electricity question

[Oh_Gee]

from GS-7

for #35, shouldn't E (electric field) be pointing down since convention says electric field lines are drawn from + to -? E=F/q so the Force of E should also be pointing down right? unless question is referring to Force on the electron


for #36, my right hand rule is this
1. thumb is direction of Current(+ to -)
2. index finger is B
3. middle finger/palm is Force

so I understand for this problem my thumb should be pointing down but I'm having trouble understanding where force is pointing

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[Cawolf]

35)

The E field is pointing down (by convention) but because the charged particle is an electron (negative charge), it will be attracted to the positive plate - the question is asking for the direction of electric force.

36)

v = left to right, the direction of electron movement
F = we want it to cancel the electric field, so it points the opposite direction of the E field, upwards

I use v x B = F (v is index, B is middle, F is thumb).

So I would point my index right, thumb up, and see that my middle finger points into the page.

 

[Oh_Gee]

35)

The E field is pointing down (by convention) but because the charged particle is an electron (negative charge), it will be attracted to the positive plate - the question is asking for the direction of electric force.

36)

v = left to right, the direction of electron movement
F = we want it to cancel the electric field, so it points the opposite direction of the E field, upwards

I use v x B = F (v is index, B is middle, F is thumb).

So I would point my index right, thumb up, and see that my middle finger points into the page.

35. oh wait i just remembered if it's a (-) charged particle you just reverse the direction for whatever you're trying to find. is that what i should've done in this question. so the question is asking for the force on the electron specifically? not Force of the electric field?


36. wait shouldn't v(aka electric field) be pointing downward like the answer says?

 

[Cawolf]

It is asking for the force on the particle by the electric field.

Question 36 does not involve the E field, other than knowing we want the force of the B field to oppose it. Since the E field points down, the force from the B field must point up to cancel it.

 

[Oh_Gee]

It is asking for the force on the particle by the electric field.

Question 36 does not involve the E field, other than knowing we want the force of the B field to oppose it. Since the E field points down, the force from the B field must point up to cancel it.

35. looking at the passage, E=electric field so doesn't that imply FE = force of the electric field

36. so the variables we need are F,B,and V?
what does E give us?

 

[Cawolf]

35. Yes - that is why the direction of the electric force is opposite the direction of the electric field.

36. The direction of the E field tells you that you want the direction of the magnetic force to point opposite (up).

 

[Oh_Gee]

35. Yes - that is why the direction of the electric force is opposite the direction of the electric field.

36. The direction of the E field tells you that you want the direction of the magnetic force to point opposite (up).

35. so electric force always points opposite of electric field

36. and Fb always points opposite E field?

man i'm slipping. i feel like i should know these things

 

[Cawolf]

I am sorry to say, but both of the things in last your post are . . .not really accurate.

I think you should rethink it or reread the posts because we have said the solution a few times.

35. No. The negatively charged particle is attracted to the positive plate so the force is upwards (not always).

36. No. The force of the B field has no correlation to the direction of the independent E field. In this problem, we want to them to cancel, so yes.

 

[Oh_Gee]

I am sorry to say, but both of the things in last your post are . . .not really accurate.

I think you should rethink it or reread the posts because we have said the solution a few times.

35. No. The negatively charged particle is attracted to the positive plate so the force is upwards (not always).

36. No. The force of the B field has no correlation to the direction of the independent E field. In this problem, we want to them to cancel, so yes.

oh wait sorry i just re read the question and its asking you to cancel the 2 forces and i guess i didnt catch that

but earlier you said

v = left to right, the direction of electron movement

i thought for the questions we usually reverse V if it's a negative particle

 

[Cawolf]

Yes, but since we are just looking at the fields to determine how they would cancel.

You get the same answer either way, but technically you are correct.