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Advanced Physics Study Course,
W. Bolton, P.131(John Murray, 1986) 有以下的一個問與答：
| Q |
If the secondary circuit
of a transformer is open the current in the primary is very small.
Why is this, .............. |
| A |
With the open circuit for the secondary,
the back e.m.f. in the primary is almost the same as the applied
potential difference, thus the net e.m.f. causing the current through
the primary resistance is very low. .....* |
Advanced Physics for Hong Kong, Tom Duncan, 3rd Ed.,
V1, P.284 有以下一段文字：
| Consider initially a mains transformer
whose primary winding has a resistance of 10 ohm; on a 240 V supply
the primary current should therefore be 240/10 = 24 A. An a.c. ammeter
connected in the primary records 0.10 A. The difference is very
large and is due to the fact that the alternating flux (arising
from the a.c. in the primary), which induces an e.m.f. in the secondary,
also induces an e.m.f. called a back e.m.f. in the primary.
This e.m.f. opposes the applied p.d. and is nearly but not quite
equal to it at every instant. The net e.m.f. in the primary
is therefore quite small. |
你同意以上的說法嗎？
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