Resistor and current in a circuit

[conscience]

Hello ,

I have to teach a group of 9th grade students
role of resistor in a circuit and how it affects the current in the circuit . This will be their first exposition to circuits .So I need a good and simple analogy so that students can grasp these concepts easily .

This is what I plan to teach .

Consider two set ups . In first there is an inclined plane with lots of balls held at the top .Now these balls are allowed to roll down the plane one after another .The number of balls collected per unit time at the bottom is noted , say x balls/sec .

In the second case , there are pegs/ obstructions on the inclined plane such that if a ball is released at the top ,it will reach at the bottom only after bouncing off from the pegs in a zig zag fashion .Again the number of balls collected at the bottom is noted ,say y balls/ sec .

Clearly x>y .

The first case represents a very low resistance wire connected across a battery and the second represents a high resistance connected across a battery .

The height represents potential difference .Balls are electrons , pegs are ions .

A child putting the balls back on top acts like a battery .

It can be seen that similar to the ball example , the current flowing in a circuit with a bigger resistance is lower i.e the resistor reduces the current in a circuit . Bigger the resistance offered , smaller the current .

Is this a decent analogy ? Is there something I am missing or something I need to correct .

Please give your feedback .

Thanks

 

[rumborak]

I think it's an excellent visualization. Usually people go for the "water flowing through narrowing pipes" analogy, but yours is closer to physical reality.

 

[conscience]

Great !

Another question that one of the more curious minds can put is -

" Why/How is current constant in a circuit " ?

This is what I think -

1) Because of law of conservation of charge , charge flowing in per second in any part of the circuit is equal to charge flowing out per second . Current has to be same .

2) Even if we suppose that current is not uniform , then there would be a build up of charge somewhere .This would ensure that faster moving electrons are slowed down whereas slower moving electrons pick up speed .

Alternatively, mutual repulsion of electrons will ensure that electrons are moving with a constant average speed .

Is this a valid explanation ?

 

[cnh1995]

Great !

Another question that one of the more curious minds can put is -

" Why/How is current constant in a circuit " ?

This is what I think -

1) Because of law of conservation of charge , charge flowing in per second in any part of the circuit is equal to charge flowing out per second . Current has to be same .

2) Even if we suppose that current is not uniform , then there would be a build up of charge somewhere .This would ensure that faster moving electrons are slowed down whereas slower moving electrons pick up speed .

Alternatively, mutual repulsion of electrons will ensure that electrons are moving with a constant average speed .

Is this a valid explanation ?

Yes.

And for point no 2, mention that the time of the surface charge build-up is in the order of
10^-10 to 10^-12 s, which is why we see a lightbulb glowing instantly after the switch is closed.

 

[davenn]

2) Even if we suppose that current is not uniform , then there would be a build up of charge somewhere .This would ensure that faster moving electrons are slowed down whereas slower moving electrons pick up speed .

no, this isn't a good way to look at it

electron drift is very slow a few mm per second
the current in a circuit is the number of electrons ( charges) passing a particular point in a circuit at a given time, not how fast they are travelling

 

[davenn]

Yes.

do you want to clarify your simple yes ?
it can't be used as a blanket response for both his comments

 

[cnh1995]

do you want to clarify your simple yes ?

Because of law of conservation of charge , charge flowing in per second in any part of the circuit is equal to charge flowing out per second . Current has to be same .

This is correct.

But initially, when the circuit is closed (say using a switch), this is not true. To make the current same everywhere in the circuit, there are surface charge buildups on the wires and circuit components.

I agree that speed of electrons is not the correct way to visualize current.
Instead, in point no 2, he should say: The surface charges build up because initially, the charges move at different rates, which results in excess positive charge in some parts and excess negative charge in some parts. This process goes on until there is no excess charge in any part of the circuit i.e. charge is flowing at the same rate everywhere.

 

[cnh1995]

of why current in a circuit is constant ?

Do you mean to ask "why current in a series circuit is same everywhere?".
The word 'constant' has different interpretations.

 

[conscience]

Yes.

I am not comparing two different circuits . I just want to explain to somebody why a simple circuit consisting of a battery and a resistor has constant/same current throughout the circuit .

If somebody says , why can't current be different in different parts of a circuit ? What would be an explanation at an elementary level ?

Point 2) to which davenn had objected was an explanation for a hypothetical assumption .

Why number of electrons crossing an area per unit time has to be equal to that in some other part of the circuit ?

