People's Education Edition, the ninth grade, the second volume of physics, all-in-one study, practice test, chapter 18, chapter 2, power-saving answer.

Answer: self-study, thinking about problems [combing new knowledge]

I. Electricity

1. How fast is the current?

2. Watt Watt kW 1000

3. The title is abbreviated

(1) power-on time

(2)W/t UI

(3)U？ /R I？ rare

4. 1

Second, the rated power

1. Normal operation

2. Rated voltage

3.( 1)>(2)= normal luminescence (3)

( 1) ui (2) w/t

Interactive inquiry and problem solving

Example 1 D

Example 2

( 1)u 1 = IR 1 = 0.2A？ 24? =4.8V，P 1=U 1I=4.8V？ 0.2A = 0.96W watt.

(2)U2=IR？ =0.2A？ 36? =7.2V，U = U 1+U2 = 4.8V+7.2V = 12V，Ptotal =UI= 12V？ 0.2A=2.4W。

(3)W total =P total t=2.4W? 180s=432J .

Example 3 6.4

Example 4 C

Example 5 variant question b

Classroom summary, classroom test [classroom test]

1.BD 2。 D 3。 D

4. Electric energy 0.4

5. Short title

( 1)U = U2 = U 1 = I 1r 1 = 0.6A？ 10? =6V。

(2)I2=P2/U2=P2/U=2.4W/6V=0.4A，R2=U2/I2=6V/0.4A= 15？ ,

(3)P=U(I 1+I2)=6V？ (0.6A+0.4A)=6W，W=Pt=6W？ 100 second = 600 joules.

6.A

7. 1.25 watt 0.8 watt