Cảm kháng \(Z_L=Lw=\dfrac{1}{\pi}\cdot100\pi=100\left(\Omega\right)\)

Dung kháng \(Z_C=\dfrac{1}{Cw}=\dfrac{1}{\dfrac{10^{-4}}{2\pi}\cdot100\pi}=200\Omega\)

\(\varphi=\varphi_u-\varphi_i=0-\dfrac{\pi}{4}=-\dfrac{\pi}{4}\)

\(tan\varphi=\dfrac{Z_L-Z_C}{R}\Leftrightarrow tan\dfrac{-\pi}{4}=\dfrac{100-200}{R}\Rightarrow R=100\left(\Omega\right)\)

a) Ta thấy N1 > N2  => đây là máy hạ áp.

b) \(\dfrac{N_2}{N_1}=\dfrac{U_2}{U_1}\Leftrightarrow\dfrac{250}{1000}=\dfrac{U_2}{500}\Rightarrow U_2=125\left(V\right)\)

Dung kháng \(Z_C=\dfrac{1}{Cw}=\dfrac{1}{\dfrac{10^{-4}}{\pi}\cdot100\pi}=100\left(\Omega\right)\)

Tổng trở \(Z=\sqrt{R^2+Z_C^2}=\sqrt{100^2+100^2}=100\sqrt{2}\left(\Omega\right)\)

Hệ số công suất \(cos\varphi=\dfrac{R}{Z}=\dfrac{100}{100\sqrt{2}}=\dfrac{\sqrt{2}}{2}\)

Dung kháng \(Z_C=\dfrac{1}{Cw}=\dfrac{1}{31,8\cdot10^{-6}\cdot100\pi}=100\left(\Omega\right)\)

Để \(P_{max}\Leftrightarrow R=R_0=\left|Z_L-Z_C\right|=100\left(\Omega\right)\)

Công suất \(P_{max}=\dfrac{U^2}{2\cdot R_0}=\dfrac{50^2}{2\cdot100}=12,5\left(W\right)\)

Bước sóng \(\lambda\)= v/f = 1,2/20= 0,06(m) = 6(cm).

Số điểm dao động với biên độ cực tiểu là -S1S2 < (k+0,5)\(\lambda\) < S1S2.

\(\Leftrightarrow\) -3,51 < k < 2,51 => Có 6 giá trị của k dao động với biên độ cực tiểu.

1.exercise should not be seen as a demanding task (demand)

2. doctors have become increasingly worried about his statement. ( increase)

Sự nâng cấp quá chỉn chu và thành công ^^

Em có một số góp ý tại inbox, mong có thể giúp được gì đó cho web! 

Btw, congratulations ^^!

Y/c đề bài là present perfect passive nhưng các câu dẫn lại chèn thì simple past vào? Và nếu viết các câu đó qua passive nghĩa cũng không rõ + câu cũng không đẹp. Đề này chắc hẳn là "rewrite using Present.P?"

^{A gift}

P/s: Câu 1 và 2 phần vần không được tốt. Nhiều câu vẫn còn gieo chưa phù hợp (VD 5-6...):(

1,

1, When I started to learn at this school, I need a lot of help, but now ……………all the subjects on my own

A, used to learn

B, used to learning

C, get used to learning

2, he ………. Several books a month, but he dosen’t have time anymore

A, was used to reading

B, used to read

C, got used to reading

3, we were surprised to see her driving, she …………. When we first met her

A, got used to driving

B, didn’t use to drive

C, was used to driving

4, don’t worry, it’s a simple program. You ……….. it in no time, I’m sure

A, are used to

B, will get used to

C, used to use

5, when I had to commute to school every day, I …………. Very early

A, used to getting up

B, used to get up

C, use to get up

6, I’m afraid I’ll never ………….. in this place. I simply don’t like it and never will

A, used to live

B, got used to living

C, get used to living

7, whenever we came to Coventry, we always ………….. in the Central Hotel. We loved it

A, used to play

B, got used to staying

C, get used to stay

8, when peter smith was the head of our office everything …………. Well organized. Now it’s total chaos here

A, got used to be

B, used to be

C, was used to being

9, mr lazy was shocked when he joined our busy company because he ……………. Doing much work every day

A, wasn’t used to

B, didn’t used to

C, used to

10, At first, the employees didn’t like the new open- space office, but in end they ……………… it

A, get used to

B, are used to

C, got used to

11, jim doesn’t have a girlfriend now but he …………..

A, didn’t use to

B, used to

C, was using to

13,I ………… to play football when I was young. I’m too old and fat to paly now

A, use

B, got used to

C, used

14, Nam was in London for a year. He likes England but he ………. The insipid food and the miserable weather

A, could ever get used to

B, could never get used to

C, can ever get used to

15, I’ve been getting up early every day for years but I …………… to it

A, used

B, am still not used

C, am already used

16, if you go to live in the united kingdom, you ……….. on the left

A, will have to get used to drive

B, will have to get used to driving

C, would have had to get used to

17,At fist, a was difficult for her to speak in French all the time but she ………….to it now

A, is used

B, uses

C, used

18, After the holidays, it takes me a week …….. up early again

A, to get used to getting

B, to be used to get

C, to get used to get

19, The queue in the baker’s ………….to be so bad but now it’s terrible. It must be that new chapata bread they bake. It’s delicious

A, didn’t use

B, didn’t used

C, was used

20, Do you mind if I ………..your phone?

A, used

B, am using

C, use