Thermal Energy and Heat Transfer

In summary, using the provided givens and the formulas for energy transfer, it would take approximately 6.2 minutes for a 1000W electric kettle to bring 1.0L of water to the boiling point from an initial temperature of 15ºC while being made of 400g of iron, assuming no heat is lost and the kettle is 100% efficient.
  • #1
richievuong
35
0
Question:

How long does it take a 1000W electric kettle to bring 1.0L of water to the boiling point if the initial temperature of the water is 15ºC and the kettle is made of 400g of iron?

Assume that no water is boiled, that no heat is lost to the surroundings, and that the kettle is 100% efficient.

Well first thing I did of course is write givens:
Temperature(water, initial) - 15ºC
Temperature(water, final) - 100ºC
Specific Heat Capacity (water) - 4200 J/kgºC
Specific Heat Capacity (iron) - 460J/kgºC
Mass (iron) - 0.4kg
Mass water - 1.0L = 1kg
Power of kettle - 1000W

I know the p= W/T and e=mct formulas but I'm having trouble with applying the 1000W to the heat transfer formulas. The other questions I've done,only required me to do mcΔt = -mcΔt with some latent fusion/vapourization in there.

Confused where to start...
 
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  • #2
richievuong said:
Question:

How long does it take a 1000W electric kettle to bring 1.0L of water to the boiling point if the initial temperature of the water is 15ºC and the kettle is made of 400g of iron?

Assume that no water is boiled, that no heat is lost to the surroundings, and that the kettle is 100% efficient.

Well first thing I did of course is write givens:
Temperature(water, initial) - 15ºC
Temperature(water, final) - 100ºC
Specific Heat Capacity (water) - 4200 J/kgºC
Specific Heat Capacity (iron) - 460J/kgºC
Mass (iron) - 0.4kg
Mass water - 1.0L = 1kg
Power of kettle - 1000W

I know the p= W/T and e=mct formulas but I'm having trouble with applying the 1000W to the heat transfer formulas. The other questions I've done,only required me to do mcΔt = -mcΔt with some latent fusion/vapourization in there.

Confused where to start...
Find how much energy is needed to bring the temperature of the water and iron kettle from 15ºC to 100ºC . Then work out how long it would take to deliver that energy at 1000 Joules/sec.

AM
 
  • #3
oh well now i kind of figured that

|E heat lost| = |E heat gained|
so e = mcΔt
e= (1)(4200)(100-15)
e= 357000

p=W/T
1000W = 357000J/T
T = 357s (5.9mins)

answer said 6.2...either I'm missing some steps, or I'm just completely wrong...i didn't fit in the stuff for iron...

EDIT: haha nvm i figured it out
e = mcΔt
e = (0.4)(460)(100-15)
e(iron) = 15640 + 357000 = 372640J/1000= 372.64 (6.2mins)

thanks anyway
 
Last edited:

FAQ: Thermal Energy and Heat Transfer

1. What is thermal energy and how is it different from heat?

Thermal energy is the total energy of all the particles in a substance. It includes both the kinetic energy (motion) and potential energy (position) of the particles. Heat, on the other hand, refers to the transfer of thermal energy from one substance to another.

2. How is thermal energy transferred between objects?

Thermal energy can be transferred through three main mechanisms: conduction, convection, and radiation. Conduction occurs when two objects are in direct contact and heat is transferred through molecular collisions. Convection refers to the transfer of heat through the movement of fluids or gases. Radiation refers to the transfer of heat through electromagnetic waves.

3. What is the difference between specific heat and heat capacity?

Specific heat refers to the amount of heat required to raise the temperature of 1 gram of a substance by 1 degree Celsius. Heat capacity, on the other hand, refers to the amount of heat required to raise the temperature of an entire substance by 1 degree Celsius. It is calculated by multiplying the specific heat by the mass of the substance.

4. How does insulation affect heat transfer?

Insulation is a material that is used to reduce the rate of heat transfer. It works by trapping air pockets, which are poor conductors of heat, and preventing the transfer of heat through conduction or convection. Insulation can significantly reduce the amount of heat lost or gained by a substance, making it an important component in maintaining energy efficiency.

5. How is thermal energy used in everyday life and industry?

Thermal energy is used in a variety of ways in everyday life and industry. Some common uses include heating homes and buildings, cooking food, generating electricity, and powering vehicles. In industry, thermal energy is used for processes such as melting and molding metals, processing food and beverages, and powering machinery.

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