# OCR Physics Unit 2 - G482 - (June Exams Preparation)Watch

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6 years ago
#461
Has someone here posted the answers to the possible experiment questions that can come up? If so can someone refer me to it and if not can someone post them? Even one may help, I don't know any of them and this will help a great deal!!

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6 years ago
#462
Do we have to know the speed of sound in a resonance tube experiment (or checking nodes and antinodes of a microwave with a probe)?
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6 years ago
#463
(Original post by _hail)
If you think about the equation for a straight line: y= mx + c
and put the quantities in, you get: KEmax = mf + c
Then think about the equations you know involving KEmax and f (which is one according to the formula booklet I think!) this equation is hf = work function + KEmax
Rearrange: KEmax = hf - work function
also KEmax = mf + c as already found.
So h=m so h is the gradient
and c = -work function so -work function is the y intercept.
Also worth knowing that the x intercept is the threshold frequency

Yeah I thought it'd be the gradient = h, but even then the values still don't plug in correctly.

For example, when answering I used 40x10^-20 on the y axis, with 15x10^14 on the x, but according to the markscheme it should have been 6.25x10^14 instead of my value of x

I'm probably missing something stupid, but I still just don't get it
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6 years ago
#464
Standing wave experiments both wave types (longitudinal+transverse) can produce standing waves.

to set up a standing wave you can use a microwave and a metal sheet,

1) place the metal sheet some distance away from the microwave, exactly n or n.5 wavelengths away from the generator

2) microwaves will travel to the metal sheet and be reflected back upon themselves and travel in the opposite direction where they will superpose/interfere to create points of displacement equal to the amplitude [antinodes], and no displacement [nodes]. In this wave type energy is trapped in pockets and no energy is transferred, unlike a normal progressive wave.

3) measure the points of node and antinode using a microwave detector and moving it along the wave, you should detect points of zero amplitude meaning you have found a node, if you continue along it you should find a point of maximum displacement (a.k.a. amplitude), the distance between these points is (wavelength/4) from which you can determine the wavelength of the microwave.

Measuring the speed of sound using an air column.

firstly you will need a tuning fork of known frequency, then you need to determine the wavelength, before using v=fx(wavelength), to determine the wavelength you can set up a standing wave in a air colum, this consists of a column of water where you should clang the fork until you hear it resonate and add the water until you reach the fundemental frequency which is where the water cannot be any higher to produce a resonant sound, from this you can determine the wavelength as the length of the tube at this frequency is ¼(wavelength) but you need to add a constant called end correction because the node forms slightly above the water!

Youngs Double Slit

1) COHERENT light from the same source (constant phase difference)

2) 2 parallel narrow slits in an obstacle, a screen behind them

3) Light from the source passes through both slits and is diffracted

4) Interference occurs between the light from each slit at the screen

5) if waves arrive with a path difference of a multiple of whole wavelengths (n*lamda), cons interference - maxima , Arrive with a path difference of an odd multiple of half wavelengths ((n+1)/2 * lamda), destructive interference= minima

Describe an experiment to measure and obtain the Planck Constant, mentioning apparatus used and methods implemented

When an LED emits light, each electron that passes through it loses a fixed amount of energy: this energy corresponds to the energy of the emitted light. Therefore the energy lost by the electron = charge on electron x potential difference across LED. So hf=eV . The frequency of the LED light is known (manufacturers label). Setting up a circuit using an LED; a variable p.d supply is connected to the LED and increased from 0 until the LED begins to glow. The potential difference is measured for several different coloured LEDs. A graph of eV against frequency f is then plotted and the gradient of the graph is h.
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6 years ago
#465
(Original post by xomaxhox)
Yeah I thought it'd be the gradient = h, but even then the values still don't plug in correctly.

