OCR Physics A G482, Electrons, Waves and Photons, 25th May 2012

Scroll to see replies

Reply 20

jndk109

Original post by Wilko94

Does anyone have the Jan 11 paper and mark scheme?

here ya go buddy hope it helps:

(edited 12 years ago)

G482 2011 Jan MS.pdf251.5KB

G482 2011 Jan.pdf279.0KB

Reply 21

frizz101

Original post by xoxfazjazxox

Hello everyone :biggrin:

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

I don't know if this helps, but when I'm presented with a question like that I look at the units. For current, we need the units as Amps which is Coulombs/second.

So, the charge is 6.4Cm^-2, multiply that by the width which is 0.04 m, and we get 0.256 Cm^-1. Then, if we multiply this by the speed, 0.8ms^-1, we get 0.2048Cs^-1 because C/m multiplied by m/s gives C/s.

when rounded it gives 0.2 which is your answer, and I hope it's right, but I'm not sure really.

didnt notice the "mu" post you made so please take that into consideration cos I'm probs wrong

(edited 12 years ago)

Reply 22

Summerdays

The Van de Graff sweeps an area of 0.032m^2 a second.

We know that current is the rate of flow of charge, i.e: Charge/second.

Charge per metre squared x Area sweeped per second gives charge per second = current

So, 0.032m^2s^-1 x 6.4Cm^-2 = 0.2048.

Reply 23

Summerdays

Original post by Jukeboxing

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

I got the same answer.

Reply 24

shyro1000

Original post by wibletg

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.

thats cleared things up bud thanks alot :smile:

Reply 25

CharleyChester

Basically I hate Quantum.

Reply 26

xoxfazjazxox

Original post by Summerdays

THANK YOUUU, this seems right!

Reply 27

xoxfazjazxox

Original post by Jukeboxing

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

Haha, thanks! It seems so easy now. I just really hate it when the questions are waffely! I AM SOOOO SCARED ABOUT MONDAY.
THANKSSSSS.

Reply 28

donzy

electricity is pretty straightforward
waves is okay, a bit annoying
quantum phenomena.... i dont even wanna go there :afraid:

Reply 29

CharleyChester

Can someone give me a brief summary of what we actually need to know for the Quantum section. It seems to me i know everything for Electricity and Waves, but I can't recall anything from Quantum D:

Reply 30

sweetascandy

Ughhh I'm really dreading this exam. I HATE waves with a passion. How are you guys revising? I'm going through the spec (it's available on the OCR website if anyone wants it!) and I'm just making cue cards, so I am pretty much basing my revision on the spec. :smile:

Reply 31

Jukeboxing

Original post by sweetascandy

Its good that your using the spec, but that just doesnt cut it sometimes. They will always ask you questions that arent in the specification, to seperate the A grade students.

Use the textbook, i know most of the stuff looks like its unnecessary but you'd be suprised when they ask about it the exam.

Reply 32

sweetascandy

Original post by Jukeboxing

Well yeah I guess, but the thing is, there's just Sooo much in the textbook and I hate revising from the textbook! And to make it even worse, we don't even have the whole set of class notes. I'm just gunna try and do a hell of a lot of past papers after I finish revising the syllabus, which will (hopefully) enhance my learning. Thanks for the advice though. :smile:

Reply 33

Pheylan

Original post by sweetascandy

I HATE waves with a passion.

This. Electricity and quantum seem to be alright but I just want waves to go and die

Reply 34

shyro1000

really struggling to get the whole photon experiment and how to work out energy levels, help? :frown:

Reply 35

sweetascandy

Original post by Pheylan

This. Electricity and quantum seem to be alright but I just want waves to go and die

I feel the same way! It's actually ridiculous how we have to know all the different wavelengths for each of the EM spectrum. Bur srsly though, after this exam, no more physics for me.

Reply 36

Michael_4180

I somehow managed to get 150/150 for this exam in january. My advice for everyone taking it is to memorise the definitions directly quoted on the specification, do as many book questions as possible, and to make sure you understand proportionality e.g. if intensity is multiplied by 1.5 what happens to amplitude?. Lastly, other revision books should be avoided, and for memorising the experiments try to find past mark scheme answers on such questions and memorise those- it will save you time.

Reply 37

Jukeboxing

I suspect these will be asked:

Electricity

Describe the uses and benefits of using light-emitting diodes.

Describe an experiment to obtain the I-V characteristics of a resistor at constant temperature, filament lamp and light emitting diode.

Define the Coulomb

Explain that electric current is a net flow of charged particles

Describe the difference betwen conductors, semiconductors and insulators in terms of the number density n.

Explain the meaning of the term Terminal P.d.

Waves

Explain what is meant by reflection and refraction.

State typical values for the wavelengths of the different regions of the EM spectrum.

Describe some practical uses of EM waves.

Recall and use Malus law

State principle of superposition

Apply graphical methods to illustrate the principle of superposition

Describe Experiments that demonstrate two-source interference using sound, light and microwaves.

Describe Young double slit experiment.

Describe experiment to determine wavelenght of monochromatic light.

Describe similarities and differences between progressive and stationary waves.

Define and use the terms the fundamental mode of vibration and harmonics

Determine the speed of sound in air from measurements on stationary waves in a pipe closed at one end.

Quantum

Define and use the terms work function and threshold frequency.

Use einsteins equation hf = work function + KEmax

Explain that diffractions of elctrons by matter can be used to determine arrangements of atoms and size of nuclei

Describe origin of emission and absoption line spectra

Describe and experiment using LEDs to estimate plancks constant

Let me know if anythings been asked already or if i'm missing something.