Yes it was a curve.The value of resistance that corresponds to 0.25 Wm^-2 was 0.5 kilo ohm= 500 ohm

you use the equation
0.6= 6 x 500 / 500 + R
R=4500 ohm

(edited 8 years ago)

Reply 46

hiddensecrets

I dont remember , do you remember the value? It was the resistance x (width x thickness) / length
I guess... :/

Original post by Dr.strange12

anyways the resistivity of the metal was 6.5* 10^-7

Reply 47

Dr.strange12

ah dang i thought that was resistance of just LDR dang. oh well i think i lost 10 marks max its an A good enough considering i had no teacher to teach me the course

Reply 48

hiddensecrets

Don't worry you'll do great, a large number of students messed up many of the calculations..hope that would bring the grade boundaries lower
I guess an A will be 55ish :/
So you still have a great chance of getting an A! :biggrin:

Original post by Dr.strange12

ah dang i thought that was resistance of just LDR dang. oh well i think i lost 10 marks max its an A good enough considering i had no teacher to teach me the course

Reply 49

Dr.strange12

yay now i have three months of summer. time to chill

Reply 50

examgirl414

Guys what about the reflector detector questions

Reply 51

AvWOW

Original post by C369

I got 3.3*10^-9
I used s=2d/t
Sub 0.5 for d and c for s
How did u do it???
What was the answer for mcq about resistance????
Was it b

I used the same t= 2d/t
but I used 1km... 1000m. I thought highest distance gives largest pulse duration.
mcq I think was B... or was it C?
It was R+ (1/ 1/R+1/R)

Reply 52

AvWOW

Original post by examgirl414

i got 4.5 kilo ohms, thats okay yeah?

haha of course. Same thing! :P

Reply 53

AvWOW

[QUOTE="mdfaiz99;56586429"]

Original post by hiddensecrets

The diamond question you use refractive index equation
For glass-
1/1.5=Sin28/Sinr
r=44.8 degrees

For diamond
1/2.42=sin28/sinr
r=math error
which means there is no refractive angle
The angle is reflected back into the diamond( total internal reflection)

Why is it 1/refractive index? I Just did refractive index=sin i/sin r and got 18 degrees and I was like how the hell does it move towards the normal ??? :frown:

ooh I messed up

I got 18 for diamond and 11 for glass :/
And why did you use 28? the angle that was given was with the normal right? Ithink it was 35 degrees?

Reply 54

mdfaiz99

Original post by hiddensecrets

The diamond question you use refractive index equation
For glass-
1/1.5=Sin28/Sinr
r=44.8 degrees

For diamond
1/2.42=sin28/sinr
r=math error
which means there is no refractive angle
The angle is reflected back into the diamond( total internal reflection)

For the LDR question I got 4500 ohms= 4.5 Kilo Ohms

Why is it 1/refractive index? I Just did refractive index=sin i/sin r and got 18 degrees and I was like how the hell does it move towards the normal ??? :frown:

ooh I messed up

Reply 55

AvWOW

Original post by hiddensecrets

How on earth will an angle move towards the normal when passing from glass to air.It has to move away since air is a rarer medium xD
dont worry you are right..i Mean this answer makes sense,the 18 degree answer doesnt :P

Pretty sure it was moving form air to glass....
I got 18 for diamond and 11 for glass. Looked right to me....
besides... you have to draw the angle in the given diagram. And If you say it undergoes TIR you can't say by which angle so you can't draw it!

Reply 56

MadZler

haha me trying to figure our why im getting 0.24... on a show that the wavelength is about 2cm... realizing im in meters :P

Reply 57

iKaneee

I dont know why but for some stupid reason on question 11 i couldn't show that for
I=nAvq, that they both equated to the Ampere, I'm so pissed off considering i take maths lmao

Reply 58

MadZler

Original post by iKaneee

I dont know why but for some stupid reason on question 11 i couldn't show that for
I=nAvq, that they both equated to the Ampere, I'm so pissed off considering i take maths lmao

basically n is in m^-3, q is in c, v is in ms^-1 and A is in m^2. the meters cancel and you get coulomb per second, which is an amp.

only 3 marks no worries

Reply 59

iKaneee

Original post by MadZler

basically n is in m^-3, q is in c, v is in ms^-1 and A is in m^2. the meters cancel and you get coulomb per second, which is an amp.

only 3 marks no worries

Ohhh damn I forgot n was m^-3 .. oh well.. Did you think the paper was hard? I thought it was okay, but I could see alot of people struggling for time due to there being 21 questions!