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

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I wrote that it decreased because the potential difference across the LDR decreased, and they're both parallel, so..
But that might be completely wrong. Ugh.

Yes I put the same as this, due to the ratio of the potential divider decreasing...

Reply 761

JAY21564

Original post by Kamal_Voltaic

I wrote that it decreased because the potential difference across the LDR decreased, and they're both parallel, so..
But that might be completely wrong. Ugh.

I wrote that the PD will decrease too, but because current is able to flow through the LDR and as an alternative route, as the resistance of the LDR was 400 but the other resister was 750 :smile:

Posted from TSR Mobile

Reply 762

Gotzz

Original post by ellsss

what did people write about for how the potential difference changes in the resistor as the LDR's resistance decreases?

Something like:
Current through LDR increases
Current in circuit increases
P.d. across LDR increases
LDR in parallel with resistor so p.d. of LDR increases.
Or something like that :confused:

Reply 763

bradley-tracey

Original post by Gotzz

I wrote: a wave that transfers energy from one point to another.
But I know that's not enough for 2 marks :/

yeah i think you gain the second mark for saying that they move energy in the form of vibrations/ oscillations of the particles.

Reply 764

Gotzz

Original post by Dr.Monstaa

. No, I didn't do that, I rearranged lambda=ax/D. To get x and used the values provided

The 8mm value provided didn't give the value of x because it wasn't the spacing between two bright fringes, it was for like 4 bright fringes

Reply 765

Mule

Original post by JAY21564

I wrote that the PD will decrease too, but because current is able to flow through the LDR and as an alternative route, as the resistance of the LDR was 400 but the other resister was 750 :smile:

Posted from TSR Mobile

I got that as the resistance of the LDR decreases the total resistance of the circuit increases, so the total current in the circuit must increase. For the fixed resistor, it would have a greater voltage then, and as voltage is shared the voltage across the LDR must be less.

For that charged battery one though, ended up with 7.11 :frown:

I think I did E=VIt or something

Reply 766

Georgehigginson

Original post by ellsss

what did people write about for how the potential difference changes in the resistor as the LDR's resistance decreases?

I put that more current could flow through the LDR so the potential difference of the LDR increases, less current will therefore go through the fixed resistor so as V=IR the potential difference of the fixed resistor will decrease

Reply 767

hannahsm

For the first semiconductor/resistivity question did you guys say that resisitivity increased with temperature due to more electrons breaking free from their atoms. So the current increasing and the resistance decreasing.

EDIT: i meant to say resistivity decreased sox

(edited 10 years ago)

Reply 768

zcanf

Anyone onto an unoffical markscheme?

Reply 769

MelissaW_xo

Original post by hannahsm

I think resistivity decreases with temperature (aswell as resistance)

Reply 770

cuckoo99

Original post by J10

What do people think gradeboundaries willl be for an A (and for 130, 140 and 150 UMS)?

for an A it will prob be like 65 or so

Reply 771

Gotzz

Original post by hannahsm

No, I kinda just talked about the gradient getting steeper as the p.d. increases and R=1/gradient so resistance decreases, so resistivity decreases as they're proportional.
ETA: oh and I said as current increases, temperature increases.

Reply 772

bradley-tracey

Original post by Gotzz

Something like:
Current through LDR increases
Current in circuit increases
P.d. across LDR increases
LDR in parallel with resistor so p.d. of LDR increases.
Or something like that :confused:

with a mention of the fixed resistor and LDR in parallel shows that the voltage over both of them is equal so i think you would treat it as adding resistors in parallel so the overall resistance of both of them together resulted in a lower resistance so the P.d share would fall in favour on the other fixed resistor (R1 i think they called it) causing there to be a decrease in voltage across the LDR and fixed resistor that i was in parallel with. i think.

Reply 773

hannahsm

Original post by MelissaW_xo

I think resistivity decreases with temperature (aswell as resistance)

so soz thats what i meant...

Reply 774

AhmadB

Original post by Gotzz

How many s.f. was your charge to?

I don't remember what i used for charge :frown:

Reply 775

J10

I put that, for semiconductors, temperature is proportonal to the inverse of resistance, which implies that as temperature increases, resistance will decrease, which then tells us that as temperature increases, the resistivity will also decrease. And then some other stuff to prove that