Why is my calculated resistance higher than the resistor used

[Daniel2244]

I was using two DMM. This is what i measured first: https://gyazo.com/17a884fa585110099230f23d37cce97a, 2nd https://gyazo.com/8ab36f26795166dabfdc9c96355e57c5, 3rd https://gyazo.com/99abb7763af79d616f56a7b061654dd1, 4th https://gyazo.com/3e6d5e53d2e4b6c4888b4b0bf6de0c3a, 5th https://gyazo.com/6219ca3fab9ae1bc758dc0af568de37b

 

[gneill]

Your ammeters don't appear to be placed in series with the resistors that you're measuring the voltage across

 

[Daniel2244]

Your ammeters don't appear to be placed in series with the resistors that you're measuring the voltage across

Does that really matter? because I am using voltage from power supply over the voltage on the branch

 

[gneill]

Does that really matter? because I am using voltage from power supply over the voltage on the branch

It should be okay if the meters are essentially ideal. But we are trying to find the source of your discrepancies, so it would be nice to see the branches handled separately. However, let's see what we can make of the measurements that you took.

What were the V and I readings for these two setups:

Were the current values different? Did you have to adjust the source voltage after moving the ammeter and voltmeter?

 

[Daniel2244]

What were the V and I readings for these two setups

First: VM1=1v, A1 =3.70 second: VM1=0.94v A1=13.22

 

[gneill]

First: VM1=1v, A1 =3.70 second: VM1=0.94v A1=13.22

Don't you find that odd? If the meters were ideal, shouldn't the readings be the same for both setups?

 

[Daniel2244]

Don't you find that odd? If the meters were ideal, shouldn't the readings be the same for both setups?

of course I do, but I don't know why my results have turned out how they have as my circuit was accurately built. Unless they were faulty connection with the wires (which are terrible).

 

[gneill]

Even relatively shabby cables should behave okay for the low currents and potentials involved. Did readings vary wildly with mild jostling of the wires?

The type of things that go wrong in these sorts of labs, even when all the circuit connections are correct and to spec, are related to the measuring equipment and its use. Things such as:

- Inappropriate range selection (affects reading accuracy)
- Choosing and AC range rather than a DC range (or vice versa)
- Incorrect meter connections (set of jacks for the various reading types)
- Meter's internal batteries are failing
- Meter is actually out of calibration or broken due to a previous misuse by another user (it happens!)

I think I would really very much like to see photos of the lab setup for at least two of the arrangements where you record the readings. A closeup of the meters while connected would be fantastic.

 

[Daniel2244]

I think I would really very much like to see photos of the lab setup for at least two of the arrangements where you record the readings. A closeup of the meters while connected would be fantastic

I will provide photographs when I redo this experiment.
I am not sure what went wrong as I set my DMM to DC and power pack DC. However, the other points are valid but I'm not quite sure what you mean by "set of jacks for the various reading types"

 

[gneill]

I will provide photographs when I redo this experiment.
I am not sure what went wrong as I set my DMM to DC and power pack DC. However, the other points are valid but I'm not quite sure what you mean by "set of jacks for the various reading types"

Remember when I asked whether or not your DMM had different places to plug the leads into it for different types of readings or ranges? Sometimes it's easy to forget to change or select the right plug positions.

 

[Daniel2244]

Remember when I asked whether or not your DMM had different places to plug the leads into it for different types of readings or ranges? Sometimes it's easy to forget to change or select the right plug positions.

Yeah, now I understand, the wires I used were placed in the right sockets I'm pretty sure.