true statement but reason is false, then mark. 4. If both assertion and reason are false statements then mark.

Assertion: When a beetle moves along the sand within a few tens of centimeters of a sand scorpion, the scoprion immediately turns towards the beetle and dashes towards it. Reason: When a beetle disturbs the sand sends pulses along the sands surface. One of plates is longitudinal while the other set is transverse.

A)  1

B)                                        2                            

C)        3                            

D)        4

Correct Answer: A

Solution :

The sand scorpion shown in the diagram uses waves of both transverse and longitudinal motion to locate its prey. When a beetle even slightly disturbs the sand, it sends pulses along the sands surface. One set of pulses is longitudinal, travelling with speed \[{{V}_{L}}\]. A second set is transverse travelling with speed \[{{V}_{T}}\]. The scorpion with its eight legs spread roughly in a circle intercepts the faster longitudinal pulses first and learns the direction of the beetle, it is in the direction of whichever leg is disturbed earliest by the pulses . The scorpion then senses the time Interval \[(\Delta t)\]between the first interception and the interception of the slower transverse waves and uses it to determine the distance d to the beetle. \[\Delta t=\frac{d}{{{V}_{T}}}-\frac{d}{{{V}_{L}}}\] which gives the scorpion a perfect fix on the beetle.