# Energy conversions - wind up radio

1. Dec 9, 2008

### dukg08

1. The problem statement, all variables and given/known data
(a) The wind-up radio is a wonderful example of the process of energy transformation from one type to another. The radio is operated as follows:
(i)
The user turns a handle that winds a metal spring onto a spool.
(ii)
The metal spring then unwinds slowly, through a number of gears, rapidly turning the spindle of a small electrical generator.
(iii) The electrical generator feeds a rechargeable battery.
(iv)
When the radio is turned on, it is powered from the battery.
(v)
Sound is produced by the vibrating diaphragm in the radio’s loudspeaker.

Based on the information in (i)–(v), list the energy transfers and conversions which take place in the process described above, from the user initially turning the handle through to the sound being produced by the radio. You should give your answer as a series of points and in each point you should clearly identify the stage you are describing and the energy transfers and/or conversions that are taking place. We expect you will be able to answer part (a) in around 200 words.

2. Relevant equations
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3. The attempt at a solution

(i)
The user turns a handle that winds a metal spring onto a spool. - chemical energy in the body to kinetic energy in turning the handle to strain potential energy
(ii)
The metal spring then unwinds slowly, through a number of gears, rapidly turning the spindle of a small electrical generator. not sure what energy/conversion this all has except it's some sort of movement - mechanical energy
(iii) The electrical generator feeds a rechargeable battery. mechanical energy in to stored electrical energy
(iv)
When the radio is turned on, it is powered from the battery. kinetic energy to electrical energy
(v)
Sound is produced by the vibrating diaphragm in the radio’s loudspeaker. electrical energy into something into sound energy

I'm not totally sure I'm on the right track with this. Obviously I will re-write this.

Last edited: Dec 9, 2008
2. Dec 9, 2008

### Lyuokdea

the first part sounds right...i might just call it "spring potential energy", i don't know what your book calls it....

remember that on every step, the energy has to come from somewhere. In this case, it will always be coming from where it was added in the last section... that should help you on the rest...

I would also call energy in a battery "chemical energy", as it's very similar to what your body is doing when it stores energy in ATP.

Good luck,

~Lyuokdea

3. Dec 10, 2008

### dukg08

so would this be better:

(i)
The user turns a handle that winds a metal spring onto a spool. - chemical energy in the body to kinetic energy in turning the handle to spring potential energy
(ii)
The metal spring then unwinds slowly, through a number of gears, rapidly turning the spindle of a small electrical generator. Spring potential energy to mechanical energy to stored electrical energy
(iii) The electrical generator feeds a rechargeable battery. stored electrical energy to chemical energy
(iv)
When the radio is turned on, it is powered from the battery. Chemical energy to electrical energy (v)
Sound is produced by the vibrating diaphragm in the radio’s loudspeaker. Electrical energy into sound energy

4. Dec 10, 2008

### brewnog

For part (ii), do you think the middle stage might be better described as kinetic energy, what with the movement of the gears and generator shaft? Also, do you think the last conversion in this step would be to electrical energy; you don't store it until step (iii).

For part (v), this is basically correct, but have a think about how the sound energy is actually produced.

Last edited: Dec 10, 2008
5. Dec 10, 2008

### dukg08

So the battery would be ‘stored electrical energy’? What is the generator then?
(iv) can’t be right if the battery is ‘stored electrical energy’ can it?
Is (iii) the wrong way round?

6. Dec 10, 2008

### brewnog

Well a battery stores electrical energy as chemical energy. So you could call the energy in the battery "stored electrical energy" or "chemical energy". But the energy produced by the generator is "electrical energy". I'd say that (iii) is "electrical energy to chemical energy". It's semantics. Your description of (iv) looks good, so just reverse it for (iii).

7. Dec 10, 2008

### dukg08

so the following:

(i)
The user turns a handle that winds a metal spring onto a spool. - chemical energy in the body to kinetic energy in turning the handle to spring potential energy
(ii)
The metal spring then unwinds slowly, through a number of gears, rapidly turning the spindle of a small electrical generator. Spring potential energy to kinetic energy to electrical energy
(iii) The electrical generator feeds a rechargeable battery. electrical energy to chemical energy
(iv)
When the radio is turned on, it is powered from the battery. Chemical energy to electrical energy
(v)
Sound is produced by the vibrating diaphragm in the radio’s loudspeaker. Electrical energy into sound energy - add more to this one

obviously rewording it to answer the question fully

8. Dec 10, 2008

### brewnog

Looks good.

How does the loudspeaker produce sound energy? Or, more pedantically, what is sound energy?

9. Dec 10, 2008

### dukg08

thats what I'm working on :)

It's all to do with waves I think

Last edited: Dec 10, 2008