Electronics question help-E,I,R

Papabravo

Joined Feb 24, 2006
19,836
Hint: Ohm's Law tells you how three particular quantities in a circuit are related. What you need to know is that if you know the value of any two of the three quantities, the third quantity is uniquely and precisely determined. Does that help?

Read and absorb the following article. Then reread it until the light bulb goes on!
https://en.wikipedia.org/wiki/Ohm's_law
 

MrChips

Joined Oct 2, 2009
28,115
"What minimum current in milliamps must the op-amp be able to supply so that Vo(t) = Vin(t)?"

This is either a badly worded question or a trick question.
Unless you have a good knowledge of the English language it would be difficult to answer this question.
 

Papabravo

Joined Feb 24, 2006
19,836
"What minimum current in milliamps must the op-amp be able to supply so that Vo(t) = Vin(t)?"

This is either a badly worded question or a trick question.
Unless you have a good knowledge of the English language it would be difficult to answer this question.
Just eliminate the word minimum since the answer is unique.
 

MrSalts

Joined Apr 2, 2020
2,767
"What minimum current in milliamps must the op-amp be able to supply so that Vo(t) = Vin(t)?"

This is either a badly worded question or a trick question.
Unless you have a good knowledge of the English language it would be difficult to answer this question.
It's a very straight-forward question. They are asking the reader to incorporate three concepts at once,
- the gain of the amplifier,
- application of ohms law, and
- how to convert amps to milliamps.
 

MrChips

Joined Oct 2, 2009
28,115
So if we remove the catch words the question becomes:

"What current must the op-amp be able to supply so that Vo(t) = Vin(t)?"
 

MrSalts

Joined Apr 2, 2020
2,767
So if we remove the catch words the question becomes:

"What current must the op-amp be able to supply so that Vo(t) = Vin(t)?"
If you are willing to accept any current value greater that or equal to the minimum, or willing to spend time arguing with students abiut why an answer above the minimum is wrong, yes. The experienced professor who added the word "minimum" (and underlined it) knows how to write a question with only one correct answer.
 

WBahn

Joined Mar 31, 2012
28,166
Just eliminate the word minimum since the answer is unique.
The problem is NOT the word minimum, its the word milliamp. It has no place there, since the problem can only be answered symbolically and symbols carry their own units.

This is like saying that the height of an underpass is H and regulations require margin of at least D for a vehicle passing under it, so what is the maximum height of the a truck, in inches, that can legally pass under the bridge. It is improper to assume some arbitrary unit for H and D, at least not without specifying it explicitly as part of the answer.

The word "minimum" is redundant because of the presence of the word "must". But it doesn't do any harm and is a more explicit specification for many people.
 

WBahn

Joined Mar 31, 2012
28,166
So if we remove the catch words the question becomes:

"What current must the op-amp be able to supply so that Vo(t) = Vin(t)?"
If you are willing to accept any current value greater that or equal to the minimum, or willing to spend time arguing with students abiut why an answer above the minimum is wrong, yes. The experienced professor who added the word "minimum" (and underlined it) knows how to write a question with only one correct answer.
So you are saying that if V were to be 10 V and R were to be 100 kΩ, that you would accept as a correct answer someone saying that the opamp MUST be able to supply 100,000 mA of current?
 

MrSalts

Joined Apr 2, 2020
2,767
The problem is NOT the word minimum, its the word milliamp. It has no place there, since the problem can only be answered symbolically and symbols carry their own units.

This is like saying that the height of an underpass is H and regulations require margin of at least D for a vehicle passing under it, so what is the maximum height of the a truck, in inches, that can legally pass under the bridge. It is improper to assume some arbitrary unit for H and D, at least not without specifying it explicitly as part of the answer.

The word "minimum" is redundant because of the presence of the word "must". But it doesn't do any harm and is a more explicit specification for many people.
V is clearly volts, R is clearly ohms, so I must be Amps and I * 1000 would be milliamps. At least that's how I would grade it and I'm sure you'll find a reason to call everyone else wrong.
 

MrSalts

Joined Apr 2, 2020
2,767
So you are saying that if V were to be 10 V and R were to be 100 kΩ, that you would accept as a correct answer someone saying that the opamp MUST be able to supply 100,000 mA of current?
I didnt say I would. I am just plenty aware of how students think when they are struggling to get ever possible point they can get. Clear questions result in clear answers and don't waste my time. Do you understand?
 

WBahn

Joined Mar 31, 2012
28,166
I didnt say I would. I am just plenty aware of how students think when they are struggling to get ever possible point they can get. Clear questions result in clear answers and don't waste my time. Do you understand?
You're the one that said that any answer above the minimum would have to be accepted if the question was worded that way. So what are you saying now? That you might not accept an answer that you said would have to be accepted?
 
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