Confused with circuit that has two opposing emf

[toforfiltum]

@William White Ah ok so current flows in one direction only. Ok thanks. My teacher had me thinking that there were two opposing flow of current in that circuit.

 

[William White]

@William White Ah ok so current flows in one direction only. Ok thanks. My teacher had me thinking that there were two opposing flow of current in that circuit.

I reality there is a sum of currents.

Imagine pushing a block forwards, and your friend pushing it backwards, but with a greater force than you. The total effect is that it will go backwards.

But to know that, you need to keep a track of both forwards and backwards forces.

So, you need to know the currents in both directions so you can know the total current and what direction it flows.

 

[toforfiltum]

I reality there is a sum of currents.

Imagine pushing a block forwards, and your friend pushing it backwards, but with a greater force than you. The total effect is that it will go backwards.

But to know that, you need to keep a track of both forwards and backwards forces.

So, you need to know the currents in both directions so you can know the total current and what direction it flows.

Ah I see. Ok thanks.

 

[William White]

Hmm...then if to follow your logic, say I now have a circuit where the two opposing emfs are equal. Then, there would be a positive value of current and a negative value of current flowing in the circuit. The ammeter reading is zero. But if I were to put my fingers across the wire, I would feel a shock due o the current, no matter where it is flowing.

If you touched a circuit where the sum of voltages was zero you would not feel a shock (as long as you were standing at zero voltage - say on the earth)
Seems counter-intuitive, but when you do AC theory you will see a more practical example. In 3-phase AC system, there are 3 voltages of equal magnitude, but they are 120° out of phase with each other (rather than 180° in your example with 2 sources). When you add them up, the total is zero. This is the neutral point. The currents flow from one line through the neutral into the other lines. As long as the voltages are equal and opposing it is quite safe to touch the neutral point. And in fact, this point is connected to Earth for safety.

 

[toforfiltum]

If you touched a circuit where the sum of voltages was zero you would not feel a shock (as long as you were standing at zero voltage - say on the earth)
Seems counter-intuitive, but when you do AC theory you will see a more practical example. In 3-phase AC system, there are 3 voltages of equal magnitude, but they are 120° out of phase with each other (rather than 180° in your example with 2 sources). When you add them up, the total is zero. This is the neutral point. As long as the voltages are equal and opposing it is quite safe to touch the neutral point. And in fact, this point is connected to Earth for safety.

Haha, this is out of my depth.I don't get the out of phase thing Guess I'm not there yet. Physics is hard to understand intuitively..

 

[William White]

Haha, this is out of my depth.I don't get the out of phase thing Guess I'm not there yet. Physics is hard to understand intuitively..

yes, don't worry about that; it was just an example to say that you can add up "things" of non-zero "size" and get a zero answer so long as the "direction" of the things are different.
Just make the circuit as simple as possible - I think the way of removing all sources except one is an easy way to see what each source is contributing to the total.