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Reading:Silicon Valley staff tuck into Lunch 2.0 Even the millionaire engineers of Silicon Valley, the centre of computer technology in the USA like to have a free lunch. There is an interesting new idea in Silicon valley called Lunch 2.0. Workers go to other companies for free food and the chance to make new contacts. It started with four men trying to get into companies such as Yahoo and Google to sample their free gourmet lunches. But the idea is so successful that several companies now invite anyone for a free lunch. Except, of course,it is not really free. The lunches are partly about networking and eating, but they are also about presenting products and looking for new staff. In the latest example, more than 100 people turned up for lunch at the offices of Ning, a web company, in Palo Alto last week. They had sandwiches, salad, cookies -- and a presentation by Gina bianchini, Chief Executive. David Kellogg, a Yahoo technician and one of the people who started Lunch 2.0, said: “There's a business side and a food side to this.” He says lunch at the LinkedIn social networking company is the best so far.
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【单选题】三个交流电压的解析式分别为 u 1 = 20sin(100 t + π / 6)V , u 2 = 30sin(100 t + 90 ° )V , u 3 = 50sin(100 t + 2 π / 3)V 。下列答案中正确的是 ( )
A.
u 1 比 u 2 滞后 60°
B.
u 1 比 u 2 超前 60°
C.
u 2 比 u 3 超前 20°
D.
u 3 比 u 1 滞后 150 °
【单选题】三个交流电压的解析式分别为 u 1 = 20sin(100 t + π / 6)V , u 2 = 30sin(100 t + 90°)V , u 3 = 50sin(100 t + 2π / 3)V 。下列答案中正确的是 ( )
A.
比 2 滞后60 °
B.
1 比 超前60 °
C.
u 2 比 u 3 超前 20°
D.
u 3 比 u 1 滞后 150°
【简答题】案例： 下面是教师在“电功率”一课中。向学生讲解纯电阻的电功率的教学片段。 教师：同学们。我们已经学习过功率的概念，请大家说一下它的定义。 学生：功率就是单位时间所做的功或消耗的能量。 教师：对．今天我们推导阻值为R的电阻的功率。 教师：功率的公式为P＝W／t，通过焦耳定律，推出了纯电阻的电功率的表达式：P＝I2R，P＝U2／R .对这三个公式，教师分别讲解。指出哪个是定义式，哪个是计算式。 学生...
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