 

[cnh1995]

Why number of electrons crossing an area per unit time has to be equal to that in some other part of the circuit ?

The surface charges build up because initially, the charges move at different rates, which results in excess positive charge in some parts and excess negative charge in some parts. This process goes on until there is no excess charge in any part of the circuit i.e. charge is flowing at the same rate everywhere.

 

[conscience]

I might be wrong but I think this is an explanation to how uniform electric field is establiahed within the circuit .

Anyways my audience is 9th graders learning circuits for first time .I think it would be difficult for them to understand .

 

[Tom.G]

Why number of electrons crossing an area per unit time has to be equal to that in some other part of the circuit ?

If there are sidewalls on the inclined plane to eliminate spillage, point out that there are the same number of balls flowing at the bottom as at the top because there is no other place for them to go.

 

[conscience]

no, this isn't a good way to look at it

electron drift is very slow a few mm per second
the current in a circuit is the number of electrons ( charges) passing a particular point in a circuit at a given time, not how fast they are travelling

How about this explanation -

The electrons are moving with approximately uniform average speed .So if I consider a piece of wire and assume that current at its two ends are different than this means that some charge carriers are appearing/disappearing magically .This can't happen .

Is it alright ??

 

[conscience]

If there are sidewalls on the inclined plane to eliminate spillage, point out that there are the same number of balls flowing at the bottom as at the top because there is no other place for them to go.

Ok.

Actually what is troubling me is not the number of balls starting at the top and ending at bottom , but the rate of flow of balls .

I think speed is an important factor .

Do you think students also need to be told beforehand that average speeds of all the electrons in the circuit is same just like same average speeds of all balls on the inclined plane ??

 

[cnh1995]

I might be wrong but I think this is an explanation to how uniform electric field is establiahed within the circuit .

The field is not necessarily uniform.
The surface charge buildup stops only when there is no excess charge in any part of the circuit i.e. rate of flow of charge is same everywhere.

This phenomenon gives you the idea/ explanation to some FAQs from high school students like, as you said, why current is same everywhere?, why doesn't current drop after passing through a resistor?, how do electrons turn on a bend in the circuit or why does the shape of the circuit not matter in circuit analysis? etc.

But since it is their first-time with circuits, this might be difficult for them to understand (they may not be knowing anything about electric field or relevant electrostatics).
So I think you should drop this approach.

 

[Tom.G]

Ok.

Actually what is troubling me is not the number of balls starting at the top and ending at bottom , but the rate of flow of balls .

I think speed is an important factor .

Do you think students also need to be told beforehand that average speeds of all the electrons in the circuit is same just like same average speeds of all balls on the inclined plane ??

I agree that "...the rate of flow of balls" is the key factor.

Since Electron speed is constant in a given medium, I would be careful about how this is presented. I'm afraid your ramp with pegs will have an observably longer transit time than the ramp without pegs. Even though the "electrons bouncing off atoms" explanation is widely used, and understandable, it is an analogy and therefore imperfect.

I originally visualized the demo hardware as a reservoir at the top emptying to an unpopulated ramp. Perhaps you had something else in mind?

If the ramps (w/ & w/o pegs) are initially filled with balls, as a wire is filled with Electrons, the (almost) instantaneous flow at the bottom would more correctly show the immediate current flow in the real world. This would probably require that the demo starts with the ramp horizontal. Then raising the reservoir end to show a battery being connected. Practically, this may require a gate at the ramp bottom and a bit of hand-waving that you can't really raise the reservoir as fast as a switch closes.

edit: p.s. "The electrons are moving with approximately uniform average speed"
This polysyllabic exposition may be a stretch for the vocabularies of some 9th graders.

 

[conscience]

@cnh1995 , @Tom.G

What are your thoughts on post 13 ?

 

[Tom.G]

What are your thoughts on post 13 ?

See my edit to post #16.

 

[conscience]

See my edit to post #16.

OK . But do you find it reasonable ?

 

[davenn]

@cnh1995 , @Tom.G

What are your thoughts on post 13 ?

How about this explanation -

The electrons are moving with approximately uniform average speed .So if I consider a piece of wire and assume that current at its two ends are different than this means that some charge carriers are appearing/disappearing magically .This can't happen .

Is it alright ??

no

I gave you the answer and you quoted it in post #13
why give another incorrect reason in that post ?

 

[conscience]

no

I gave you the answer and you quoted it in post #13
why give another incorrect reason in that post ?

