Year 12s: what will be the first way you research your future options? >>

OCR Physics A G485 - Frontiers of Physics - 18th June 2015

Scroll to see replies

Reply 1300

kate8

relative sizes of atom and nucleus?

Reply 1301

boristeve

Original post by Jim997

Mass spectrometers. Please I beg

Used to determine the masses of charged ions and their relative abundances.

- A uniform magnetic field is used to deflect the charged ions in a circular path in an evacuatedchamber.

- A moveable detector used to find the radius of the path and the relative abundance of the ions.

- The radius r of the path in the magnetic field region is 𝑟 =𝑚𝑣/𝐵𝑄.

- The radius that the particle moves in (and hence the place where it hits the sensor) depends on thedifferent mass to charge ratio.

so frickin scared

Original post by kate8

relative sizes of atom and nucleus?

Nucleus is ~1/10,000th of the atom.

Reply 1304

JayGreen

Original post by I Persia I

Nucleus is ~1/10,000th of the atom.

atom is 10^-10m
nucleus is 10^-14m
proton/neutron is 10^-15m
electron < 10^-18m

Reply 1305

coder4

Some guide me please;
When you have both and electric field and magnetic field, how do you work out the direction of movement of an electron in both fields? :smile:

Reply 1306

ETRC

Original post by nothepreacher

Ions travel through a velocity selector, where E and B can be controlled, so that ions passing straight into another magnetic field region B2 have a velocity E/B. The radius of the circular motion is mE/B1B2q. Once r is determined, the mass to charge ratio of the ions can be determined. I am not too sure actually. Can someone correct me?

where did you get mE/B1B2q from?

Reply 1307

jcwh97

Original post by randomuser1

Just did a past paper which included having to work out the momentum of an electron with a wavelength.E = hc/lambda also comes up when pair production occurs.

Yeah I meant when referring to waves etc. it will only be the quantum physics chapters. Nothing more like interference etc. Just the standard equations

Reply 1308

JayGreen

Original post by ETRC

where did you get mE/B1B2q from?

pretty sure its in the textbook, ive seen it and have it written down

Reply 1309

nothepreacher

Original post by ETRC

where did you get mE/B1B2q from?

B1 is the field in velocity selector where there is also E. So v=E/B1. In the second magnetic field region, the force on the ion is B2qv. Equate this to mv^2/r. But v can be expressed in terms of the field strengths as mentioned.

Reply 1310

username2041273

Has anyone got the 2014 paper?!

(edited 8 years ago)

Reply 1311

ETRC

i forgot mass spectrometer existed ffs more stuff to go over

Reply 1312

jcwh97

Original post by ETRC

where did you get mE/B1B2q from?

http://www.st-ambrosecollege.org.uk/library/client/documents/Science/A2%20Physics/G485%205.1.2%20Magnetic%20Fields%20b.pdf

Reply 1313

nothepreacher

Original post by JB199612

Has anyone got the 2015 paper?!

Lol we wish!

Reply 1314

nothepreacher

Original post by ETRC

i forgot mass spectrometer existed ffs more stuff to go over

Got plenty of time dw!

Reply 1315

Malgorithm

Original post by coder4

Some guide me please;
When you have both and electric field and magnetic field, how do you work out the direction of movement of an electron in both fields? :smile:

If the fields are acting in opposite directions to each other:

When E > B, the path of the ions will curve in the direction of the electric field.
When B > E, the path of the ions will curve opposite to the direction of the electric field.
When E = B, the ions will move in a straight path.

(edited 8 years ago)

velocity selector.jpg59.0KB

Reply 1316

username2041273

yeah my bad, i meant does anyone has the 2014 paper?!

Reply 1317

nothepreacher

Original post by jcwh97

Yeah I meant when referring to waves etc. it will only be the quantum physics chapters. Nothing more like interference etc. Just the standard equations

So I shouldn't waste my time going through diffraction patterns or interference right now?

Reply 1318

ETRC

Original post by nothepreacher

Got plenty of time dw!

dw just went over it now- it's pretty simple
i'm better at maths than explanations so this was fine

Reply 1319

leroythelost

A few exam style questions on specific topic in link below. OCR is at the bottom, if anyone wants to do more questions.

http://www.physicsandmathstutor.com/a-level-physics-papers/ocr-unit-5-by-topic/