As shown in the figure, it is the working principle circuit diagram of the household rice cooker. The working voltage is U=220V, and it is heated by R 1 and R2. When the switch is known to be closed,

As shown in the figure, it is the working principle circuit diagram of the household rice cooker. The working voltage is U=220V, and it is heated by R 1 and R2. When the switch is known to be closed, r 1 = R2 = 44ω, (1). (1) When the switch is closed and R 1 is short-circuited, the total power of the rice cooker is:

p 1 = u2r 2 = 220244 w = 1 100 w

(2) When the switch is off, R 1 and R2 are connected in series, and the current in the circuit is I = ur1+R2 = 22044+44a = 2.5a.

Then the total power of the rice cooker is p2 = I2 (r1+R2) = 2.52× 88w = 550w.

(3) As can be seen from the above calculation, the switch is insulated when it is turned off.

Answer: (1) When the switch is closed, the total power of the rice cooker is 1 100 w(2) When the switch is closed, the total power of the rice cooker is 550 w(3) If the rice cooker is kept warm, the switch is closed.