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Resistance Exam Question!

Scapepicture

A cell is in series with two boxes, P and Q.

•

Each box contains two resistors in parallel.

•

One of the four resistors has a value of 1 Ohm.

•

Each of the other resistors has a value much greater than 1 Ohm

a) State what measurements the student, with the aid of a voltmeter, must take in order to determine which box contains the 1.0 Ohm resistor.

b)Explain how the measurements you describe would enable the student to make the correct identification of the box with the 1 Ohm resistor.

OUCH!

Reply 1

watchthis

Original post by Scapepicture

A cell is in series with two boxes, P and Q.

•

Each box contains two resistors in parallel.

•

One of the four resistors has a value of 1 Ohm.

•

Each of the other resistors has a value much greater than 1 Ohm

Well, for (a);
You would obviously need to have an ammeter connected in series as well.
You would need to take measurements of varying potential difference and the current corresponding to each p.d, because that is what you need to calculate the resistance using R=V/I

for (b);
Most questions like this would want you to plot a graph, so plot a graph of current against p.d, and then find the gradient which would probably be a straight line assuming the practical was done properly.

The gradient of the graph would represent the resistance;
and presumably you would know the formula for resistors in parallel would be;
R= 1/R1 + 1/R2 and etc.
As you know one of the resistors is a 1 ohm resistor, the formula would change into,

R= 1 + 1/R2

And you could probably find the box which contains the 1 ohm resistor using this method.

Hope I helped :smile:

Reply 2

Stonebridge

Original post by Scapepicture

A cell is in series with two boxes, P and Q.

•

Each box contains two resistors in parallel.

•

One of the four resistors has a value of 1 Ohm.

•

Each of the other resistors has a value much greater than 1 Ohm

The box with the 1 ohm and the large resistor in will have a total resistance of very nearly one ohm.
The other box will have a resistance which is much higher.
For example, if it was two 100 ohm resistors it would be 50 ohms.
You just need to find out which box has the higher resistance. V=IR should do the trick.