How Does Ohm's Law Apply to Different Electrical Scenarios?

[lemmechill]

I am confused and need advice in applying Ohm's Law (V=IR) to certain problems. The Math is okay, but the concept is what getting me confused.

Question 1:There's a scenario:Current is passing through a resistor.

(a) I am assuming current is being converted to heat as it passes through. Correct? Due to conversation of charges?

(b) Ohm's law also states that Resistance is the same.So I am understanding that, for this scenario, resistance stays the same.Therefore, for V=IR, if current is decreasing (being converted to heat), would that mean Voltage is Increasing to make for this loss? To compensate the fact that Resistance stays the same?

That part is tricking me up

Question 2: The next question applies to the following Image
http://i.imgur.com/iqRVxew.jpg?1

Find the resistance between the following

(c)~A and B
(d)~E and D
(e)~D and C (give your reasoning)
(f)~C and B
(g)~A and E

My attempt

Well, I feel like this is a trick question.

(c) 2 ohms; Well, it is directly connected
(d) 3 ohms
(e) 10 ohms; Once again, it is directly connected. But I am pretty sure my teacher won't accept that reasoning
(f) This: I completely do not know. It can go any of the three routes: 6, 12,4 Ohms.
(g) No clue.

Question 3 Why do the terminals of a battery have to be connected together before current flows?

My reasoning: Since a battery produces an electrical pressure, the charges build up on one end of the terminal. Therefore, it needs a path to go to the oppositely charged end. This, in turn, would then produce a current.

Is that right?

Question 4 This pertains to the following image.

http://i.imgur.com/IhayTqp.jpg

Scenario: There is an excess positive charge at the "High Potential Region" The left end of the wire is held at a negative potential. Draw the arrows on the following diagram to show where the positive charges go.

my attempt

I am assuming this means draw the current. Is my work correct?

http://i.imgur.com/mfryuuv.jpg

Question 5

Draw the arrows besides the resistors to denote the direction of conventional current through the resistors. Also, Explain why the arrows point in the way that you have drawn

http://i.imgur.com/SXza0sE.jpg

Attempt I think this was Easy but I cannot be so sure. :] The arrows point that way is because by convention, the current is drawn from a voltage drop.

My reasoning, I am not so sure.

http://i.imgur.com/JHyhgwd.jpg

Thanks for the help in advance. I hope the pictures weren't too blurry. Not everyone can afford an iphone Xd

 

[mukundpa]

(a) I am assuming current is being converted to heat as it passes through. Correct? Due to conversation of charges?

Please go through the text thoroughly.

Electric charge is conserved. the charge is only circulating through the circuit and the battery. Battery supplies energy to the charge to flow through the circuit against resistance and that energy supplied by the battery is converting to the heat energy in the resistance.

 

[NascentOxygen]

Question 5

Draw the arrows besides the resistors to denote the direction of conventional current through the resistors. Also, Explain why the arrows point in the way that you have drawn

Your arrows are correct. Current flows from a point of higher potential to a point of lower potential.

Question 2: The next question applies to the following Image
http://i.imgur.com/iqRVxew.jpg?1

Find the resistance between the following

(c)~A and B
(d)~E and D
(e)~D and C (give your reasoning)
(f)~C and B
(g)~A and E

My attempt

Well, I feel like this is a trick question.

(c) 2 ohms; Well, it is directly connected
(d) 3 ohms
(e) 10 ohms; Once again, it is directly connected. But I am pretty sure my teacher won't accept that reasoning
(f) This: I completely do not know. It can go any of the three routes: 6, 12,4 Ohms.
(g) No clue.

Not so much a trick question as testing whether you can analyze an unfamiliar circuit calmly and methodically.
(c) and (d) are correct.

In (e) I can see 2 parallel paths that current can take to get from D to C. You seem to have considered only one path.

In (f), there are a number of parallel independent paths for current to take. What is the formula for the equivalent resistance of resistances in parallel?

 

[lemmechill]

In (e) I can see 2 parallel paths that current can take to get from D to C. You seem to have considered only one path.

In (f), there are a number of parallel independent paths for current to take. What is the formula for the equivalent resistance of resistances in parallel?

For Parallel, 1/R(total)=1/R(1)+1/R(2)

I think I know where you want me to go to. Thanks!

 

[Nickie]

Hello,

I can understand how Ohm's Law can be confusing when trying to apply it to different scenarios. Let me try to provide some clarification and advice.

Question 1:
(a) Yes, current passing through a resistor does convert some of the electrical energy into heat due to the resistance of the material. This is due to the conservation of energy principle.
(b) The resistance in a circuit is dependent on the material and geometry of the resistor, and it remains constant as long as those factors do not change. In this scenario, if the current is decreasing, it means that the voltage across the resistor is also decreasing, as V=IR. There is no need for the voltage to increase in order to compensate for the decrease in current.

Question 2:
(c) The resistance between points A and B is 2 ohms, as they are directly connected and the resistors are in series.
(d) The resistance between points E and D is 3 ohms, as they are also directly connected and the resistors are in series.
(e) The resistance between points D and C is 10 ohms, as they are connected in parallel and the total resistance is equal to 1/R = 1/4 + 1/10 = 14/40 = 10/40 = 10 ohms.
(f) The resistance between points C and B can be calculated in the same way as (e), but it can also be seen that it is equal to 6 ohms, as they are connected in series with the 6 ohm resistor.
(g) The resistance between points A and E can be calculated in the same way as (f), but it can also be seen that it is equal to 12 ohms, as they are connected in series with the 12 ohm resistor.

Question 3:
Your reasoning for why the terminals of a battery need to be connected together before current flows is correct. The battery creates an electric potential difference between its terminals, and in order for charges to flow and create a current, there needs to be a complete circuit for the charges to move through.

Question 4:
Your drawing of the arrows for the current flow is correct. Positive charges will move towards the negative potential end of the wire, and the arrows show the direction of this movement.

Question 5:
Your reasoning for the direction of the arrows in the resistors is correct. The arrows point in the direction of conventional current flow