Do the answers and diagram in these exam questions contradict each other?

[jsmith613]

Do these two answers contradict each other:

Q1) Four students are discussing a circuit. The circuit is in series and contains a lamp, an ammeter and a 10V battery.

Andy: the current in the lamp consists of negative charges moving from the negative batter terminal towards the positive battery terminal

Brandon: THe current in the lamp is a mixture of positive and negative ions

Charlie: the current in the lamp consists of negative charges moving towards the positive battery terminal and positive charges moving towards the negative battery terminal

Denzil: The lamp lights up when two different flows of charges crash into eachoher

Only one sutdent is correct

Answer: Andy is correct

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Q2)
Darren uses a solar panel to charge a battery.
The circuit consists of two cells, one positive and the other negative.
Diagram: http://s359.photobucket.com/albums/oo40/jsmith613/?action=view&current=AdQ.png

The current in the wire is a flow of
a) negative electrons into the positive terminal of the battery
b) negative electrons out of the positive terminal of the battery
c) positive electrons into the positive terminal of the battery
d) positive electrons out of the positive terminal of the battery

Answer: B

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Firstly, don't the answer from Q1 and Q2 contradict each other
Secondly, doesn't the diagram in Q2 contradict the answer

NOTE: these questions are from papers in the same exam series

 

[Hyperspace2]

Do these two answers contradict each other:

Q1) Four students are discussing a circuit. The circuit is in series and contains a lamp, an ammeter and a 10V battery.

Andy: the current in the lamp consists of negative charges moving from the negative batter terminal towards the positive battery terminal

Brandon: THe current in the lamp is a mixture of positive and negative ions

Charlie: the current in the lamp consists of negative charges moving towards the positive battery terminal and positive charges moving towards the negative battery terminal

Denzil: The lamp lights up when two different flows of charges crash into eachoher

Only one sutdent is correct

Answer: Andy is correct

-----------
Q2)
Darren uses a solar panel to charge a battery.
The circuit consists of two cells, one positive and the other negative.
Diagram: http://s359.photobucket.com/albums/oo40/jsmith613/?action=view&current=AdQ.png


Nothing contradicted dear


The current in the wire is a flow of
a) negative electrons into the positive terminal of the battery
b) negative electrons out of the positive terminal of the battery
c) positive electrons into the positive terminal of the battery
d) positive electrons out of the positive terminal of the battery

Answer: B

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Firstly, don't the answer from Q1 and Q2 contradict each other
Secondly, doesn't the diagram in Q2 contradict the answer

NOTE: these questions are from papers in the same exam series

Nothing contradicted dear

1) In question 1, the battery is discharging
2) In fig 2, the battery is charged with solar panel.


when battery discharges , the chemical reaction is at one direction,
now since battery finishes all of chemical materials doing this,
Now chemical materials are turned into something new.
So to get back that new materials into old materials, backward chemical reaction is needed(from new to old materials) ofcourse same current direction won't work, so it is like this.
Hope u did understand.

 

[stevenb]

Secondly, doesn't the diagram in Q2 contradict the answer

I agree with the above answer.

Just to clarify this aspect of your question. The diagram shows an arrow for current direction which is opposite of the electron flow, but this is apparently using conventional current flow as the assumption, which is typical. Conventional current direction (as opposed to electron flow direction) is the direction of positive charge flow. If electrons travel left, then conventional current is to the right. It's just a mathematical equivalence kind of thing, but it's a little confusing until you get used to it.

 

[johng23]

That convention is so stupid, it's just a holdover from when people thought positive charges moved. I understand that it would be annoying to switch everything back (and maybe even dangerous in some situations), but are we just going to keep drawing currents backwards until the end of time?

 

[diazona]

Probably, or at least until civilization collapses and begins to rebuild itself, then maybe when physics is reinvented they'll get it right

http://xkcd.com/567/

Anyway, Hyperspace2 and stevenb are right, things work "backwards" in the second diagram because the battery is being charged, not discharged.

 

[K^2]

That convention is so stupid, it's just a holdover from when people thought positive charges moved. I understand that it would be annoying to switch everything back (and maybe even dangerous in some situations), but are we just going to keep drawing currents backwards until the end of time?

It doesn't matter what charges actually flow. Current is defined as flux of positive charge not because people thought that the positive charges make up the flow, but because it makes sense with all of the other math. Look at the Lorentz Force. Look at Maxwell's Equations. These require current to be defined as flow of positive charge. Changing the convention would introduce an unnecessary minus sign into every single one of these.

Then there is the argument of handedness. A lot of conventions would go from being right-hand to being left-hand. Since right-hand conventions are used for pretty much everything, it would be extremely inconvenient to suddenly have left-hand rules when you introduce a current.

Finally, there are a lot of systems where current really is a flow of positive charges. Consider ion flows in solutions under applied electric field.

Now, the charge of electron is arbitrary. If you want to define electrons as having positive charge, that would have no consequence except for some changes related to parity. But changing sign convention for electric charge simply because negative charges happened to be the current carriers in conductors seems like a very silly proposition.

 

[johng23]

I've been owned.