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Force and Pressure — Science STD 8 — Question

Gujarat BoardEnglish MediumSTD 8ScienceForce and Pressure1 Mark
MCQ
When we press the rubber sucker on a flat, smooth surface. A rubber sucker stays attached firmly to a flat surface due to:
  • A
    Gravity of the earth inside.
  • ✓
    Low atmospheric pressure inside.
  • C
    High atmospheric pressure inside.
  • D
    High electrostatic force creates inside.
✓

Answer

Correct option: B.
Low atmospheric pressure inside.
When we press the rubber sucker on a flat, smooth surface, its concave rubber cup gets flattened to a large extent, pushing out most of the air from beneath it. Since, very little air remains inside the flattened rubber sucker, therefore, the air pressure inside the rubber sucker becomes very low $($and a partial vacuum is created$)$. The much greater atmospheric pressure acting on the rubber sucker from outside fixes the rubber sucker firmly on the flat surface.

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