Resistance of a water heaters heating element?

In summary, a water heater's heating element has a resistance of 120 V - 240 V = 60 W. It takes 4184 J to raise 1 kg of water 1°C.

Homework Statement

Household water heaters use a 240 V rather than a 120 V source. What is the resistance of a water heater's heating element if it heats 40 gallons (151 kg) of water from 15 C to 60 C in 15 min

P = IV
P = I^2R
I = dq/dt

The Attempt at a Solution

Honestly no clue. If anyone can give me some hints I would really appreciate this.

So far I have electrical units, V, and then I have kg, Celcius, and seconds. I'm not sure how the given equations help me relate the units at all.

I need current and power, but those units do not help me at all.

I know I = dq/dt, and I thought 45 C / 900 s looks very similar to current but the units don't make sense to me...

Do you know how to determine how much heat it takes to raise the temperature of 1 kg of water from 15 C to 60 C?

Chestermiller said:
Do you know how to determine how much heat it takes to raise the temperature of 1 kg of water from 15 C to 60 C?

I'm not sure actually.. this chapter that I'm studying is called Current and Resistance..

It has to do with specific heat, right? Also, does heat = thermal energy?

I'm not sure actually.. this chapter that I'm studying is called Current and Resistance..

It has to do with specific heat, right? Also, does heat = thermal energy?
Yes. Did you not study heat in freshman physics?

Chestermiller said:
Yes. Did you not study heat in freshman physics?

I don't think I studied it enough..

So if the specific heat of water is 4.187 x 10^3 J/(kg * k )

That means it requires 4.187 x 10^3 J to raise 1 kg of water by 1 kelvin, correct?

I'm not sure actually.. this chapter that I'm studying is called Current and Resistance..

It has to do with specific heat, right? Also, does heat = thermal energy?
Yes, heat = thermal energy. To raise a kg water 1°C, you need 4184 Joules of heat (thermal energy).

What is the mass in kg of 40 gallons of water?

Last edited:
Chestermiller said:
What is the mass in kg of 40 gallons of water?

Anyhow, using the heat you can now calculate the power (J/s). See that the heat is the 'J' and the time you have the 's'.

Now think about how you can get current!

1. What is the purpose of measuring the resistance of a water heater's heating element?

Measuring the resistance of a water heater's heating element is important in determining the health and efficiency of the element. It can also help in troubleshooting any issues with the heating element or the overall functioning of the water heater.

2. How is the resistance of a water heater's heating element measured?

The resistance of a water heater's heating element is typically measured using a multimeter. The multimeter is set to the resistance or ohms setting, and the probes are connected to the terminals of the heating element. The resistance reading on the multimeter will indicate the health of the element.

3. What is the expected resistance of a functioning water heater's heating element?

The expected resistance of a functioning water heater's heating element can vary depending on the type and size of the element. Generally, a healthy heating element will have a resistance range of 10-16 ohms, but it is best to consult the manufacturer's specifications for the specific element being tested.

4. What does a high or low resistance reading indicate for a water heater's heating element?

A high resistance reading on a water heater's heating element can indicate that the element is damaged or failing. This can result in the element not heating up the water properly. On the other hand, a low resistance reading can indicate a short circuit in the element, which can also cause issues with the water heater's performance.

5. Are there any safety precautions to take when measuring the resistance of a water heater's heating element?

Yes, it is important to take safety precautions when measuring the resistance of a water heater's heating element. Make sure to turn off the power supply to the water heater and wait for it to cool down before attempting to measure the resistance. Also, wear protective gear, such as gloves and safety glasses, to prevent any accidents or injuries.

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