An electric device delivers a current of [tex]$15.0 A$[/tex] for 30 seconds. How many electrons flow through it?
Answer (2)
The question deals with the topic of why a petrol fire cannot be extinguished by pouring water on it and provides an assertion and a reason to evaluate.
Analysis:
Assertion (A): Petrol fire can't be extinguished by pouring water over it.
True: Petrol is a hydrocarbon and it is lighter than water, which means it will float on water. When water is poured over a petrol fire, the petrol remains on top and continues to burn. Additionally, water can spread the petrol further, potentially expanding the fire.
Reason (R): Water is heavier than petrol.
True: As mentioned, the density of petrol is less than that of water, which is why petrol will float on the surface rather than mix with water.
Conclusion:
Both the assertion and the reason are true statements. However, the reason provided (R) is not the correct explanation for why petrol fire cannot be extinguished by pouring water over it. The main reason is that pouring water on petrol will not smother or exclude the oxygen needed for the fire to burn, and instead, it may spread the petrol, making things worse.
Correct Choice:
B. Both A and R are true but R is not the correct explanation of A.
This is because while it's true that water is heavier than petrol, this fact doesn't directly explain why water shouldn't be used to put out a petrol fire. The correct explanation involves the behavior of petrol floating and possibly spreading when water is applied.
The device delivers a current of 15.0 A for 30 seconds, resulting in a total charge of 450 C . Using the charge of a single electron, we calculate that approximately 2.81 × 1 0 21 electrons flow through the device during this time.
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