AQA AS Physics A Unit 1 January 2012 Discussion

Yes , also this decay is a weak interaction so strangeness doesn't have to be conserved. Unlike the original interaction which was a strong interaction.

It took me a while to figure why i was getting those questions wrong, quite easy now.

I am still not shure how you figure out if a reaction is due to the strong interaction, is it if there are no quark changes?

Correct me if I'm wrong, but doesn't the question itself make it clear that it's the strong force?

A weak interaction can be defined as an interaction that involves a change of quark flavour

A weak interaction can be defined as an interaction that involves a change of quark flavour

Thanks. But what do you mean by "quark flavour"?

I don't understand how you can tell if a reaction is strong force or weak force. Please help?

Does anyone enjoy the Aqa physics textbook. I find it dull- using cgp instead

I've been using AQA and yep, I find it really dull, as soon as I get onto the photoelectric effect, my mind just goes blank. Is CGP any good? :/

Didn't know that the weak reactions were caused by change in quark flavour - that's quite interesting.

CGP's mostly good for the questions if you don't know how to do a topic, since the questions lay out the method for you. Personally, I can't recommend making your own notes enough - you know what you'l remember the best, so you can tailor your guide to what works for you.

Not needing to look in a book means that you can even plaster your walls in notes if you want to. I already have, myself...

Also, can someone explain the Photoelectric effect? and answer this

'The photoelectric effect suggests that electromagnetic waves can exhibit particle - like behaviour. Explain what is meant by threshold frequency and why the existence of a threshold frequency supports the particle nature of electromagnetic waves.'

will be much appreciated.

I don't think the text book goes into enough detail does anybody have any notes or on line revision website they use , It would be really helpful

Electrons can be emitted from a metal surface if given energy greater than or equal to the work function of the metal ( h * f(threshold) ). This energy can be supplied by incident light photons of energy h * f(threshold) or greater - the threshold frequency therefore being the minimum frequency that the incident light must have in order to liberate electrons. This is shown to be the case as if f < f(threshold), no electrons are emitted, regardless of the intensity of the incident light. The light must therefore act as particles (photons) whose energy = h * f. Increasing the intensity if f is greater than or equal to f(threshold) will increase the rate of emission of electrons, indicating that the number of incident photons per second has increased. Each electron can absorb only one photon.

I think that that just about answers it, but if anyone can think of anything else to add, feel free to!

edit. I didn't realise that you wanted the photoelectric effect explained in and of itself as well sorry. I think the following covers it, but am happy to take suggestions and/or clarify anything!

The photoelectric effect is the emission of electrons from a metal surface due to incident photons of energy (h * f) greater than or equal to the work function (h * f(threshold)) of the metal, the minimum energy required to liberate an electron. Each electron can absorb only one photon. Emitted electrons have maximum kinetic energy equal to the difference between the photon energy and work function, and this varies up to a maximum due to electrons below the surface having to do work to get to the surface before being emitted. The photoelectric effect provides evidence for the particle nature of light, as if light were acting as waves, energy could be absorbed by the electrons over a period of time until reaching the required amount and being emitted. This is not the case - electrons are emitted immediately once f is greater than or equal to the threshold frequency. Furthermore, if light were acting as waves, the energy transferred by the light would be dependant on its intensity. This is not the case - if f < f(threshold), then increasing the intensity will have no effect; and if f is greater than or equal to f(threshold), then increasing the intensity will increase the rate of emission of electrons, indicating that there are more photons landing on the metal surface per second.