關於物理的簡單問題 - Ans.fyi 參考答案

關於物理的簡單問題

Tieria

2010-04-04 3:18 am

1. Two light bulbs with ratings ‘2 V, 3 W’ and ‘2 V, 4 W’ are connected in parallel to a 2 V rechargeable cell. Initially, 106 J of electrical energy is stored in the cell. Estimate how long the cell can light up the bulbs continuously.
A. 39.7 h
B. 79.4 h
C. 162 h
D. 1940 h

2. An unqualified electrician wrongly connects the wires inside a 3-pin plug of a common electric iron so that the live wire is connected to the neutral pin while the neutral wire is connected to the live pin. Which of the following situations will happen?
A. The iron will burn out when it is switched on.
B. He will get an electric shock immediately when he switches on the iron.
C. The heating element of the iron will not heat up when it is switched on.
D. The heating element of the iron still stands at high potential even its switch is OFF.

回答 (1)

天同

2010-04-04 3:39 am

✔ 最佳答案

1. Total power consumed by the 2 bulbs = (3 + 4) w = 7 w = 7 J/s
Hence time the cell can last = 10^6/7 s = 142857 s = 39.7 hrs.

2. This is apparent. The neutral wire connected to the heating element directly. If it is connected to the "Live" socket, there is a potential at the heating element.

Option C is wrong because when the switch is closed, there is still a complete circuit. Current still passes through the heating element to make it works.

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