[Joseppea]

So, I was thinking it'd be a good idea for people sitting this exam (or a similar one if it's applicable) to ask/answer questions.

Here's how it works:

I will ask a question, someone will hopefully answer it and then ask another question! Then anyone can join in and it'll hopefully be useful for everyone

Here goes:

What are the 4 properties of waves and which 2 are exclusive to waves?

[ebmaj7]

Reflection, Refraction, Superposition and... Diffraction?

Explain the meanings of interference and coherence?

[shuty]

Heyy, have you guys started revising yet? and how do you revise? any help? thanks...

[Jukeboxing]

Yh I got this exam aswell. I'm also retaking mechanis, I got a C. Im taking a different approach to my revision this time by using the specification and make sure I know everything from it.

[taunt]

yep got this exam cumin up....scared as hell coz i cant seem to revise properly

well i dont get all this resistance and emf business

[shyro1000]

correct me if im wrong but i think interferance is what affects waves when two or more waves collide. it comes in two forms constructive and destructive. coherance is when waves have the same qualities, such as wavelength and such

[=coldfire=]

Just if it helps anyone on here. I made an annotated formula sheet for this unit, which I, and those in my class have found very useful. It is great to help during revision, and then you should become familiar with all of the information on it, and only need to to occassionaly check things. It has all the equations, all the symbols used, and what they mean, (e.g. n=number of charge carries per meter cubed), and simple names for them which give their use. I hope it is able to help some of you, it has kindly been uploaded here:

http://core.physicsinfo.co.uk/download.php?file=1326

Preview

[Joseppea]

We just started the quantum mechanics bit... O_O

This is fun

[DeeGrade]

Hoping to get full UMS again then i'd have full UMS at as


-Cambridge Engineering 2012 (is the goal)-

[taunt]

(Original post by DeeGrade)
Hoping to get full UMS again then i'd have full UMS at as


-Cambridge Engineering 2012 (is the goal)-

well arent u a lucky *****

btw thats a compliment lol

[Ralphus J]

Anyone got a list for the circuit symbols you need to know?

[Jukeboxing]

(Original post by Ralphus J)
Anyone got a list for the circuit symbols you need to know?

[Ralphus J]

^
Cheers lad

[Wilko94]

Does anyone have the Jan 11 paper and mark scheme?

[Pneus]

Make sure you revise intensity, as you need to know what it is proportional too; without it being available to you in the forumla booklet.

I (prop.) a^2

(Original post by Wilko94)
Does anyone have the Jan 11 paper and mark scheme?

I have a hard copy of the paper, however no mark scheme.

[shyro1000]

can anyone help me understand de broglie wavelength as i had an exam when it was covered and never learnt it

[xoxfazjazxox]

Hello everyone

I am having a little bit of trouble with these questions from the textbook and i was wondering whether anyone would be as kind as to explain them to me!

1) A diode usually has a very low resistance when connected in a circuit in a direction that passes a current. To limit the current in the circuit, the usual procedure is to add a safety resistor in series with the diode. When a 220 ohm resistor is connected in series with an LED to a 4.5V supply, the current in the circuit is 10mA. Calculate the p.d. across the resistor and hence the resistance of the LED.

2) The belt of a school Van de Graaff generator is 40mm wide. It travels at a speed of 0.8m/s. Charge is sprayed onto the belt at 6.4?Cm^-2. Calculate the current, in ?A, carried to the sphere by the belt.

I KNOW THAT THE ANSWER FOR q2 IS 0.2, BUT I DO NOT KNOW HOW?!

Many Thanks

[xoxfazjazxox]

The question mark before A is supposed to represent micro, as in mu. ^^^

[wibletg]

(Original post by shyro1000)
can anyone help me understand de broglie wavelength as i had an exam when it was covered and never learnt it

basically mate

it's a way of working out if an object is going to show wave properties such as reflection, diffraction etc.

de broglie wavelength = h (plancks constant) / mv

where mv = mass x velocity of object (i.e. its momentum)

so the wavelength is inversely proportional to an objects momentum. if the momentum increases the wavelength decreases.

in the case of electron diffraction, if the wavelength is small enough after the electrons have been accelerated using an 'electron gun' then the electrons are going to fit through the graphite at the other end of the diffraction tube and thus form 'rings', because the graphite acts as a 'slitt.

[Jukeboxing]

(Original post by xoxfazjazxox)
Hello everyone

I am having a little bit of trouble with these questions from the textbook and i was wondering whether anyone would be as kind as to explain them to me!

1) A diode usually has a very low resistance when connected in a circuit in a direction that passes a current. To limit the current in the circuit, the usual procedure is to add a safety resistor in series with the diode. When a 220 ohm resistor is connected in series with an LED to a 4.5V supply, the current in the circuit is 10mA. Calculate the p.d. across the resistor and hence the resistance of the LED.

2) The belt of a school Van de Graaff generator is 40mm wide. It travels at a speed of 0.8m/s. Charge is sprayed onto the belt at 6.4?Cm^-2. Calculate the current, in ?A, carried to the sphere by the belt.

I KNOW THAT THE ANSWER FOR q2 IS 0.2, BUT I DO NOT KNOW HOW?!

Many Thanks

1) p.d across resistor -
V=IR, (10x10^-3)x 220 = 2.2V

Resistance of the LED -
R=V/I 4.5-2.2 = 2.3V 2.3/10x10^-3 = 230 ohms

Check if thats correct.

Still looking at Q2