An Englishman was showing a foreign visitor around London. “What’s that strange building?” asked the visitor. “That's the Tower of London.” “I see. How long did it take to build it?” “About 500 years.” “In my country we can build it in five months,” Shortly after that they came to St. Paul's Cathedral(大教堂). “Very interesting!” said the visitor. “How long did it take to build it ?” “Near forty years.” said the Englishman. “In my country we can finish it in forty days at most,” said the visitor. This went on all day.
They visited most of the best known buildings in the city. Every time they saw a new one, the visitor asked what it was and how long it took to build it. Then he said that they could do the same thing much faster in his country.
At last the Englishman got angry with the visitor though he tried not to show it. Several days later they came to the House of Parliament(议会)and the visitor asked his usual question, “What is that?” The Englishman answered, “ I have no idea. It wasn't there last night.”
T时，原线圈的电流i＝30 mA，由此可知，此变压器的原副线圈匝数之比为( )