ohms law proportional

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johnstanleyelectric

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Location
ocala fl.
Hello forum, this is my first time on here so please bear with me. I was taking a test off of the " SNAPS CD" . while on there i came to this question. " If the contacted resistance of a connection increases, and the current of the circuit (load) remains the same, the voltage dropped across the connection will ________. ( I know the answer is increase. but i am having a hard time understanding this. i know that I is equal to E. and that I is equal to 1/R. or inversely proportional to R. but if you raise the resistance then the amps will lower. am i missing something? please help.... thank you.
 
Besoeker

Besoeker

Senior Member
Location
UK
johnstanleyelectric said:
Hello forum, this is my first time on here so please bear with me. I was taking a test off of the " SNAPS CD" . while on there i came to this question. " If the contacted resistance of a connection increases, and the current of the circuit (load) remains the same, the voltage dropped across the connection will ________. ( I know the answer is increase. but i am having a hard time understanding this. i know that I is equal to E. and that I is equal to 1/R. or inversely proportional to R. but if you raise the resistance then the amps will lower. am i missing something? please help.... thank you.
Click to expand...

Welcome first time poster!
An exam question possibly?
It is not considered good form here to answer exam questions for others. Just to give a gentle shove - hopefully in the right direction.
So think about the intent of the question.
Sure, if total circuit resistance increases and the voltage applied remains the same, current will reduce.
But put this in the context of the question. The resistance of a connection. A connection. How significant do you think that is relative to total resistance of the circuit?
Then think why that question is being asked.
You know the answer is increase. What are the consequences?
 
Little Bill

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
johnstanleyelectric said:
Hello forum, this is my first time on here so please bear with me. I was taking a test off of the " SNAPS CD" . while on there i came to this question. " If the contacted resistance of a connection increases, and the current of the circuit (load) remains the same, the voltage dropped across the connection will ________. ( I know the answer is increase. but i am having a hard time understanding this. i know that I is equal to E. and that I is equal to 1/R. or inversely proportional to R. but if you raise the resistance then the amps will lower. am i missing something? please help.... thank you.
Click to expand...

"I is equal to E" you want to explain how you come up with that?
Maybe you meant "I is equal to E/R".

You have to read the context of the question. Do as Besoeker said, look at the word connection and not the total resistance of the circuit. Also, total voltage didn't increase, the voltage drop is what they are talking about.

Welcome to the Forum!
 
Smart $

Smart $

Esteemed Member
Location
Ohio
Since all three are variables, I find it easiest to understand the proportional relationships when one is constant, to rearrange the equation so the "constant" variable is by itself. If the other two variables 'multiply' they are inversely proportional; if they divide, they are directly proportional.

E=IR
E/I=R
E/R=I
 
kwired

kwired

Electron manager
Location
NE Nebraska
johnstanleyelectric said:
Hello forum, this is my first time on here so please bear with me. I was taking a test off of the " SNAPS CD" . while on there i came to this question. " If the contacted resistance of a connection increases, and the current of the circuit (load) remains the same, the voltage dropped across the connection will ________. ( I know the answer is increase. but i am having a hard time understanding this. i know that I is equal to E. and that I is equal to 1/R. or inversely proportional to R. but if you raise the resistance then the amps will lower. am i missing something? please help.... thank you.
Click to expand...
I have a problem with the question. If contact resistance changes, how can current remain the same, unless the voltage of the supply changes at the same time in the same proportion? If you insert a resistance in a series circuit you will have a voltage drop across that resistance. You will also have a change of current in the series. With an inductive load the current could actually increase, but either way current will change when inserting a resistance.
 
Little Bill

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
kwired said:
I have a problem with the question. If contact resistance changes, how can current remain the same, unless the voltage of the supply changes at the same time in the same proportion? If you insert a resistance in a series circuit you will have a voltage drop across that resistance. You will also have a change of current in the series. With an inductive load the current could actually increase, but either way current will change when inserting a resistance.
Click to expand...

I will agree, I don't like the question either. But no where do I see that says the circuit is a series circuit.
 
K8MHZ

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
The OP's question is like many I have seen that people tend to over-think.

If the contact's resistance increases and the supply voltage stays the same, the current will decrease. But the question says the current does not change. In order for both the current to remain the same and have the voltage drop across the contact increase, the supply voltage must also increase. Nothing in the question says that the supply voltage stays the same.

Too many of us are trying to piece together a simple real world example circuit that would be of assistance explaining the answer. If it's assumed the supply voltage AND the current remain the same with an increase in resistance, such an example would be tough to come up with.
 
F

fmtjfw

Senior Member
Location
Fairmont, WV, USA
K8MHZ said:
The OP's question is like many I have seen that people tend to over-think.

If the contact's resistance increases and the supply voltage stays the same, the current will decrease. But the question says the current does not change. In order for both the current to remain the same and have the voltage drop across the contact increase, the supply voltage must also increase. Nothing in the question says that the supply voltage stays the same.

Too many of us are trying to piece together a simple real world example circuit that would be of assistance explaining the answer. If it's assumed the supply voltage AND the current remain the same with an increase in resistance, such an example would be tough to come up with.
Click to expand...

Not with a constant current load.
 
Besoeker

Besoeker

Senior Member
Location
UK
kwired said:
I have a problem with the question. If contact resistance changes, how can current remain the same, unless the voltage of the supply changes at the same time in the same proportion?
Click to expand...
The clue is the resistance of a contact.
How much difference will that make to the circuit being switched by that contact.
The question as I see it is aimed at the effects of contact resistance increasing.
Perhaps there was a follow on question relating to that.
Maybe the OP can come back on that.
 
Little Bill

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
Besoeker said:
The clue is the resistance of a contact.
How much difference will that make to the circuit being switched by that contact.
The question as I see it is aimed at the effects of contact resistance increasing.
Perhaps there was a follow on question relating to that.
Maybe the OP can come back on that.
Click to expand...

Side question.....
What time is it in the UK where you are at?
 
kwired

kwired

Electron manager
Location
NE Nebraska
Little Bill said:
I will agree, I don't like the question either. But no where do I see that says the circuit is a series circuit.
Click to expand...
No it does not. But unless I am reading it wrong this is about a (non specified) connection that has developed some resistance. It is going to be in series with something. Could be at a device, could be just a wire nut. If there is another parallel path the question makes even less sense. If resistance of a parallel component goes up current will still go down in that portion of the parallel path but will go up in the other parallel path(s), if we are talking just switches, wire connectors or other virtually no resistance components then the load still sees same current, it just has a higher percent through those other paths and less through the failing path.
 
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