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

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I have made this thread for the June Unit 2 Physics exam for anyone interested in starting the revising process early and so that we can help eachother with what we're learning as we go. I started Unit 2 last week (an hour after my last exam, slightly brain dead).

I'm glad to hear some people thinking it would be a good idea, I haven't encountered all of this content but luckily I did a Lvl 3 VRQ in Electrical Engineering last year so hopefully I can help us quite a bit ^.^ Once I finished compiling my class notes I'll pop 'em up on this thread!

Edit: Would have finished typing up my notes tonight but got a bit distracted having my birthday, sorry will try to get everything done before the weekend's over.

I'm glad to hear some people thinking it would be a good idea, I haven't encountered all of this content but luckily I did a Lvl 3 VRQ in Electrical Engineering last year so hopefully I can help us quite a bit ^.^ Once I finished compiling my class notes I'll pop 'em up on this thread!

Edit: Would have finished typing up my notes tonight but got a bit distracted having my birthday, sorry will try to get everything done before the weekend's over.

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**PART 1/5**

Electrons drift slowly through a circuit carrying an electric current. As the electrons move they create a shift in the electrons pushing the electrons in front of them down the circuit; therefore despite the slow speed the moment an electrical circuit is switched on each of the electrical components (e.g. an LED or a resistor) receives current.

**is defined as the**

__Electric Current____flow of charge__through a conductive material. There are two types of electrical current:

**is where current is considered to be the flow of positive charge from positive (e.g. 5V) to negative (0V) due to the negative electrons traveling in the opposite direction.**

__Conventional Current__**is the movement of electrons carrying a negative charge from negative to positive.**

__Electron Flow__When there is

__no current__electrons

__move randomly__about the material causing no net drift.

When

__current__is present (despite still moving randomly) the general drift of electrons is in a specific

__direction__(towards negative).

**- Current is measured in Amperes (A) measuring the amount of electric current through a point per unit of time.**

__Amperes (Amps)__**1A=1Cs**

^{-1}**is the total amount of current that is supplied over a certain period of time. It can be defined with the following equation:**

__Electric Charge__**Q=It**(charge = current x time)

**- Charge is measured in coulombs (C) - 1C if the total charge supplied by a current of 1A in a time of 1s.**

__Coulombs__**: "The sum of the currents entering any junction is always equal to the sum of the currents leaving the junction."**

__Kirchhoff's Law__https://twitter.com/shinusuke_akki/s...263425/photo/1

Note: Charge will be conserved throughout the circuit.

**are used to measure electric current. A digital multimeter is more often used - they're a multifunctional piece of equipment that allows you to measure current, voltage and resistance. Theoretically an ammeter should have**

__Ammeters____negligible resistance__. In a circuit they need to be

__connected in series__, not in parallel, otherwise the electrical current will pass through the ammeter, limiting or stopping the current from passing through the component it is connected in parallel to (should that component present any form of resistance).

https://twitter.com/shinusuke_akki/s...592448/photo/1

**is the average velocity that an electron attains when an electric current flows. Mean drift velocity is directly proportional to current. It is given by the equation:**

__Mean Drift Velocity__**I=nAve**

Where: I = current

n = number density of electrons (electrons per unit volume)

A = cross-sectional area

v = mean drift velocity

e= electron charge (1.6x10

^{-19}C)*

*1.6x10

^{-19}C is the negative charge of an electron; this is the number you need to know - like remembering 9.81ms

^{-2}was the magnitude of acceleration due to gravity in the last unit

__Material Categories__**Conductors**contain a high number density of conducting electrons e.g. a copper wire.

**Insulators**contain very few or no conducting electrons e.g. rubber.

**Semiconductors**have properties that lie between those of conductors and insulators e.g. silicon. The conductivity of a semiconductor increases with increasing temperature, behavior opposite to that of a metal.

*THE END OF PART 1/5*
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#3

(Original post by

Electrons drift slowly through a circuit carrying an electric current. As the electrons move they create a shift in the electrons pushing the electrons in front of them down the circuit; therefore despite the slow speed the moment an electrical circuit is switched on each of the electrical components (e.g. an LED or a resistor) receives current.

When there is

When

[B]Q=It[B] (charge = current x time)

https://twitter.com/shinusuke_akki/s...263425/photo/1

https://twitter.com/shinusuke_akki/s...592448/photo/1

Where: I = current

n = number density of electrons (electrons per unit volume)

A = cross-sectional area

e= electron charge (1.6x10

*1.6x10

**Shinusuke_Akki**)**Knowledge Update 01**Electrons drift slowly through a circuit carrying an electric current. As the electrons move they create a shift in the electrons pushing the electrons in front of them down the circuit; therefore despite the slow speed the moment an electrical circuit is switched on each of the electrical components (e.g. an LED or a resistor) receives current.

**is defined as the**__Electric Current____flow of charge__through a conductive material. There are two types of electrical current:**is where current is considered to be the flow of positive charge from positive (e.g. 5V) to negative (0V) due to the negative electrons traveling in the opposite direction.**__Conventional Current__**is the movement of electrons carrying a negative charge from negative to positive.**__Electron Flow__When there is

__no current__electrons__move randomly__about the material causing no net drift.When

__current__is present (despite still moving randomly) the general drift of electrons is in a specific__direction__(towards negative).**- Current is measured in Amperes (A) measuring the amount of electric current through a point per unit of time.**__Amperes (Amps)__**1A=1Cs**^{-1}**is the total amount of current that is supplied over a certain period of time. It can be defined with the following equation:**__Electric Charge__[B]Q=It[B] (charge = current x time)

**- Charge is measured in coulombs (C) - 1C if the total charge supplied by a current of 1A in a time of 1s.**__Coulombs__**: "The sum of the currents entering any junction is always equal to the sum of the currents leaving the junction."**__Kirchhoff's Law__https://twitter.com/shinusuke_akki/s...263425/photo/1

