(20 14? Xiaoxing designed an automatic control device for her own bath electric water heater, as shown in the figure. R 1 is a water heater.

From P=U2R (1), the resistance of electric water heater is:

R=U2 forehead p forehead = (220v) 21800w ≈ 26.9ω;

(2) When the water temperature is 60℃, the armature is attracted and the heating circuit is cut off. At this time, R1=10Ω,

The total resistance in the series circuit is equal to the sum of the individual resistances,

∴R total = r1+R2 =10ω+10ω = 20ω,

Current in relay coil:

I=U0R total = 6v20ω = 0.3a

(3) Heat absorbed by water:

Q suction = cm (t-t0)

=4.2× 103J/(kg？ ℃) × 50kg× (60℃-30℃)

= 6.3× 106j；

Since heat loss is not calculated, W=Q absorption,

Obtained by W=Pt, heating time:

t = WP = 6.3× 106j 1800 w = 3500s。

So the answer is: (1) 26.9; (2)0.3; (3)3500.