I understand that current is charge flowing past a point per second . But it is the rate of flow and not simply the amount of charge flowing .

So if I start with the assumption that current is different at two different points , how will we refute this assumption while not taking electrons drift speed into account .

Please explain your objection to post 13 .

 

[Tom.G]

The electrons are moving with approximately uniform average speed .

What are your thoughts on post 13 ?

conscience said: ↑
How about this explanation -

The electrons are moving with approximately uniform average speed .So if I consider a piece of wire and assume that current at its two ends are different than this means that some charge carriers are appearing/disappearing magically .This can't happen .

(from: davenn post #20)
Is it alright ??
no

I gave you the answer and you quoted it in post #13
why give another incorrect reason in that post ?
(/davenn)

I think I'm getting into the middle of a dispute here! Ahh, well. Not the first time. (sigh...)

I don't see any conflict between
@conscience in post #13 as "...moving with approximately uniform average speed" and moving at a specific speed that @davenn reported in post #5 as"... a few mm per second."
Perhaps the perceived conflict is from the impracticality of having a ramp for the demo wide enough to accommodate all the electrons in a wire. With this constraint, the balls in the demo will be moving faster than real electrons. This may well be necessary to avoid having the class fall asleep during the demo!

But it is the rate of flow and not simply the amount of charge flowing .

There are at least two interpretations of rate. Specifically, "The rate that a river flows in miles-per-hour" and "the rate the river flows in gallons-per-second."

In Physics, current is defined in terms of Electrons-per-Second, and the miles-per-hour or mm-per-Second is irrelevant to current measurement.

It sounds like different folks are reading the same word and using different definitions.

 

[cnh1995]

So if I start with the assumption that current is different at two different points , how will we refute this assumption while not taking account electrons drift speed .

Drift speed alone is not the correct way to visualize current. You can have 100 electrons drifting with 1mm/s and 50 electrons drifting with 2 mm/s, but both of them give the same current. In a series circuit, the drift speed is different in different components but the current through them is still the same.

 

[conscience]

Drift speed alone is not the correct way to visualize current. You can have 100 electrons drifting with 1mm/s and 50 electrons drifting with 2 mm/s, but both of them give the same current. In a series circuit, the drift speed is different in different components but the current through them is still the same.

I agree .

Do you have a simple explanation as to why should current be the same ?

 

[davenn]

I agree .

Do you have a simple explanation as to why should current be the same ?

cuz what goes into the circuit MUST be the same as what comes out of the circuit. Regardless of what happens within the circuit
If it is a simple series circuit, the current will be measured the same everywhere in the circuit
in a complex circuit, current will be different in different parts BUT overall what goes in is the same as what comes out

imagine a black box ( you DONT know what is inside the box) with 2 wires and an ammeter in each wire.
when you connect it to a power source, the current in each meter will read the same REGARDLESS of what circuitry is inside the black box

 

[davenn]

Drift speed alone is not the correct way to visualize current. You can have 100 electrons drifting with 1mm/s and 50 electrons drifting with 2 mm/s, but both of them give the same current. In a series circuit, the drift speed is different in different components but the current through them is still the same.

and isn't even used in the calculations

I understand that current is charge flowing past a point per second . But it is the rate of flow and not simply the amount of charge flowing .

So if I start with the assumption that current is different at two different points , how will we refute this assumption while not taking electrons drift speed into account .

Please explain your objection to post 13 .

because you don't need to take drift speed into account, you have been told this.
drift speed varies very little unless you are dealing with comparing very small and very large currents

the important information is the quantity of charges flowing NOT their speed

from wiki

The SI unit for measuring an electric current is the ampere, which is the flow of electric charge across a surface at the rate of one coulomb per second. Electric current is measured using a device called an ammeter.[2]

The coulomb (symbol: C) is the International System of Units (SI) unit of electric charge. It is the charge (symbol: Q or q) transported by a constant current of one ampere in one second:
1 C = 1 A ⋅ 1 s Dave

 

[conscience]

cuz what goes into the circuit MUST be the same as what comes out of the circuit.

But why should what goes into per second should be what goes out per second in any arbitrary section of circuit ?

Please consider any portion of the circuit and not specifically from one terminal of battery to other .

