2018 June IAL Physics Unit 4 (Edexcel)

Let's discuss our questions/doubts on unit 4 physics here.

Reply 1

OP

Can someone help me with this Lenz's law graph?
I don't know how to determine whether the induced emf is positive or negative.

Reply 2

Kishoth

3

Look at June 2013 paper. It has the same question.So basically as magnet approach there is change in magnet flux and as it leaves there is change in magnetic flux.Direction is due to different direction of magnet.Area under graph npi is constant.The reason was negative effect is larger is because magnet is accelerating.

Reply 3

Can anyone provide me with a precise process of Linac and Cyclotron?

Reply 4

Original post by Vincent Lou

Can someone help me with this Lenz's law graph?
I don't know how to determine whether the induced emf is positive or negative.

I would answer it more or less like this,

- Change of magnetic flux linkage induces an emf in the coil.
- emf proportional to the rate of change of flux linkage
- Initial increase up to A as magnet approaches the coil.
- Negative gradient, A-B to C due to magnet going through the coil.
- After C - is after when the magnet exits and is accelerating away from the coil.
- Negative peak&gt; Postive peak as magnet's speed increases as it falls.
- Area under both peak same as change in magnetic flux linkage is constant.

Optional: As the circuit Is closed a current is produced.

EDIT: Sometimes a question may come in which the graph is reversed, hence this should also be written. - Reverse polarity of emf is due to Lenz's law.

(edited 5 years ago)

Reply 5

Original post by Black.Panther00

Can anyone provide me with a precise process of Linac and Cyclotron?

Cyclotron:
- Particle accelerated by electric field between Dees.
- Inside the Dees particle follow a circular path due to the perpendicular magnetic field present providing the centripetal force required.
- As the particle exits the Dees the field reverses.
- The field reverses at a constant frequency equal to the frequency of circulation of the particles.
- As the particle gains energy, and as r is proportional to Ek, the radius of its path increases as well.

Linac:
- Particles are accelerated by the electric field present between the gaps of successive tubes.
- As particles are in the tube polarity of the field reverses.
- Polarity of the field switches at a constant frequency.
- The length of the tubes gradually gets longer as to ensure the particles spend the same amount of time in each tube.

(edited 5 years ago)

Reply 6

answer is B anyone can explain why ?

P.s I found how the answer came ** Edit**

(edited 5 years ago)

Reply 7

unknown2914

how do you calculate force from a momentum against time graph

Reply 8

Original post by unknown2914

how do you calculate force from a momentum against time graph

Upload the question , it'll be easy to answer then :smile:

Reply 9

pearl02

4

Original post by Black.Panther00

answer is B anyone can explain why ?

P.s I found how the answer came ** Edit**

But why B? :frown:

Reply 10

unknown2914

Original post by Black.Panther00

Upload the question , it'll be easy to answer then :smile:

Reply 11

Original post by unknown2914

Alright its easy you know the formulae of impulse?
its DeltaP = F x t
Delta P is = Final momentum - Initial Momentum
okay so -0.6-0.4 = -1 Ns ? right?
so the time it takes for the rebound is 4x10^-3
now f = -1/4x10^-3
which is = -250 N

Reply 12

unknown2914

Original post by Black.Panther00

Alright its easy you know the formulae of impulse?
its DeltaP = F x t
Delta P is = Final momentum - Initial Momentum
okay so -0.6-0.4 = -1 Ns ? right?
so the time it takes for the rebound is 4x10^-3
now f = -1/4x10^-3
which is = -250 N

I get it
Thank you

Reply 13

OP

From 2014JAN

Marking Scheme:
The build-up of charge creates an electric field
This creates a force in the opposite direction to the magnetic force

Can someone explain what is the answer saying? I don't get it at all..

Reply 14

Original post by pearl02

But why B? :frown:

Reply 15

Original post by sexypelic4n

Thanks

Reply 16

Original post by Vincent Lou

From 2014JAN

Marking Scheme:
The build-up of charge creates an electric field
This creates a force in the opposite direction to the magnetic force

Can someone explain what is the answer saying? I don't get it at all..

This is how I perceived it:

This is an application of Hall p.d. basically. The magnetic force causes the electrons to move towards the left wing, so it is negatively charged and the right wing is positively charged. This creates an electric field.
This field produces a force, F=Ee which balances Bev.

Reply 17

OP