NAEST 2020 Blowing a Balloon inside a Syringe and Air Pressu
By Question: 1: The video shows a balloon kept inside a syringe barrel. When the piston is pulled, in that situation the pressure of the air inside the balloon is $P_1$, that outside the balloon but inside the syringe is $P_2$ and that outside the syringe is $P_3$. Choose the correct option.
- $P_1 > P_2 > P_3$
- $P_1 > P_2$, $P_2 < P_3$
- $P_1 = P_2$, $P_2 < P_3$
- $P_1 < P_2 < P_3$
- none of these
- $P_1 > P_2 > P_3$
- $P_1 > P_2$, $P_2 < P_3$
- $P_1 = P_2$, $P_2 < P_3$
- $P_1 < P_2 < P_3$
- इनमें से कोई नहीं
उस परिस्थिति पर विचार करें जब सीरिंज का नोजल अंगूठे से दबा कर बंद कर दिया गया है परंतु पिस्टन को अभी पीछे नहीं खींचा गया है। इस परिस्थिति में बैलून के अंदर का दाब $P_1$ है, बैलून के बाहर परंतु सीरिंज के अंदर की हवा का दाब $P_2$ है तथा सीरिंज के बाहर की हवा का दाब $P_3$ है । सही विकल्प चुनें।
- $P_1 > P_2$
- $P_1 = P_2$
- $P_1 < P_2$
- $P_2 > P_3$
- $P_2 = P_3$
- $P_2 < P_3$
Solution 1: Option (B) is correct.
When the nozzle of the syringe is open (i.e., it is not pressed with thumb), $P_2=P_3$ because the air outside the syringe is connected to the air inside the syringe. On closing the nozzle, the air outside side the syringe gets disconnected from the air inside the syringe. The pressures remain the same until the piston is pulled. When the piston is pulled, the volume of the air inside the syringe increases and the pressure $P_2$ decreases. Thus, $P_2 < P_3$.
What about the pressure $P_1$ inside the balloon. The balloon is made of elastic rubber. The pressure inside a blown-up balloon is always greater than the pressure outside it (otherwise the balloon will crumble). Thus, $P_1 > P_2$.
Solution 2: Options (A) and (E) is correct. The explanation is given in solution 1.
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