# AS Physics OCR: Electric Current

Stuck on this question, cannot understand how they got this answer:

A car battery is labelled '50Ah'. This means that it can supply a current of 50A for one hour.
a) For how long could the battery supply a continuous current of 200A needed to start the car?
b) Calculate the charge which flows past a point in the circuit in this time

Have to use the equation: Charge= Current x Time

I got a) 4 hours and b) 2.88x10^6 C
However, the answer is a) 0.25h and b) 1.8x10^5 C
Amp hours is a measure of the capacity of the battery. It's amps multiplied by hours.
If the current (amps) goes up then the hours (time) must go down because the capacity of the battery is fixed.
Original post by theconsciousindian
Stuck on this question, cannot understand how they got this answer:

A car battery is labelled '50Ah'. This means that it can supply a current of 50A for one hour.
a) For how long could the battery supply a continuous current of 200A needed to start the car?
b) Calculate the charge which flows past a point in the circuit in this time

Have to use the equation: Charge= Current x Time

I got a) 4 hours and b) 2.88x10^6 C
However, the answer is a) 0.25h and b) 1.8x10^5 C

If it can supply 50A for 1 hour then it could supply
100A for half an hour
or 25A for 2 hours
The product Amps x time must be the same.
50 x 1 = 100 x 1/2 = 25 x 2 etc
So it can supply 200A for ...

You should get part two right with the correct value for time.
Hi five for picking physics I bloody regret it!!!!!!!!
Original post by Nav_Mallhi
Hi five for picking physics I bloody regret it!!!!!!!!

#HI5

i have a mini physics test tomorrow and im quite scared tbh
where are you from nav?
Original post by theconsciousindian
#HI5

i have a mini physics test tomorrow and im quite scared tbh
where are you from nav?

Don't worry about it, you'll be fine and plus it's only a small test not the real thing....... this is how I reassure myself lol.... Did it work on you?
I'm from Wolverhampton, what about you?
Your already on that were still doing the other unit
Original post by Nav_Mallhi
Don't worry about it, you'll be fine and plus it's only a small test not the real thing....... this is how I reassure myself lol.... Did it work on you?
I'm from Wolverhampton, what about you?

yeah i know but i have a real bitch of a teacher. & did what work on me?

& really, i know a nav from wolverhampton - what year you in?
Original post by Future Drugist
Your already on that were still doing the other unit

i think you might have started a different unit first cause this was the first unit we did for electricity.
Original post by theconsciousindian
yeah i know but i have a real bitch of a teacher. & did what work on me?

& really, i know a nav from wolverhampton - what year you in?

You are not the only one with a crap teacher, my teacher is evil, I wanted to stab her with my blunt pencil the other day, no joke
I just wanted to know if the reassurance worked on you- forget it if you don't get it.
You do probably know a lot a Nav's but I'm not one of them btw I do know a lot of consciousindians though. I'm in year 12 what about you?
(edited 11 years ago)
Original post by pororohhbji
Hello, could u please explain why the answer of is 1.8 x 10^5 C?? I followed the formula which is charge = current x time and which I wrote 200A x 15s = 3000?? And so my answer for b is 3000 C....

The thread is 9 years old, it's probably best to make new one when you want a question answered.

the amount of time you have multiplied by is incorrect, remember the original question gives time in hours.