# Electricity physics questions a level

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#1
Hi I was just wondering if someone could help me out with some doubts that I had, thank you in advance
sorry some of my questions might sound stupid lol but i rly like to understand stuff well.
1. if you think about it, why is R= V/I? the equation is essentially saying that the resistance is the potential difference per unit of current??:/
2. in my CGP book there's a section abt ideal voltmeters and ammeters, and they've described an ideal voltmeter as something that has infinite resistance and an ideal ammeter is something that has no resistance. but why do those two things make them ideal? please could someone explain this a bit xxx
3. also im a bit confused about the diff btwn resistivity and resistance. apparently, p is the property of a material, whereas the resistance is a property of an object of the material and dimensions of the object. but what does that even mean

thank you
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8 months ago
#2
Yeah potential difference per unit of current is a good way of thinking about resistance IMO.
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This is about minimising the effect the measuring device on the quantity you're trying to measure

Ammeters are used by placing them in series at a point in the circuit where you want to measure the current flowing - but inserting a high resistance reduces the current flowing. zero resistance is ideal because it has no effect on the current flowing through it.

Voltmeters are used in parallel where you're interested in the PD between 2 points - but connecting a low resistance between two points reduces the effective resistance between those points (resistors in parallel rule) and effects the PD between them. infinite resistance is ideal because infinite resistance in parallel has zero effect on the effective resistance..
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Are you ok with some materials being better electrical conductors than others? if you wanted to make resistors with the same resistance out of wires that were the same diameter the resistor made out of a good conductor like copper would have to use a longer length of wire than a resistor the same value made out of a less good conductor like iron.

if you say something is a good conductor you're saying it has a high conductivity
resistivity is just 1/conductivity
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8 months ago
#3
Moooood 😭 I made it out of AS physics but now A2 is making me suffer
1
#4
haha nws lol
wait do u study physics at uni? wdut of it?? im rly struggling to decide btwn physics and engineering
(Original post by Joinedup)
Yeah potential difference per unit of current is a good way of thinking about resistance IMO.
---
This is about minimising the effect the measuring device on the quantity you're trying to measure

Ammeters are used by placing them in series at a point in the circuit where you want to measure the current flowing - but inserting a high resistance reduces the current flowing. zero resistance is ideal because it has no effect on the current flowing through it.

Voltmeters are used in parallel where you're interested in the PD between 2 points - but connecting a low resistance between two points reduces the effective resistance between those points (resistors in parallel rule) and effects the PD between them. infinite resistance is ideal because infinite resistance in parallel has zero effect on the effective resistance..
---
Are you ok with some materials being better electrical conductors than others? if you wanted to make resistors with the same resistance out of wires that were the same diameter the resistor made out of a good conductor like copper would have to use a longer length of wire than a resistor the same value made out of a less good conductor like iron.

if you say something is a good conductor you're saying it has a high conductivity
resistivity is just 1/conductivity
thank you soo much makes wayy more sense now x
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#5
Aha same in in yr 12 too...just watch loads of videos and make good notes and you'll see your grades improve xx that's what I do anyways lol
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#6
wdum by the last bit?put in ur place?
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#7
):
I'm sure you're not that bad... If you ever need help I can try
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