 

[davenn]

But why should what goes into per second should be what goes out per second in any arbitrary section of circuit ?

physics doesn't answer why questions ... it's the way it is

https://www.farnamstreetblog.com/2012/01/richard-feynman-on-why-questions/

you put x litres of water into one end of a pipe, x litres will come out the other end ( assuming the pipe is already full)

the same with a bit of wire or a circuit ... it is already at equilibrium
when 500 electrons leave the negative terminal of a battery ( or other power supply) and enter the circuit, it will create an imbalance in the circuit and in the battery (PSU) and via the force from the electric field
those 500 electrons will be moved slowly along the wire/circuit and will get back to the power source to restore equilibrium

 

[Dale]

Anyways my audience is 9th graders learning circuits for first time .I think it would be difficult for them to understand

Why do we need to do complicated analogies with balls bouncing down pegs at all? Why not just teach V=IR?

It is so simple that I don't think it needs an analogy. Even 9th graders can do it. Any analogy is going to be more complicated and less accurate than the real thing.

 

[Dale]

So if I start with the assumption that current is different at two different points , how will we refute this assumption while not taking electrons drift speed into account .

One of the assumptions of circuit theory is that the net charge on any component is 0 at all times. If the current in and out of any component were unequal then that component would have a nonzero net charge.

 

[jbriggs444]

But why should what goes into per second should be what goes out per second in any arbitrary section of circuit ?

One can chase this particular "why" question down one layer further.

If charges go into a section of a circuit more rapidly than they come out then like charges will build up in that section of the circuit. But like charges repel. They repel strongly. You can build up an excess of charge in a section. But that excess is so tiny that it is normally ignored -- unless one is considering capacitors.

Capacitors are specifically constructed to deal with the self-repulsion of like charges by bringing a similar distribution of opposite charges into close proximity.

 

[conscience]

If charges go into a section of a circuit more rapidly than they come out then like charges will build up in that section of the circuit. But like charges repel. They repel strongly. You can build up an excess of charge in a section. But that excess is so tiny that it is normally ignored

Thank goodness !

Something similar ( although incorrect ) I had intended in post 3 .

Could you please review post 3 ?

 

[sophiecentaur]

I have to teach a group of 9th grade students
role of resistor in a circuit and how it affects the current in the circuit .

You need to see what is required in the Curriculum. Any model you use that they can follow will be inaccurate and, if you teach them one inaccurate model and they are tested on another, they may find that they can't get any marks.
It is shocking that anyone should be called upon to teach such stuff at that level but it happens all over the place. Look at past question papers and see what the mark schemes require from the answers. There will be some Key Words that earn marks. Cynical, I know, but it's the least worst approach. The last thing they need is more confusion than necessary, I think. Tell them they will not get it fully and that they will be able to understand more when their Maths is better. I know that deferred gratification is not in fashion . . . . .

edit: p.s. "The electrons are moving with approximately uniform average speed"
This polysyllabic exposition may be a stretch for the vocabularies of some 9th graders.

Perhaps "The electrons don't actually speed up at all, from start to finish. " would do better.

 

[Nugatory]

But why should what goes into per second should be what goes out per second in any arbitrary section of circuit ?
Please consider any portion of the circuit and not specifically from one terminal of battery to other .

The water-in-pipes analogy that @rumborak mentions in #2 of this thread works pretty well for this question.

Suppose there were a part of the circuit in which the flow of charge in was greater than the flow out. Over time, the charge in that area would increase without bound. But because like charges repel, as the charge builds up the force pushing charge out of that part of the circuit also increases, which in turn increases the flow out. So as long as the flow out is less than the flow in, the flow out will increase; this can only end when the two are equal.

 

[conscience]

One can chase this particular "why" question down one layer further.

If charges go into a section of a circuit more rapidly than they come out then like charges will build up in that section of the circuit. But like charges repel. They repel strongly. You can build up an excess of charge in a section. But that excess is so tiny that it is normally ignored -- unless one is considering capacitors.

Capacitors are specifically constructed to deal with the self-repulsion of like charges by bringing a similar distribution of opposite charges into close proximity.

The water-in-pipes analogy that @rumborak mentions in #2 of this thread works pretty well for this question.

Suppose there were a part of the circuit in which the flow of charge in was greater than the flow out. Over time, the charge in that area would increase without bound. But because like charges repel, as the charge builds up the force pushing charge out of that part of the circuit also increases, which in turn increases the flow out. So as long as the flow out is less than the flow in, the flow out will increase; this can only end when the two are equal.

