Measuring resistance - variables? (1 Viewer)

[idling fire]

What would the dependent and independent variables be for an experiment measuring the resistance of a motor, or indeed any resistor (where you make a circuit with voltage and ammeter, draw a graph of V vs. I and use the gradient if Ohmic resistor?

I can't really apply the what you change and measure definition to it... can I?
Changed - setting on power pack (therefore power, and thus voltage and current)
Measured - voltage and current ... to calculate resistance...

Help appreciated, as I have prac test tomorrow.

 

[helper]

In a basic sense:
Independent=Voltage
Dependent=Current

Ensure you turn the circuit off between measurements, so there isn't heating effects.

Be interested in the results for a motor over time as the voltage measure across the motor and current will drop as the motor starts to move.

 

[victorheaven]

so wat r we interested in then? the voltage and current when starting or when the voltage and cureent drop down? help plz

 

[idling fire]

Thanks helper.
We weren't asked about variables for the experiment, so I'll remember for future reference.

All we needed was the resistance while the motor was running (not during startup)... but it was amusing watching the current shoot up and drop down again. Wouldn't like to be trying to identify the max. reading.

 

[alcalder]

When you are finding resistance you want the gradient of your graph V/I = R. Thus I is on horizontal axis and is independent variable and V is the dependent variable on the vertical axis.

However, you are actually changing the voltage out of the power source, so that is really the independent variable.

You are measuring both variables at any rate. Put I on horizontal axis, V on vertical axis and then gradient = R.

 

[Forbidden.]

When you are finding resistance you want the gradient of your graph V/I = R. Thus I is on horizontal axis and is independent variable and V is the dependent variable on the vertical axis.

However, you are actually changing the voltage out of the power source, so that is really the independent variable.

You are measuring both variables at any rate. Put I on horizontal axis, V on vertical axis and then gradient = R.

oh no ....

in my half-yearly i was actually given a question on the pendulum experiment regarding graphic the results then stated that length is an independant variable which was plotted on the y-axis and the period of oscillations was a dependant variable plotted on the x-axis followed by the value of g as a gradient ...

i think i'll lose marks because i stated the wrong variables on the wrong axes.

 

[alcalder]

Fenris,

Don't worry about it too much. When you are graphing things and want the gradient to be the quantity you are looking for then you make the axes what they have to be to make the gradient that thing.

eg v=d/t

Let's say you have a runner who you let run for a certain distance. Then the independent variable is d and you measure t (the dependent variable). BUT if you want to calculate v, then you want t on the x-axis and d on the y-axis even though they are not the independent and dependent variables, respectively. This way v is the gradient.

You could have equally let a runner go for a certain time and then measure the distance. In this case the independent is the time and distance the dependent. It all depends on how you construct the experiment.