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How long does it take to make 80kg water from 20 ℃ to 55 ℃ with the electric heater of "220V 1.8kw" fast
1.8kw is just the heating power of the heater. If you want to know how long it will take, you need to know its heat transfer efficiency
If the heat transfer efficiency is 100% (actually impossible), according to the formula q = C * m * Δ t (q is heat, C is specific heat capacity, M is mass, Δ t is temperature difference), q = 2800000 (J) can be calculated
And q = P * t (P is power, t is time), so the time t is about 1555.6 seconds, about 26 minutes
The resistance of a conductor is 10 ohm, in which the heat generated in 1 min is ()
Q=I²Rt=(0.5A)²*10Ω*60s=150J
A 5-ohm constant value resistor, given that the point current passing through it is 2a, how much heat is released in 1min? If the current passing through it is reduced to half of the original, how much heat is released in the same time?
1. According to the formula q = I ^ 2rt = (2a) ^ 2 * 60s * 5 Ω = 1200J
2. Two methods: ① 2 / 2 = 1a
Q=I^2RT=300J
②I^2:I'^2=Q:Q'
∴Q:Q'=4:1
So q = 300j
Resistance R1 = 15 ohm, R2 = 25 Ohm, the voltage at both ends of R1 is 9 V, calculate; one voltage at both ends of R2, two power supply voltage, three electric energy consumed by R1 and R2 within two minutes
series connection
Circuit current I = U1 / R1 = 9 / 15 = 0.6A
R2 terminal voltage U2 = I * R2 = 0.6 * 25 = 15V
Power supply voltage = U1 + U2 = 9 + 15 = 24 V
W1=P1*T=U1^2/R1*T=9*9/15*3*60=972J
W2=P2*T=U2^2/R2*T=1620J
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