Determination of Resistivity of a Wire Flashcards

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1
Q

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

A

The resistance of a wire is inversley proportioanl to the cross sectional and so as the area decreases the resistance will increase

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2
Q

How does the resistance of wire change when the length is decreased

A

The resistance of a wire directly proportional to the length of the wire so as the length of the wire decreases its resistance also decreases

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3
Q

What is the Unit of Resistivity

A

Ωm

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4
Q

How do you ascertain the cross sectional area of a thin wire

A
  • Using a micrometer measure the wire’s diameter in at least three different places along the wire
  • Then input the average diameter into the circular area equation
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5
Q

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

A
  • One end of the wire can be fixed and the other end can be connected to the circuit using a crocodile clip
  • The length of conducting wire can be changed by varying the position of the crocodile clip
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6
Q

Why should the power supply be switched off between readings

A
  • The temperature of the wire should remain constant throughout the experiment
  • Switching the power supply off between readings will help ensure this to reduce the effect of heating the wire
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7
Q

Why should the temperature of the wire remain constant throughout this experiment

A

Temperature changes can affect the resistance of the wire

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8
Q

Why does the resiatance of a wire increase when its temperature increases

A
  • As temperature increases the metal ions gain more kinetic energy and so vibrate more
  • These vibrating ions make it harder for charge to pass through the wire and so the wire’s resistance increases
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9
Q

How can the resistivty of a wire be determined from a graph of resiatance against length

A

The gradient of the graph will be R/L so the gradient mutlipled by the cross sectional area will give the resistivity

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10
Q

Why should the current used in this experiment be kept low

A
  • As current increases the temperature of the wire will increases
  • By keeping the current low the heating effect is kept to a minimum
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