**are used to measure electric current. A digital multimeter is more often used - they're a multifunctional piece of equipment that allows you to measure current, voltage and resistance. Theoretically an ammeter should have**__Ammeters____negligible resistance__. In a circuit they need to be__connected in series__, not in parallel, otherwise the electrical current will pass through the ammeter, limiting or stopping the current from passing through the component it is connected in parallel to (should that component present any form of resistance).https://twitter.com/shinusuke_akki/s...592448/photo/1

**is the average velocity that an electron attains when an electric current flows. Mean drift velocity is directly proportional to current. It is given by the equation:**__Mean Drift Velocity__**I=nAve**Where: I = current

n = number density of electrons (electrons per unit volume)

A = cross-sectional area

e= electron charge (1.6x10

^{-19}C)**1.6x10

^{-19}C is the negative charge of an electron; this is the number you need to know - like remembering 9.81ms^{-2}was the magnitude of acceleration due to gravity in the last unit
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(Original post by

Thanks for this, it's really helpful

**Gotzz**)Thanks for this, it's really helpful

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I'm about ready to start my write ups for part 2 of 5, I should be finishing up my topic on resistance and will write up notes and post them hopefully by this weekend if not sooner (sorry for the delay I've had some personal issues which have delayed my work temporarily but everything should be okie-dokie-lokie now) :3

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(Original post by

Why isn't there this for Unit 5 arghhhhhhhhhhhhh

**Better**)Why isn't there this for Unit 5 arghhhhhhhhhhhhh

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(Original post by

I'm really lost on emf and polarisation. Anyone care to help?

**Law-Hopeful**)I'm really lost on emf and polarisation. Anyone care to help?

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#9

I love this Unit so much it is the best! Much better than Unit 1 . I sat this exam in Jan so if anyone is unsure of anything just ask me

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#10

(Original post by

I'm really lost on emf and polarisation. Anyone care to help?

**Law-Hopeful**)I'm really lost on emf and polarisation. Anyone care to help?

There is also another equation for Emf which combines Kirchoff's Second Law have you reached to that stage yet?

For polarization what you need to know is that when light passes through a polarizing filter it will become partially polarized meaning the polarizing filter will only let through light which is acting in the same plane, all other planes of light will be blocked up.

However when you pass partially polarized light through a second polarizing filter, the intensity of light will depend on the angle the second filter is rotated. It is denoted by equation I = Io + cos^2(pheta)

Where:

- Io is the initial intensity (after passing through the first filter)

- I is the final intensity (after passing through the second filter)

- Pheta is the angle of rotation of the second filter.

Here you would note that if 2nd filter isn't rotated, such that the angle is 0 degrees light would have full intensity. Since cos 0 = 1. 1 squared = 1.

If the 2nd filter is rotated perpendicular to the first filter, such that the angle is 90 degrees no light will pass through. Since cos 90 = 0. 0 square = 0.

Also if the 2nd filter is parallel to the first filter, such that the angle is 180 degrees the light would have full intensity. Since cos 180 = -1. And -1 squared = 1.

Hope this helps

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#11

*Can anyone please help me?*

I understand the

I understand the

*currents but not the answers to the voltages.*

ANSWERS:

a) 5.0V, 0A

b)0V, 1.1mA

ANSWERS:

a) 5.0V, 0A

b)0V, 1.1mA

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#12

The resistance between PQ can be regarded as very high(infinite) when the switch S is open. So pd across PQ = 5 x infinite/(infinite + 4.7kohm) = 5V

When the switch is closed the resistance between PQ is zero. Hence pd across PQ = 5 x zero/(zero+ 4.7kohm) = 0V

When the switch is closed the resistance between PQ is zero. Hence pd across PQ = 5 x zero/(zero+ 4.7kohm) = 0V

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#13

(Original post by

The resistance between PQ can be regarded as very high(infinite) when the switch S is open. So pd across PQ = 5 x infinite/(infinite + 4.7kohm) = 5V

When the switch is closed the resistance between PQ is zero. Hence pd across PQ = 5 x zero/(zero+ 4.7kohm) = 0V

**gunner18**)The resistance between PQ can be regarded as very high(infinite) when the switch S is open. So pd across PQ = 5 x infinite/(infinite + 4.7kohm) = 5V

When the switch is closed the resistance between PQ is zero. Hence pd across PQ = 5 x zero/(zero+ 4.7kohm) = 0V

*Got it! Thanks.*

http://www.cyberphysics.co.uk/topics...sistivityQ.htm

I found this pretty useful.

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#15

I had my first physics practical before the half term, it was was the one out of 20 marks. Not sure how I did, will find out tomorrow, I think

ETA: I got 19/20! SO happy!

ETA: I got 19/20! SO happy!

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#16

(Original post by

I had my first physics practical before the half term, it was was the one out of 20 marks. Not sure how I did, will find out tomorrow, I think

**Gotzz**)I had my first physics practical before the half term, it was was the one out of 20 marks. Not sure how I did, will find out tomorrow, I think

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#18

Has anyone started doing past exam papers? How are you finding it relative to the work you were given in class? The questions considerably harder or about the same?

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#19

(Original post by

Has anyone started doing past exam papers? How are you finding it relative to the work you were given in class? The questions considerably harder or about the same?

**brawlerpit**)Has anyone started doing past exam papers? How are you finding it relative to the work you were given in class? The questions considerably harder or about the same?

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#20

(Original post by

Can't start doing exam papers as we've nowhere near covered all the content yet. Nerve-racking, really.

**Dusky Mauve**)Can't start doing exam papers as we've nowhere near covered all the content yet. Nerve-racking, really.

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