PAG 3.1 - Determination of Resistivity

Question 1

Equation used to calculate the resistivity of a wire

Answer 1

resistance x area / length

Question 2

How does the resistance of a wire change when the cross-sectional area decreases?

Answer 2

Resistance is inversely proportional to the cross-sectional area, area decreases and resistance increases

Question 3

How does the resistance of the wire change when the length decreases?

Answer 3

Resistance of a wire directly proportional to the length of the wire, so as the length decreases, the resistance also decreases

Question 4

How does the resistivity of a wire change if the resistance is increased?

Answer 4

Resistivity of a wire is directly proportional to the resistance, so as the resistivity increases, resistance increases

Question 5

What is the unit of resistivity?

Answer 5

ohm meter

Question 6

Suggest how the length of conducting wire can be varied when carrying out this experiment

Answer 6

One end of the wire can be fixed and the other end connected to the circuit using a crocodile clip. The length of the conducting wire can be changed by varying the position of the crocodile clip

Question 6

How do you measure the cross-sectional area of a thin wire?

Answer 6

Using a micrometer in at least 3 different places, average diameter used in circle equation

Question 7

Describe how the length of the wire should be measured

Answer 7

Length measured using a meter ruler, with wire held taught.

Question 8

What device is used to measure the potential difference across the wire, and how is it connected?

Answer 8

voltmeter in parralel

Question 9

Why should the power supply be switch off between readings?

Answer 9

Temperature of the wire should remain constant throughout the experiment. Switching the power supply off between readings will reduce the heating of the wire

Question 10

Why should the temperature of the wire remains constant throughout this experiment?

Answer 10

Temperature changes can affect the resistance of the wire. In this experiment, temperature is a control variable

Question 11

Why does the resistance of a wire increases when its temperature increases?

Answer 11

As the temperature increases, the metal ions gain more kinetic energy and vibrate more, making it harder for charge to pass through the wire, so resistance increases

Question 12

How can the resistivity of a wire be determined from a graph of resistance against length?

Answer 12

Gradient will be R/L and multiplying the gradient by the cross-sectional area

Question 13

Why should the current used in this experiment be kept low?

Answer 13

As the current increases, the temperature of the wire will increase, by keeping the current low, the heating effect should be to the minimum

Question 14

Suggest how you could ensure that your length measurements are taken from the same position each time

Answer 14

Meter ruler taped in place below the wire

Question 15

What factors lead to uncertainties in this experiment?

Answer 15

Resistance between the crocodile clips and wire as well as the contact of the leads and the power supply. There may also be a zero error due to the positioning of the ruler and crocodile clip at the zero end.

Question 16

What device could replace the voltmeter and ammeter in this experiment?

Answer 16

Instead of a voltmeter and ammeter, a multimeter could be used to measure the current and potential difference. However, may lead to lower resolution of data.

Question 17

Does the resistivity of a material change depending on the dimensions?

Answer 17

Resistivity is a material property and so is fixed for a given material, regardless of dimension

Question 18

How can the percentage difference in your experimental value and accepted value be calculated?

Answer 18

Your value - accepted value/ accepted x 100