Hey! Sign in to get help with your study questionsNew here? Join for free to post

A little help with part B?

Announcements Posted on
Would YOU be put off a uni with a high crime rate? First 50 to have their say get a £5 Amazon voucher! 27-10-2016
    • Thread Starter

    Thanks in advance
    Attached Images

    For a) I got the answer as D, which is equal to a resistance of 3.67\Omega
    For part b) you have the voltage generated at the power station, which is NOT the voltage in the cables- this electricity is being delivered somewhere and most of the voltage will be going to the city. Remember voltage is different at different points in a series circuit. You also have the power being produced at the power station (again, most of this is being dissipated in the city so this figure doesn't relate to the cables, it's at the source).

    The thing that stays constant in a series circuit is the current. The current at the power station can be calculated as I=P/V and we have both voltage and power at the power station.
     I=\frac{1 \times10^9}{400 \times10^3}.=2500A
    This gives the current in the whole circuit, including the cables which are what you're interested in. You now have resistance and current for the cables, so use
    P=I^2 R

P= 2500^2 \times 3.68 =23 \times 10^6 =23MW
    So I think the answer's D.
    • Thread Starter

    The answer is E according to the mark scheme, so i guess you need to double the last 23MW?

    Thanks for the help anyway, my mistake was in assuming it was a parallel circuit.

    Yes, of course, because there's two cables! Sorry about that.
Write a reply…


Submit reply


Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. Oops, you need to agree to our Ts&Cs to register
  2. Slide to join now Processing…

Updated: August 4, 2016
TSR Support Team

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.

Would you rather be able to

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.