Electricity Questions Please Help?

part(i) is right, But remember watts is joules per second, that should enable you to answer the last part of the question also. How many seconds in 15 hours?

Reply 2

OP

Thanks for the reply, 60 x 60 x 15 = 54000s

(iii) 1080000W x 54000s =

Unparseable latex formula:

5.832x10^1^0 J s^-^1

Am i right here :confused:

what about part (ii) any ideas?

Reply 3

luap

Thanks for the reply, 60 x 60 x 15 = 54000s

(iii) 1080000W x 54000s =

Unparseable latex formula:

5.832x10^1^0 J s^-^1

Am i right here :confused:

what about part (ii) any ideas?

Yeah I think that is the answer for amount of energy in joules used in 15 hours. It should just be a joules answer though.

Unparseable latex formula:

5.832x10^1^0 J

(ii) Looks fine to me too but the exponent needs a change of sign.That resistance is huge :smile:

it's .000033 ohms not 33000 ohms.

3.3x10^{-5}

Reply 4

OP

Thanks dude your quite right, i made an edit earlier which i fooooked up thanks again for all your help.
Regards
luap. :wink:

Reply 5

OP

Can you help with this question? it seems quite simple but just to cover my arse!

The electricity cost is critical for the final price of the aluminium. What cost per kWh of electricity is acceptable if the company wishes to restrict the electricity cost to £200 per tonne or less?

One would assume that you simply divide £200 by 15 hours? About £13 per kWh to give £195 per tonne.

Any suggestions??

Regards
Luap.

Reply 6

That sounds fine by me I'd give the answer as about £13.33 though. Just to be accurate.

It's pretty clear why a fairly abundant element like Aluminium is relatively expensive though. 6v at 180000 A :/ smoking boots if you got zapped by that. :smile:

Reply 7

Sycren

11

for part i

the units is already kilowatt hours as powe is measured in watts and your time is larger than an hour.

Reply 8

Sycren

for part i

the units is already kilowatt hours as powe is measured in watts and your time is larger than an hour.

His answer is in watts not kW hours, to present a kWh answer is fairly simple too obviously; in a second though his answer is correct, Watts=J/s. I suppose it depends how you want to interpret the question but I don't think it mentions the answer has to be in kWh but it's simple to convert it anyway. And for 15 hours it's the same as kWh as it is for Joules per hour, but maybe I'm misinterpreting the question?

1W=1\frac{J}{s}

1080000W=1080000 J/s

Reply 9

Theorist

10

The energy in one kilowatt-hour is:

E = P\,t = 1000\times 60^{2} = 3.6\times 10^{6}\,\mathrm{J}.

That should help. :smile:

Reply 10

Yeah if you want to convert it into kW hours? I suppose, but I'm kind of confused why people are obsessing over KwH when the question doesn't ask you to express it in a particular unit form? Anyway it's pimply to do it either way. Mind you I haven't done physics in five years, so it's probably just a convention. Anyway your answers are all correct as far as I can see.

Reply 11

OP

Thanks for all your reply's, im going to stick with Watts as i believe this is what the question is asking.

Can you plesase help with this question??

Domestic aluminium foil for food use is

Unparseable latex formula:

15 x 10^-^6 m

thick. In my local supermarket, a roll of foil measuring 12 m by 0.5 m costs £2.29.

(i) Calculate the cost per tonne of foil as purchased in the supermarket.
Account for any difference between this cost and the raw material cost of £1200 per tonne.

The density of aluminium is

Unparseable latex formula:

2700 kg m^-^3

Once again i thank you for your help.
Regard's
Luap.

Reply 12

Luap something tells me you should of paid more attention in class. :smile:

Think what this is asking here, it's asking you to work out how many rolls of tin foil in one tonne and then to compare prices. You have all the information there you need.

What does density =.

Reply 13

OP

You may have a point, but on these particular questions im unsure on the answers and that is why im asking, that said your entitled to have your say.

Reply 14

luap

You may have a point, but on these particular questions im unsure on the answers and that is why im asking, that said your entitled to have your say.

Oh I didn't mean to slight you, I was only kidding sorry :smile:

But think about what I said? density=mass/volume right?

Reply 15

OP

OK, dude im stuck not sure were to start.

density=mass/volume, ok so, i have the density

Unparseable latex formula:

2700kg m^-^3

and the volume, i think it's 12m by 0.5m do i some how put this into the equation

Unparseable latex formula:

15 x 10^-^6 m

thick.

So rework the equation to give

m = d x v

?

HELP I REALLY AM STUCK ON THIS ONE :confused:

CHEER'S
LUAP.

Reply 16

Just multiply the two length and width values by your depth. And you should get a volume it's not an equation it's just a small value of metres .000015 m. You're right about rearranging the equation as you have volume and density and what your looking for is mass. I think you can go from there yes?

Reply 17

OP

Erm, 12000 x 0.500 = 6000

Unparseable latex formula:

6000/15 x 10^-^6

=0.09

M= 2700 x 10^3/ 0.09=30000000 m^3

Sorry i know this is solid of me but have'nt really had time to scratch up,am i on the right lines? i dont think i am :confused:

i'll kick my self i know it

Reply 18