2 Simple G.C.S.E. questions.

1. Jun 17, 2012

Ryanzmw

1. The problem statement, all variables and given/known data

Here is the first of the two questions:

1.
"The overall efficiency of a power station can be increased by using the waste energy it generates to warm neary buildings. This is called Combined Heat and Power (CHP).
i) Suggest why not all power stations are part of a CHP sceme.
(1 mark)

Heres the second question:

2.
"Electric cars are far more efficient at transferring electrical energy into kinetic energy than petrol cars are at transferring potential chemical energy into kinetic. This view ignores where the electrical energy comes from in the first place. Taking this view into account the differerence is not as big at it seems at first. Explain why electric cars are not necessarily quite as efficient as they seem at first." (4 marks)

3. The attempt at a solution

1.

Firstly most power stations are located in fairly remote location and don't have the need for powering several buildings. Secondly this kind of heat channeling would be fairly expensive to set up.

2.
Electric cars appear more efficient than petrol cars when considering only the final energy transfer to kinetic energy as electric cars generally make very little noise. However to consider the true efficiency of an electric cars you must consider the efficiency of the power plant where the electricity used to power the car was generates. When this is considered the electric car appears not much more efficient than a petrol powered car. One factor making electric cars less efficient is the high number of energy transfers between the inital burning of the fuel in the power plant and the kinetic energy of the car.

Would these 2 answers give me all the marks, or how could I improve my answers.

2. Jun 17, 2012

BruceW

They both look like pretty good answers to me. I think you have got the main points. In GCSE questions, they are looking for particular points (and of course, you need to set them out in a readable way, which you have done). So for your second answer, If I were marking it, I would look at the points like this:
-appear efficient when considering final transfer.
-true efficiency is affected by efficiency of power plant.
-this makes electric car not much more efficient that a petrol car.
-high number of energy transfers makes electric car less efficient.

I think these are some pretty good points, but I'm not certain if they would each get you a mark. I think it helps if you look over past mark schemes for gcse exams. Are these questions from past exam papers?

There is always the controversy between actually learning the physics, and learning how to do well in the exam. The best thing you can do is to learn the physics and learn how to do well in the exam.