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# Electricity power/energy Q

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I'm not sure how 2a is different from 2b.

The mark scheme uses E = VIt = Pt for part A (1200J)

For part B, it uses E(lost) = I^2t = Pt for part B (46J)

So using the power formula, P = VI = I^2R = V^2/R, why aren't the answers the same?

Kind regards,

Kevin
2. (Original post by TheKevinFang)
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I'm not sure how 2a is different from 2b.

The mark scheme uses E = VIt = Pt for part A (1200J)

For part B, it uses E(lost) = I^2t = Pt for part B (46J)

So using the power formula, P = VI = I^2R = V^2/R, why aren't the answers the same?

Kind regards,

Kevin
I'm not too sure what you're asking, but the energy transferred by the battery will not all be lost in the connecting wires and some will be lost in the motor instead.

So you have 1200J of energy produced by the battery, which is (a). But (b) just asks how much is lost in the connecting wires and, by the conservation of energy, will not be 1200J, as energy will be lost in other places too.
3. (Original post by kingaaran)
I'm not too sure what you're asking, but the energy transferred by the battery will not all be lost in the connecting wires and some will be lost in the motor instead.

So you have 1200J of energy produced by the battery, which is (a). But (b) just asks how much is lost in the connecting wires and, by the conservation of energy, will not be 1200J, as energy will be lost in other places too.
Hi,

Thanks for the reply. Why is the energy lost for (b) I^2R? Could you explain please?
4. (Original post by TheKevinFang)
Hi,

Thanks for the reply. Why is the energy lost for (b) I^2R? Could you explain please?
Well energy = power * time

Power = IV = I^2R = V^2/R.

If you know all three, you can use any of them and you'll get the same answer, but in this case you don't know all three. You don't know the voltage across the connecting wires (you know the voltage across the battery).

You only know the amount of current that flows through the wires and the resistance of them, so P=I^2R is most appropriate here. Then you multiply this by the time.

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The text passage is a discussion from a physics forum where a student is asking for clarification on the difference between two parts of a question related to electrical energy and power. Another user provides an explanation.
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the passage does not contain a direct mathematical question that requires a numerical answer. instead, it contains a conceptual question about the application of formulas in a physics problem, and an explanation is provided.
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TYPE: <one of the following values>
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- MULTIPLE_QUESTIONS
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You are Here: Home >< Physics

# Electricity power/energy Q

Announcements Posted on
Last day to win £100 of Amazon vouchers - don't miss out! Take our quick survey to enter 24-10-2016
1. https://onedrive.live.com/redir?resi...nt=photo%2cJPG

I'm not sure how 2a is different from 2b.

The mark scheme uses E = VIt = Pt for part A (1200J)

For part B, it uses E(lost) = I^2t = Pt for part B (46J)

So using the power formula, P = VI = I^2R = V^2/R, why aren't the answers the same?

Kind regards,

Kevin
2. (Original post by TheKevinFang)
https://onedrive.live.com/redir?resi...nt=photo%2cJPG

I'm not sure how 2a is different from 2b.

The mark scheme uses E = VIt = Pt for part A (1200J)

For part B, it uses E(lost) = I^2t = Pt for part B (46J)

So using the power formula, P = VI = I^2R = V^2/R, why aren't the answers the same?

Kind regards,

Kevin
I'm not too sure what you're asking, but the energy transferred by the battery will not all be lost in the connecting wires and some will be lost in the motor instead.

So you have 1200J of energy produced by the battery, which is (a). But (b) just asks how much is lost in the connecting wires and, by the conservation of energy, will not be 1200J, as energy will be lost in other places too.
3. (Original post by kingaaran)
I'm not too sure what you're asking, but the energy transferred by the battery will not all be lost in the connecting wires and some will be lost in the motor instead.

So you have 1200J of energy produced by the battery, which is (a). But (b) just asks how much is lost in the connecting wires and, by the conservation of energy, will not be 1200J, as energy will be lost in other places too.
Hi,

Thanks for the reply. Why is the energy lost for (b) I^2R? Could you explain please?
4. (Original post by TheKevinFang)
Hi,

Thanks for the reply. Why is the energy lost for (b) I^2R? Could you explain please?
Well energy = power * time

Power = IV = I^2R = V^2/R.

If you know all three, you can use any of them and you'll get the same answer, but in this case you don't know all three. You don't know the voltage across the connecting wires (you know the voltage across the battery).

You only know the amount of current that flows through the wires and the resistance of them, so P=I^2R is most appropriate here. Then you multiply this by the time.

## Register

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Updated: May 13, 2016
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We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

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Today on TSR

### How does exam reform affect you?

From GCSE to A level, it's all changing

### Q&A with Paralympian Jack Rutter

Poll
Study resources

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.
user
The text passage is a discussion from a physics forum where a student is asking for clarification on the difference between two parts of a question related to electrical energy and power. Another user provides an explanation.

TYPE: NO_QUESTION

The passage does not contain a direct mathematical question that requires a numerical answer. Instead, it contains a conceptual question about the application of formulas in a physics problem, and an explanation is provided.