1. A bulb has a rating of ‘200V, 60W’. If it is connected to a 220V power supply, which of the following will most likely happen?
A. The power dissipated will be lower than 60W.
B. The working life of the bulb will be much longer.
C. The working resistance of the bulb will be smaller.
D. More electrical energy from the source will be converted into light energy in every second.
The answer is D.
2. An electron is projected towards a region where a downward magnetic field is applied. Which of the following correctly describes the path of the electron?
A. It bends upwards.
B. It bends downwards.
C. It bends out of paper.
D. It bends into the paper.
The answer is C.
※ 試列明計算步驟及各點對與錯之原因！※
ELECTRICITY & ELECTROMAGNETISM
2010-03-21 6:30 am
回答 (2)
2010-03-21 7:02 am
✔ 最佳答案
1. Option A is wrong. Power is proportional to the square of applied voltage. A higher voltage (220v vis 200v) will increase the power.Option B is wrong. Over-rated bulb will have its life shortened because it is operated at a higher temperature, and leads to more heat generated.
Option C is wrong. A higher working voltage leads to larger power, which in turn causes more heat produced. The resistance of the bulb will then be higher at higher temperature.
Option D is right. More power consumed means more light energy is produced.
2. First find the direction of the conventional current which is equivalent to the given direction of the electron.
Assume the the electron travels from left to right (is there a diagram given...?), the conventional current equivalent to this direction of motion of the electron is thus from right to left.
Applying Fleming's Left Hand Rule (Motor Rule), the direction of the magnetic force can be found to be out from the paper.
2010-03-21 7:08 am
1.由於輸入電壓比額定值高一成，而燈泡內阻值不變，所以輸出功率係正比於輸入電壓，燈泡自然比較光。
2.電子流係會受磁力場影響偏轉，但題目上向下磁力場不能說明極性如何，而你所撰答案亦頗玩味，究竟paper一字所指為何。
2.電子流係會受磁力場影響偏轉，但題目上向下磁力場不能說明極性如何，而你所撰答案亦頗玩味，究竟paper一字所指為何。
收錄日期: 2021-04-29 17:33:25
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