Both the above inputs are quite nice .Thanks a lot

Thank you @rumborak , @Tom.G

 

[conscience]

It is so simple that I don't think it needs an analogy. Even 9th graders can do it. Any analogy is going to be more complicated and less accurate than the real thing.

Your concern is valid and much appreciated .

I feel using analogy is a nice way while introducing something new . Every Introductory Physics texts vis a vis Halliday , University Physics use some or the other kind of analogy while starting with circuits .So I guess I will not be doing something totally absurd .

Most of the discussion in this thread has been related to my second question i.e how do you respond to a smart kid who questions that why should current be constant in the circuit . I neither intended nor mentioned anywhere that I was relating this question to the inclined plane analogy mentioned in the OP .Did I ? I was just looking for a simple explanation .

Why do we need to do complicated analogies with balls bouncing down pegs at all? Why not just teach V=IR?

I have always intended to stick to V=IR .I assure you that I won't stretch the inclined plane analogy too far .Just a rough comparision , then V=IR all the way till the end .

 

[256bits]

The height represents potential difference .Balls are electrons , pegs are ions .
A child putting the balls back on top acts like a battery .
It can be seen that similar to the ball example , the current flowing in a circuit

how do you respond to a smart kid who questions that why should current

be flowing uphill against the potential. Is the raised part of the ramp the negative side of the battery, or maybe its the positive? Can you show side by side diagrams of the peg-ball experiment and v=IR and what matches with what. Shouldn't the balls, acting as electrons, be flowing uphill if the raised part of the ramp is at a higher potential, meaning positive, since the girl is acting as a battery, and a battery acts as a raise in potential, and current flows from positive to negative through the circuit resistance. Or do the balls show current, and the balls hitting the pegs shows current hitting ions. So what is current made up of then, if the opposite direction it is electrons flowing, then the whole thing does not make sense to me anymore and I am totally confused. Can we start over please, as I do not want to be thinking for the rest of my life as current being little balls hitting pegs, or was it electrons hitting pegs going the wrong way, even as a third year university electrical engineering student the vision will come back to haunt me. End Of Student Question.

Sorry to say but like the above student I just don't get it either.

 

[Dale]

I feel using analogy is a nice way while introducing something new . Every Introductory Physics texts vis a vis Halliday , University Physics use some or the other kind of analogy while starting with circuits .So I guess I will not be doing something totally absurd

It isn't absurd at all, but I personally think it is a really bad habit that the community of educators has gotten into. I wish that we would just stop. I think that teachers and textbook writers have perpetuated this habit more to show off their own cleverness than to actually help the students.

I mean, what is the underlying concept that you are trying to teach with the analogy. Presumably it is Ohms law. But trying to analyze randomly bouncing balls is horrendously more complicated than V=IR. Same with fluid mechanics (the other usual analogy), it is an analogy that is far more complicated than the real thing! Why spend valuable class time that way? How does the student benefit? Would they not benefit as much from spending the same time learning the real thing?

My ideal approach would be more hands on and real. I would get a voltmeter and a battery. I would show them how to measure the voltage. I would get a light bulb and show them how to measure current. I would plot voltage and current and show Ohms law physically.

At the end, not only would they understand Ohms law without analogies, but they would have learned some practical stuff that will be useful later in life too.

 

[conscience]

I mean, what is the underlying concept that you are trying to teach with the analogy. Presumably it is Ohms law. But trying to analyze randomly bouncing balls is horrendously more complicated than V=IR. Same with fluid mechanics (the other usual analogy), it is an analogy that is far more complicated than the real thing! Why spend valuable class time that way? How does the student benefit? Would they not benefit as much from spending the same time learning the real thing?

My ideal approach would be more hands on and real. I would get a voltmeter and a battery. I would show them how to measure the voltage. I would get a light bulb and show them how to measure current. I would plot voltage and current and show Ohms law physically.

At the end, not only would they understand Ohms law without analogies, but they would have learned some practical stuff that will be useful later in life too.

Fair enough . You have almost convinced me to drop this analogy thing altogether

How would you introduce the concept of potential difference to 9th graders being exposed to circuits for the first time?

Please note that facility to perform practicals is not available .

 

[Dale]

Please note that facility to perform practicals is not available

I would probably do it as a demonstration. It might depend on classroom size, number of students, and so forth.

 

[NTL2009]

Fair enough . You have almost convinced me to drop this analogy thing altogether

How would you introduce the concept of potential difference to 9th graders being exposed to circuits for the first time?