For example, when answering I used 40x10^-20 on the y axis, with 15x10^14 on the x, but according to the markscheme it should have been 6.25x10^14 instead of my value of x

I'm probably missing something stupid, but I still just don't get it
Yeah hahaha what you're doing is reading off the value of x instead of the change in x, I think it would be (15-9 or whatever it is) x 10^14 Hz
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6 years ago
#466
Do you lose marks if you add extra information? For example if it says define potential difference and you wrote ' energy transfer per unit charge from electrical to other forms' and also wrote 'measured in volts' would you lose a mark for putting measured in volts?
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6 years ago
#467
(Original post by Lucas96)
Do you lose marks if you add extra information? For example if it says define potential difference and you wrote ' energy transfer per unit charge from electrical to other forms' and also wrote 'measured in volts' would you lose a mark for putting measured in volts?
no.
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6 years ago
#468
Its not likely that the led experiment for plancs constant will come up is it? Since it came up in jan 2013
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6 years ago
#469
(Original post by _hail)
Yeah hahaha what you're doing is reading off the value of x instead of the change in x, I think it would be (15-9 or whatever it is) x 10^14 Hz

Oh wow, I knew it would be something like that haha

Appreciate the help - it's been a long exam period!
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6 years ago
#470
Do we need to know an experiment to calculate internal resistance
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6 years ago
#471
(Original post by Lucas96)
Do you lose marks if you add extra information? For example if it says define potential difference and you wrote ' energy transfer per unit charge from electrical to other forms' and also wrote 'measured in volts' would you lose a mark for putting measured in volts?
The only way you can 'lose' marks in OCR Physics is if you directly contradict your own correct statement. So if you make a point and then say the opposite, obviously you didn't know which one was correct so you wrote both hoping to get the mark for one of them, so they give you zero for that mark scheme point as you clearly didn't know the answer.
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6 years ago
#472
(Original post by xomaxhox)
Oh wow, I knew it would be something like that haha

Appreciate the help - it's been a long exam period!
No problem, at least it's nearly over! good luck for tomorrow!
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6 years ago
#473
im extremely stuck on quantum

can somene pls pls help!!!

can somebody tell me about emission spectrum, line spectrum, define spectral line, define emission and line spectrun, define band spectrum, tell me why emission and absorption spectrum are used,
describe what an absorption spectra and emission line spectra look like

what gas u need for them

i really flopped my chemistry n other exams, n neeeeeeed a really good mark in physics, n really wud appreciate help!!!

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6 years ago
#474
Panicking so much about my lack of knowledge for this paper, especially the quantum areas.
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6 years ago
#475
I think like 90% of people are going into this exam not 100% prepared. Don't worry , grade boundaries WILL be low :P
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6 years ago
#476
(Original post by scientific222)
I think like 90% of people are going into this exam not 100% prepared. Don't worry , grade boundaries WILL be low :P
LOOL i've always hated waves, its just bull.
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6 years ago
#477
(Original post by Dizzie31)
LOOL i've always hated waves, its just bull.
Its my weak area too, I can pretty much get 70-80% of the marks in electricity as a minimum. My waves is horrific. At this stage if you still don't understand the concepts I would recommend memorising the mark scheme/experiments. A lot of the marks can be picked up by simple calculations and definitions/experiments. Leaving out the "new" unknown questions would still get you an A, because you are allowed to lose around 30 marks on minimum for an A
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6 years ago
#478
(Original post by scientific222)
Its my weak area too, I can pretty much get 70-80% of the marks in electricity as a minimum. My waves is horrific. At this stage if you still don't understand the concepts I would recommend memorising the mark scheme/experiments. A lot of the marks can be picked up by simple calculations and definitions/experiments. Leaving out the "new" unknown questions would still get you an A, because you are allowed to lose around 30 marks on minimum for an A
aha i know i always get an A in mocks but i scrape the A loool
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6 years ago
#479
I still haven't learnt ANY definitions. I'm gonna go into school 2 hours before the exam tomorrow and learn as much as possible.
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6 years ago
#480
(Original post by speedstar_mm)
What do we need to know off by heart that isn't in the formula book?
Intensity: Et/A.
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