## Concours: Gagne à utiliser Alloprof cet été

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### Question de l’élève

Secondaire 5 • 1a

Hi, I’m trying to do this but the steps dont seem right, and I’m not sure what formula to use. Do i use P=E/Time? If so, how do I know what the Power is?

Physique

## Explications (1)

• Explication d'Alloprof

Explication d'Alloprof

Cette explication a été donnée par un membre de l'équipe d'Alloprof.

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Équipe Alloprof • 1a

Yes, P=E/time is a formula you could use to solve this problem. However, you will also need to use...

$$P = U•I$$

Legend :

• P : power (W)
• U : voltage (V)
• I : amperage (I)

...and also...

$$1\:W•1\:h = 3600\:J$$

...and finally...:

$$Q = mc∆T$$

Legend :

• Q : energy (J)
• m : mass (g)
• c : specific heat capacity (J/(g•°C))
• ∆T : temperature variation (°C)

Therefore, the solution to the problem should look like this :

1. First, find the power of the hot plate using P=UI. Don't forget to multiply the end result to take into account its energetic efficiency.
2. Next, find the energy required to bring the water to boiling point using Q = mc∆T. You may have to look around to find the quantity of water being boiled as well as its initial temperature. Remember that, for water, 1 mL = 1 g. The final value of Q is the same variable as E.
3. Finally, use P = E/t to determine the amount of time required to boil the water. Be careful to remember that 1 W = 1 h • 3600 J.

Don't hesitate to ask for more help!

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