Using the gradient for a calculation (1 Viewer)

[Michaelmoo]

So I'm not really good at the using the gradient to find a value thing. Thort I did it right in the exam, but ended up getting it wrong..

For example, for a graph of Force (vertical axis) verses length of wire (horizontal axis); where a certain length of wire was placed in a magnetic field at right angles. How would you use the gradient to find the value of B? Given that:

I = 2.5A
Gradient = 10Nm

One point on the graph corresponds to a force of 5N and a length of wire of 0.05m.<!-- google_ad_section_end --></SPAN>

 

[helper]

As soon as you say one point, I wonder if you are using the slope. Here a two systems to follow

Write Equation that describes the relationship
F=BIl
Write it in form of y=mx + b

In your case y= F, x=l

F= BI x l + 0
so slope m=BI
Calculate slope using rise/run and substitute in for m and I to calculate B

OR


F=BIl
So
So calculate slope using rise/run and subsititute

 

[Michaelmoo]

No. I did use the gradient, the point in there was just to let you get a feel of the gradient.

I actually used your second method. I substituted the gradient into F/L. The only exception though was I didn't write in the word "slope" or "gradient". I just subd it in.

Guess I should of made it clearer.

Thanks.

 

[helper]

You should clearly show the slope calculation, using two points, and clearly state you are equating the slope to the equation.

Even if the line is going through 0,0 or is supposed to, make sure you are choosing points of the line. Eg. Slope =

Make sure the points you choose to use are read of the graph and not taken from the data table. Even better if you mark onto the graph the triangle you are using to work out the slope.

If drawing the line of best fit, don't assume that if the equation should go through 0,0 that it will because if there is a systematic error, the shift in the zero point is where the error shows up.

 

[Michaelmoo]

If drawing the line of best fit, don't assume that if the equation should go through 0,0 that it will because if there is a systematic error, the shift in the zero point is where the error shows up.

What about if you are working with something obvious. For example V against I, and one of the data points is 0,0. Then do u pass the line of best fit through 0,0?

 

[helper]

Not if it isn't a measured data point because there may be an error in the zero measurment. Like when a voltmeter doesn't return to zero exactly each time.