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electricity question

MS
http://www.scribd.com/mobile/doc/46124583?width=768
QP
http://www.scribd.com/mobile/doc/50654250?width=768

I need help on question 18.

With the first part why do you need a variable power supply/variable resistor?

In cii why can't you say
In I=nAvq the n value increases as there are more free electrons per metre cubed
With I, A and q constant, drift velocity decreases??
How do I know whether I am supposed to say this or say that there are more atomic vibrations, ausing more collisions between atoms and electrons, so resistance increases while drift velocity decreases?

Thanks
(edited 11 years ago)
Reply 1
Avatar for joostan
joostan
13
Original post by krisshP
MS
http://www.scribd.com/mobile/doc/46124583?width=768
QP
http://www.scribd.com/mobile/doc/50654250?width=768

I need help on question 18.

With the first part why do you need a variable power supply/variable resistor?

In cii why can't you say
In I=nAvq the n value increases as there are more free electrons per metre cubed
With I, A and q constant, drift velocity decreases??
How do I know whether I am supposed to say this or say that there are more atomic vibrations, ausing more collisions between atoms and electrons, so resistance increases while drift velocity decreases?

Thanks


n will only increase if this is a thermistor - which it is not. The number of electrons free in the wire remains constant.
You will need to know the bold in general, but what you said for a thermistor.
Reply 2
Avatar for krisshP
krisshP
OP
14
Original post by joostan
n will only increase if this is a thermistor - which it is not. The number of electrons free in the wire remains constant.
You will need to know the bold in general, but what you said for a thermistor.


THANKS!:smile:
Reply 3
Avatar for joostan
joostan
13
Original post by krisshP
THANKS!:smile:


Anytime :smile:
Reply 4
Avatar for krisshP
krisshP
OP
14
Original post by joostan
Anytime :smile:


Any ideas about why you need a variable power supply/variable resistor for the first part in the same question?
Reply 5
Avatar for joostan
joostan
13
Original post by krisshP
Any ideas about why you need a variable power supply/variable resistor for the first part in the same question?


The mark scheme doesn't state that it MUST be a variable power supply/resistor. . .

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