Thermal energy into liquid

In summary, the immersion heater converts electrical energy into thermal energy that is transferred to the liquid it is immersed in. The thermal energy transferred in time t is given by I^2Rt, where I is the current and R is the resistance. This can be derived from the voltage drop across the resistance, V=IR, and the definition of current, I=dq/dt. Therefore, the correct answer is #2, I^2Rt.
  • #1
UrbanXrisis
1,196
1
An immersion heater of resistance R converts electrical energy into thermal energy that is transferred to the liquid in which the heater is immersed. If the current in the hearter is I, the thermal energy trasferred to the liquid in time t is?

1) IRt

2) I^2Rt

3) IR^2t

4) IRt^2

5) IR/t

The answer is #2 but I don't see how my book got that answer.
 
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  • #2
The voltage drop across a resistance R when the current is I is given by V=IR.
Note that voltage has units of energy/charge. Multiply the voltage by current, which has units charge/time, and you get the rate at which heat is generated in the resister, I^2R, the units being energy/time. If the current is steady, the total energy changed to the form of heat will just be that rate, I^2R, times the amount of time that you let the process run, that is: I^2 Rt.
 
  • #3
mgh also has units of energy, does that make it right as well? :smile:

Think of an electron as it goes through the resistor. Its speed doesn't change (since the current is constant) so what does change, and where is the heat coming from? Let's consider the energies of the electron - it has kinetic energy and electric potential energy. The former doesn't change, but the latter does. The 'lost' energy becomes heat:
ΔEk + ΔEp = ΔET
ΔEp = ΔVq = ET
So now we are looking to find the value of ΔVq. But what is q really? You might remember that current is defined as:
I = dq/dt
If we extract q from there we find that:
ΔET = ΔVq = VIt
We're almost done now... what's V then? Of course it's IR. So finally we get that:
ΔET = VIt = I^2Rt
Which is answer #2.
 
Last edited:

1. What is thermal energy?

Thermal energy is the energy that comes from the internal motion of particles in a substance. It is also known as heat energy and can be transferred from one object to another.

2. How does thermal energy turn into liquid?

Thermal energy can turn into liquid through a process called melting. When a substance reaches its melting point, the thermal energy breaks the bonds between molecules, causing them to move more freely and form a liquid state.

3. What happens to thermal energy when a liquid cools?

When a liquid cools, its thermal energy decreases. This causes the molecules to slow down and come closer together, eventually forming a solid state. The thermal energy is then stored as potential energy in the bonds between molecules.

4. Can thermal energy be converted into liquid without changing the substance?

No, thermal energy cannot be converted into liquid without changing the substance. The process of converting thermal energy into liquid involves breaking and forming bonds between molecules, which results in a change of state for the substance.

5. How is thermal energy into liquid used in everyday life?

Thermal energy into liquid plays a crucial role in everyday life. It is used in various applications such as cooking, heating water, and powering steam engines. It is also used in industries for processes such as distillation and evaporation.

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