Ba tu mac noi tiep nen dien tich tren moi tu la nhu nhau

C1 = 2 x 10 mu -9 F

C2 = 4 x 10 mu -9 F

C3 = 6 x 10 mu -9 F

Tinh dien dung tuong duong

1 chia C = 1 chia C1 + 1 chia C2 + 1 chia C3

= 1 chia 2 + 1 chia 4 + 1 chia 6 tat ca nhan 10 mu 9

Quy dong

= 6 12 + 3 12 + 2 12

= 11 12

Suy ra

1 chia C = 11 chia 12 nhan 10 mu 9

C = 12 chia 11 nhan 10 mu -9 F

Khi dat U = 1100 V

Dien tich Q = C U

Q = 12 chia 11 nhan 10 mu -9 nhan 1100

= 1,2 x 10 mu -6 C

Hieu dien the moi tu

U1 = Q chia C1 = 1,2 x 10 mu -6 chia 2 x 10 mu -9 = 600 V

U2 = Q chia C2 = 1,2 x 10 mu -6 chia 4 x 10 mu -9 = 300 V

U3 = Q chia C3 = 1,2 x 10 mu -6 chia 6 x 10 mu -9 = 200 V

Tu 1 chiu 600 V lon hon 500 V nen bi vuot qua gioi han

Ket luan

Bo tu khong chiu duoc 1100 V vi tu C1 bi qua dien ap 600 V lon hon 500 V

Ta co dien the tai khoang cach r la

V = kQ chia r

Voi k bang 9 x 10 mu 9

Tai M voi r1 bang 1 m

VM = kQ chia 1 = kQ

Tai N voi r2 bang 2 m

VN = kQ chia 2

Hieu dien the UMN = VM tru VN

UMN = kQ tru kQ chia 2

UMN = kQ chia 2

Do do

UMN = kQ chia 2

b

Voi Q = 8 x 10 mu -10 C

UMN = 9 x 10 mu 9 nhan 8 x 10 mu -10 chia 2

= 72 x 10 mu -1 chia 2

= 7,2 chia 2

= 3,6 V

Cong cua luc dien khi electron di tu M den N

A = q UMN

Dien tich electron q = -1,6 x 10 mu -19 C

A = -1,6 x 10 mu -19 nhan 3,6

= -5,76 x 10 mu -19 J

Neu hoi cong can thuc hien thi do lon la

5,76 x 10 mu -19 J

Ta co

E = 1000 V m

v0 = 3 x 10 mu 5 m s

m = 9,1 x 10 mu -31 kg

e = 1,6 x 10 mu -19 C

Electron mang dien tich am nen luc dien truong gay gia toc nguoc chieu chuyen dong lam no cham dan roi dung lai

Dung dinh luat bao toan dong nang

mot phan hai m v0 binh phuong bang e E s

Suy ra

s = m v0 binh phuong chia 2 e E

Thay so

v0 binh phuong = 9 x 10 mu 10

m v0 binh phuong = 9,1 x 10 mu -31 nhan 9 x 10 mu 10

= 8,19 x 10 mu -20

2 e E = 2 nhan 1,6 x 10 mu -19 nhan 1000

= 3,2 x 10 mu -16

s = 8,19 x 10 mu -20 chia 3,2 x 10 mu -16

xap xi 2,56 x 10 mu -4 m

Ket qua

s xap xi 2,6 x 10 mu -4 m