Please note that facility to perform practicals is not available .

But different people learn differently. If presented with the formula E = I * R, I'd just be "ho-hum, lots of things have that relationship. Eggs = Eggs per carton * cartons. So what makes electricity 'special'? ".

Suggestion for your analogy: String the balls together like a beaded necklace. Instead of pegs, use a channel lined with carpeting, and a means to compress and release the carpet-channel a bit to increase and decrease friction, and pull the string of balls through the channel. This way, all the balls move at the same rate in the 'circuit'.

It even works if you compress one section more than the other. That would be analogous to a 100 Ohm R in series with a 10,000 Ohm R. The balls can't move through the 100 Ohm R any faster than they can through the constricted 10,000 Ohm R, as they are all connected and pulled by the same force.

 

[Nugatory]

How would you introduce the concept of potential difference to 9th graders being exposed to circuits for the first time?

Start with gravitational potential differences instead of electrical. Everyone has a fairly solid intuitive understanding of what it means to be moving "uphill" and "downhill", and topographical maps with curves of equal gravitational potential are readily available and easy to read.

 

[conscience]

Start with gravitational potential differences instead of electrical. Everyone has a fairly solid intuitive understanding of what it means to be moving "uphill" and "downhill", and topographical maps with curves of equal gravitational potential are readily available and easy to read.

Excellent suggestion ! Thanks

Probably one last question

How do you introduce concept of "infinity" while explaining standard definition of electric potential ? Just as the teacher mentions the word "infinity" students are bemused . Questions like what is infinity ,why only infinity , how far is infinity and so on , crop up .

So how do we explain the notion of infinity in context of electric potential ?

 

[cnh1995]

So how do we explain the notion of infinity in context of electric potential ?

Perhaps you'll find @jim hardy's little thought experiment here helpful.

https://www.physicsforums.com/posts/5331150/
https://www.physicsforums.com/posts/5347090/

 

[Ram C]

Great analogy!...
Here are another analogies of series and parallel circuits:
One can clearly compare series and parallel circuits with water flowing analogy. Suppose we have a water tank a some height above the building. Let water is drawn from tank to some terminal at ground through one single pipe. The pipe is then distributed into 3 taps. Line from first tap is going to 2nd tap and then to 3rd tap. This is like series circuit. Because quantity of water (electric current) is same but potential difference is reducing at each tap. You will get lower pressure at last tap while same quantity of water which passed through tap 1. But if you take separate water line for each tap directly from tank, then you will get equal pressure at each tap but with different quantity of water (electric current) according to the diameter of pipe/tap. This is analogous to parallel circuit.

 

[Physics_Kid]

no, this isn't a good way to look at it

electron drift is very slow a few mm per second
the current in a circuit is the number of electrons ( charges) passing a particular point in a circuit at a given time, not how fast they are travelling

passing a point ??
its passing through an area, many times called flux.

i would model it using a block crossing sandpaper on a flat table. the tricky part is to show how the block itself loses energy (eV) as it crosses the sandpaper while keeping constant velocity.

 

[Fernando Perfumo]

Why not you show them the real thing? I bet they will understand it very well and never forget.
Do simple experiments using lamps, batteries, one amperimeter, a couple of voltimeters and a set of long and short or thick and thin wires. Of course use harmless voltages and fuses
I still remember when I was a child a tv series showing laboratory experiments on physics... simple rockets, static electricity... I really liked that.

 

[Quandry]

OK, so here is the crunch question. Nugatory mentioned Curriculum. I will now mention qualified tutors.
It is OK to learn and understand these things, but is it fair on the 9th graders.
There are many teaching aids on the net which I suggest you review. Most of the elementary stuff is for 4th graders.
For example https://www.pbslearningmedia.org/re...e.lp_electric/electric-circuits/#.WXfgysaB3u4

 

[sophiecentaur]

It is OK to learn and understand these things, but is it fair on the 9th graders.

Agreed. Non Scientists, who never really got a grasp of the subject (but who were bright enough in other directions to get influential jobs) like to think that all kids have the potential to understand EM, QM and Thermodynamics so why not hit kids with it as early as possible? They (those politicians) see a way to make their mark by having the education system force feeding the subject at an inappropriate age. Never mind the casualties who, ever afterwards, either find Science incomprehensible or think it's a trivial subject - as presented in popular media. And that is actually the majority of the adult population.
Education, like the Judiciary, should be insulated against political influence. Fat chance of that, though.