a)Số electron thừa ở quả cầu A là:

\(N_1=\dfrac{4,8\cdot10^{-7}}{1,6\cdot10^{-19}}=3\cdot10^{12}\left(e\right)\)

Số electron thừa ở quả cầu B là:

\(N_2=\dfrac{4\cdot10^{-7}}{1,6\cdot10^{-19}}=2,5\cdot10^{12}\left(e\right)\)

Lực tương tác điện:

\(F=k\cdot\dfrac{\left|q_1q_2\right|}{r^2}=9\cdot10^9\cdot\dfrac{\left|-4,8\cdot10^{-7}\cdot4\cdot10^{-7}\right|}{0,15^2}=0,0768N\)

b)Cho hai quả cầu tiếp xúc điện với nhau rồi đặt về chỗ cũ thì điện tích mới của quả cầu là: \(q=\dfrac{q_1+q_2}{2}=\dfrac{\left|-4,8\cdot10^{-7}\right|+\left|4\cdot10^{-7}\right|}{2}=4,4\cdot10^{-7}\left(C\right)\)

 Lực tương tác điện giữa hai quả cầu sau đó là:

\(F=k\cdot\dfrac{q^2}{r^2}=9\cdot10^9\cdot\dfrac{\left(4,4\cdot10^{-7}\right)^2}{0,15^2}=0,07744N\)

câu b em tính chưa đúng nha, khi cho 2 quả cầu tiếp xúc nhau thì chúng trung hòa về điện, nhưng tính điện tích mỗi quả cầu như vậy thì sai

a. Điện trở tương đương mạch ngoài là: 

\(R_{tđ}=R_1+\dfrac{R_2R_3}{R_2+R_3}=11\left(\Omega\right)\)

Cường độ dòng điện chạy trong mạch là: 

\(I=\dfrac{\varepsilon}{r+R_{tđ}}=1\left(A\right)\)

Hiệu điện thế hai đầu điện trở \(R_1,R_2,R_3\) lần lượt là:

\(U_1=IR_1=6\left(V\right)\)

\(U_2=U_3=\varepsilon-Ir-U_1=5\left(V\right)\)

b. Điện năng tiêu thụ của mạch ngoài trong 10 phút là:

\(A=UIt=I^2R_{tđ}t=6600\left(J\right)\)

Công suất tỏa nhiệt ở điện trở \(R_1,R_2,R_3\) lần lượt là:

\(P_1=U_1I=6\left(W\right)\)

\(P_2=U_2I_2=\dfrac{U^2_2}{R_2}=2,5\left(W\right)\)

\(P_3=U_3I_3=\dfrac{U^2_3}{R_3}=2,5\left(W\right)\)

c. Công của nguồn điện sản ra trong 10 phút là: \(A=Pt=\varepsilon It=7200\left(J\right)\)

Hiệu suất của nguồn điện: \(H=\dfrac{A_{ci}}{A_{tp}}.100\%\approx92\%\)

a)\(R_{23}=\dfrac{R_2\cdot R_3}{R_2+R_3}=\dfrac{10\cdot10}{10+10}=5\Omega\)

\(R_{TĐ}=R_1+R_{23}=4+5=9\Omega\)

\(I=\dfrac{\xi}{R+r}=\dfrac{10}{9+1}=1A\)

\(U_1=I_1\cdot R_1=1\cdot4=4V;U_2=U_3=I_3\cdot R_3=1\cdot10=10V\)

b)\(A=UIt=\left(4+10\right)\cdot1\cdot10\cdot60=8400J=8,4kJ\)

\(P_1=U_1I_1=4\cdot1=4W;P_2=P_3=\dfrac{U_2^2}{R_2}=\dfrac{10^2}{10}=10W\)

Công suất bàn ủi là:
     P= U.I= 220 . 5 = 1100 (W)
Đổi 15 phút = 900s
Điện năng tiêu thụ trong 30 ngày là:
     A= P . t30 ngày=  1100. (900 . 30) = 29 700 000 J = 8,25 KWh
 Tiền điện phải trả cho việc sử dụng bàn ủi này trong 30 ngày là:
    8,25 . 1600= 13200 đồng

                       đáp số : 13200 đồng

tiếc quá mik ms hok lớp 7

easy như lớp 1

haha

hello.what you name

Viet Nam has gained three main benefits since it joined different international organisations. Firstly, it is easier and more convenient for Viet Nam to promote its culture and learn about other cultures. For example, various cultural exchanges help foreigners know more about our country. In addition, Vietnamese people have a better chance of experiencing different cultures. Secondly, this has created greater education opportunities for both Vietnamese and foreign students. More education opportunities abroad are now open to Vietnamese students. Viet Nam's colleges and universities can also accept international students. Finally, joining these organisations has also helped Viet Nam increase both local and international tourism. In fact, Viet Nam has become one of the most popular destinations for many foreign tourists in the region. It is also easier for Vietnamese people to travel abroad. In short, Viet Nam has benefited greatly from becoming a member of different international organisations.

The surgeon's job is traditionally most common for men. Surgeons have to perform operations on patients. They also have to make important decisions about patients' health and safety. Besides medical knowledge, surgeons need both physical and mental strength to perform long and tiring operations. In addition, surgeons need to have excellent eyesight and skilful hands. A surgeon works with a team, so he / she needs good teamwork and communication skills. Although it is traditionally seen as a male job, the number of women surgeons is increasing now. Women as mentally strong as men, and they can perform long operations. In summary, women can make great surgeons, and everybody will benefit from having both male and female surgeons.

The surgeon's job is traditionally most common for men. Surgeons have to perform operations on patients. They also have to make important decisions about patients' health and safety. Besides medical knowledge, surgeons need both physical and mental strength to perform long and tiring operations. In addition, surgeons need to have excellent eyesight and skilful hands. A surgeon works with a team, so he / she needs good teamwork and communication skills. Although it is traditionally seen as a male job, the number of women surgeons is increasing now. Women as mentally strong as men, and they can perform long operations. In summary, women can make great surgeons, and everybody will benefit from having both male and female surgeons.

t

Florence Nightingale is most famous for being the founder of modern nursing.

She was born in 1820 in Florence, Italy. She grew up in England with her parents and older sister. In 1844, she studied nursing in Germany and later went to London to work in a hospital. In 1854, Florence went to the military hospital in Scutari, Turkey, with 38 other women. They cleaned the hospital and improved conditions for the wounded soldiers. The death rate dropped from sixty percent to two percent within six months. In 1855, Queen Victoria gave Florence an award and a piece of jewelry. Florence wrote Notes on Nursing in 1859 and in 1860, she opened St. Thomas' Hospital where she started the Nightingale Training School for Nurses. In 1908, she was given the merit of honor by King Edward VII. She died two years later in London. Florence Nightingale will be remembered for being the founder of modern nursing.

x>y

hết 

s

o

s

ss

s

s

s

s

sssssssssssssssss

s

s

e

x

x

x

xx

x

x

x

Đáp số : X > Y