You are Here: Home >< A-levels

# A2 Physics A Paper A- HELP PLEASE!!!! watch

1. HELP!!!! I need urgent help.
Two issues:
One, when they ask for the initial number of nuclei, and you have worked out the decay constant, λ, already, you use the formula:

delta N/delta t = -λN

but in all the exam questions, when that comes up, they just use the initial activity for (delta N/delta t). Isn't that wrong? Cuz i usually use N at a single half life, so N is half of the original activity, and t is a half life. But thats wrong. WHHY?????????????????????

Two, does anyone know what questions came up on Paper A of Jan 05, cuz I was not in school for the mocks, and my class mates are all stupid, lol.

2. U know the equation N/N0=E^-lambda t? Well the N.No is the half life when you remove the base e so ln2=lambda T, and that T I think is is the time taken for half(ln2) to have disintergrated), so lets say they give you the rate of decay, ie lambda, to find time, u divide ln2 by lambda to get time taken, i still havent found any past paers asking for the half life!!! If i aint helped, go to and look at the stuff they've got.
http://hyperphysics.phy-astr.gsu.edu...halfli.html#c1
3. The two equations I would use, as said above would be:

I personally, doing A2 Salters Horners, have never seen a question asking for the half life, they all seem to ask the fraction left after a certain time or the nuclei left after a certain time.

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.

This forum is supported by:
Updated: June 14, 2005
Today on TSR

### IT'S TODAY!

A-level results chat here

Poll

## All the essentials

### Student life: what to expect

What it's really like going to uni

### Essay expert

Learn to write like a pro with our ultimate essay guide.

### Create a study plan

Get your head around what you need to do and when with the study planner tool.

### Resources by subject

Everything from mind maps to class notes.

### Study tips from A* students

Students who got top grades in their A-levels share their secrets