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问题 选择题

把电热器接到110V的直流电源上，t秒内产生热量为Q，现把它接到交流电源上，t秒内产生的热量为2Q，则交流电源的电压有效值是（　　）

A．110V

B．110

2
V

C．220V

D．220

2V

答案

设电热器的电阻为R．

当电热器接在U=110V的直流电源上时，Q=

U2
R
t

当电热器改接到交流电源上时，2Q=

U′2
R
t

两式一比，得U=110

2
V

故选：B

单项选择题

厌食多见于

A．木
B．水
C．土
D．金
E．火
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单项选择题

Originally introduced by Netscape Communications, (1) are a general mechanism which HTTP Server side applications, such as CGI (2) , can use to both store and retrieve information on the HTTP (2) side of the connection. Basically, Cookies can be used to compensate for the (4) nature of HTTP. The addition of a simple, persistent, client-side state significantly extends the capabilities of WWW-based (5) .

A. graphics B. processes C. scriptsD. texts
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