Edexcel PHYSICS Doubts

[narnia]

http://www.xtremepapers.me/Edexcel/Advanced%20Level/Physics/2006%20Jan/6731_01_que_20060117.pdf

question 2 b (i)
how do we know that we have to subtract 40 from 220 while calculating anti-clockwise moments??
i was just goin the normal way : 220*10^-3 W=228 *10^-3 (9)
but the answer does not end up to 11 N?!


please explain asap!
thanks!

[The Golden Girl =D]

could you plz tell me the safety precautions for any experiment in physics.

Thx in advance

[Malak]

A ray of light travelling in air, strikes the middle of one face of an equilateral glass prism.

State what happens to the following properties as the light goes from the air into the glass.
Frequency
Wavelength
Speed

The ms says that wavelength will decrease while the frequency stays the same..Confused at this part, y would the wavelength change?
I know the speed increases.

Thanks

[Hanooush]

could you plz tell me the safety precautions for any experiment in physics.

Thx in advance

well, there arent plenty of safety precautions. however, these are the ones that I know.

for experiments that invlove hanging masses e.g. testing the relationship between force and acceleration OR acceleration due to gravity experiments.
You would place a piece of sponge beneath the hanging masses to avoid any injury and to reduce their impact on the ground.

If you are to measure the mass of heavy objects, measure them using scales placed on the floor.

[Hanooush]

If an experiment involved using light gates/trolley
Make sure that the trolley and light gates are positioned away from the edge so that the trolley will stop on the bench (that one doesnt make too much sense to me, I copied it off a book).

Force-extention experiments:
Wear safety goggles in case of the wire breaks. Also sponge/soft material is placed beneath the masses.

Polarised light exp.:
Do not look directly into the beam and wear eye protection =/

That's it ,, there may be a couple more but it depends on the experiment given

[Hanooush]

The ms says that wavelength will decrease while the frequency stays the same..Confused at this part, y would the wavelength change?
I know the speed increases.

First of all, the speed doesn't increase. it DECREASES. This is because light has moved from a less dense medium (air) to more dense one (glass). The denser the object, the harder something can pass through, that's why the speed decreases and so the wavelength decreases as well.
The reason why the wavelength decreases can be explained using the equation:
speed=wavelength x frequency. Frequency remains the same and we know that speed decreases, so wavelength must decrease as well.

[Hanooush]

Could someone please explain me the graph of current against voltage (I against V) for a semiconductor diode? Why does it behave that way? Current starts off at 0 for some time, then it increases.

Here's a link to a website which includes an image of the graph.
http://www.pfk.ff.vu.lt/lectures/funkc_dariniai/diod/p-n_devices.htm

Thanks in advance
 

[The Golden Girl =D]

Could someone please explain me the graph of current against voltage (I against V) for a semiconductor diode? Why does it behave that way? Current starts off at 0 for some time, then it increases.

Here's a link to a website which includes an image of the graph.
http://www.pfk.ff.vu.lt/lectures/funkc_dariniai/diod/p-n_devices.htm

Thanks in advance
 

Well it's because the semiconductor diode doesn't work unless it's 0.6v if  it's made of Silicon and it won't work if it's made from germanium unless it's 0.4 v

[The Golden Girl =D]

If an experiment involved using light gates/trolley
Make sure that the trolley and light gates are positioned away from the edge so that the trolley will stop on the bench (that one doesnt make too much sense to me, I copied it off a book).

Force-extention experiments:
Wear safety goggles in case of the wire breaks. Also sponge/soft material is placed beneath the masses.

Polarised light exp.:
Do not look directly into the beam and wear eye protection =/

That's it ,, there may be a couple more but it depends on the experiment given

Thanks a lot mate , if you know more plz do let me know.

I have one though , wear goggles if you're working with wires cuz it might snap.

[red_911]

if an equation is given : s=ut+0.5at^2
and we plot a graph of Distance/time with time .. how can we prove that the graph will be a straight line ? 
it is question 9 C of physics specimen paper

http://www.xtremepapers.me/Edexcel/Advanced%20Level/Physics/Specimen/Physics-Practical-Alternative-SAMs.pdf

[Malak]

Q:
Scientists have discovered recently that the dung beetle can navigate using polarised moonlight. The beetles hunt for fresh dung. When they find some each beetle makes a small ball. To keep this ball for itself it needs to remove it quickly. The beetle pushes the ball along with its back legs while moving with its front legs and keeping its head down. Using the plane of the polarised moonlight as a guide lets the beetle run away in a straight line.
The beetles have sensors in their eyes which act as polarising filters.
   
Describe and explain the effect of rotating a polarising filter in front of a source of plane polarised light.

Thx

[Ramprakash]

You are talking abt mj 2009 3b rite?

Ok,

The mean:


Now find the maximum difference:



So, the maximum uncertainty is

do u consider the sign when calculating max difference?thanks

[elemis]

if an equation is given : s=ut+0.5at^2
and we plot a graph of Distance/time with time .. how can we prove that the graph will be a straight line ? 
it is question 9 C of physics specimen paper

http://www.xtremepapers.me/Edexcel/Advanced%20Level/Physics/Specimen/Physics-Practical-Alternative-SAMs.pdf

Re-arranging the equation :

s/t = u + 0.5at²

This conforms with the general equation of a STRAIGHT LINE :

y = mx +c

[The Golden Girl =D]

if an equation is given : s=ut+0.5at^2
and we plot a graph of Distance/time with time .. how can we prove that the graph will be a straight line ? 
it is question 9 C of physics specimen paper

http://www.xtremepapers.me/Edexcel/Advanced%20Level/Physics/Specimen/Physics-Practical-Alternative-SAMs.pdf

S/t = u + 0.5at

u and a are constants

so s/t is directly proportional to t

[The Golden Girl =D]

Q:
Scientists have discovered recently that the dung beetle can navigate using polarised moonlight. The beetles hunt for fresh dung. When they find some each beetle makes a small ball. To keep this ball for itself it needs to remove it quickly. The beetle pushes the ball along with its back legs while moving with its front legs and keeping its head down. Using the plane of the polarised moonlight as a guide lets the beetle run away in a straight line.
The beetles have sensors in their eyes which act as polarising filters.
   
Describe and explain the effect of rotating a polarising filter in front of a source of plane polarised light.

Thx

Which paper is this ?