OCR Physics A G482, Electrons, Waves and Photons, 25th May 2012

Jan 2012 was 73/100 for an A but was marginally easier and it will have been pulled up by re-sitters.
69/100 is my bet.

Reply 982

Lindizya

^ i think the grade boundaries will be higher for some reason

Reply 983

For the LED question on resistance after 1.8V, was it a straight line?!? I checked against my ruler and even calculated resistance at 1.9V and 2.0V and the resistance was clearly decreasing. Yet quite a lot of my friends said it was a straight line and so R is constant. However they did not check like I did.

Someone shed some light on this for me.

Reply 984

Z REFAN Z

answers as i remember it

last question got exactly 50... but i think its completely wrong did 1 squared +0.8 squared +0.6 squared over 0.2 squared LOL?
Electrons have charge and can be deflected by magnetic and electric fields.
For microwave question Maxim intensity when the detector is parallel to the plane of polarization of the wave aka 0 degrees. Minim intensity is when the detector is perpendicular to the plane of polarisation.
Electrons -maximum kinetic energy question. Electrons have a range of kinetic energies due to collisions between themselves and the atoms of the metal. Maximum kinetic energy cannot be greater than the photon energy minus the work function of the metal.
seven pence that kilowatt hour question
LED's have a longer working life time than filament bulbs because they are versatile and robust. XD
Definition questions look in book xD
2Nd last question i got 30mm because the wavelength was a quarter of the length because it said the length between maximum (anti node) and minimum (node) so 4 x 7.5mm = 30mm
For the number of slits i got 301 mm(some other unit) for something like 3.06 x 10 to minus 6 meters convert that into millimeters then do the inverse to get the number.
The blue wavelength line was about 8 degrees to the horizontal so drew a line inside the other lines.

Reply 985

It was decreasing.
It was non-ohmic due too the straight line not passing through the origin.
I think that will catch a lot of people out.

Reply 986

blossomx

20

Original post by J.C

For the LED question on resistance after 1.8V, was it a straight line?!? I checked against my ruler and even calculated resistance at 1.9V and 2.0V and the resistance was clearly decreasing. Yet quite a lot of my friends said it was a straight line and so R is constant. However they did not check like I did.

Someone shed some light on this for me.

I put that it was decreasing, too. It said to use the graph to support your answer so I also did R=V/I at 2V to show it had decreased.

Reply 987

James_Rogers

I said electrons carry charge, photons carry energy?

This was posted from The Student Room's iPhone/iPad App

Reply 988

Toshiya

1

Original post by J.C

For the LED question on resistance after 1.8V, was it a straight line?!? I checked against my ruler and even calculated resistance at 1.9V and 2.0V and the resistance was clearly decreasing. Yet quite a lot of my friends said it was a straight line and so R is constant. However they did not check like I did.

Someone shed some light on this for me.

This got me as well. I ended up putting it was ohmic because it was a straight line, though I did do some calculations and saw it was clearly decreasing... I was so confused!

Reply 989

Lindizya

oh damn i said it was constant :mad:

Reply 990

blossomx

20

How did you do the question about proving the electron's speed was 4.7x10 to the power of something>?

Reply 991

pixelfrag

11

Original post by Z REFAN Z

answers as i remember it

last question got exactly 50... but i think its completely wrong did 1 squared +0.8 squared +0.6 squared over 0.2 squared LOL?

The waves were 0.8a and 0.6a so when superimposed, the max amplitude you could get waas 0.8a + 0.6a = 1.4a and 0.8a - 0.6a = 0.2a

You know that intensity is proportional to amplitude squared (I = a^2) so:

1.4^2 / 0.2^2 = 49

49 is nearly 50 :smile:

Reply 992

Original post by LeaX

I put that it was decreasing, too. It said to use the graph to support your answer so I also did R=V/I at 2V to show it had decreased.

Yeah exactly, I think it's just my friends rushing and not properly checking just because it looks straight from a far. Not sure how to get the 3 marks though, think I may have just got 2.

Reply 993

root(electron energy from part 1 divided by half * 9.11*10^-31)

Reply 994

Original post by LeaX

How did you do the question about proving the electron's speed was 4.7x10 to the power of something>?

Make the energy from the previous bit equal to 1/2mv^2

Reply 995

pixelfrag

11

Original post by Lindizya

oh damn i said it was constant :mad:

I said it was constant too!
I calculated at random points and got a decreasing resistance, but when using my ruler I saw a straight line and didn't know what to pick so I just said it was constant cause straight line -.-

Reply 996

Lindizya

Original post by LeaX

How did you do the question about proving the electron's speed was 4.7x10 to the power of something>?

you had the kinetic energy from the previous question then equate to k.e= 1/2mv^2 to find what v is.

Reply 997

Original post by J.C

Yeah exactly, I think it's just my friends rushing and not properly checking just because it looks straight from a far. Not sure how to get the 3 marks though, think I may have just got 2.

The line was straight however it didn't pass through the origin so wasn't an ohmic conductor. Rather an obscure easy to forget fact.

Reply 998