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What factors affect the size of an electric current?

Extracts from this document...

Introduction

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PROJECT QUESTION

What factors affect the size of an electric current?

Electric Current is the flow of charge through all states of matter. There are 5 factors that effects the size of an electric current. They are:

  • Potential Difference between ends (Voltage)
  • Temperature
  • Material of wire
  • Length of wire
  • Area of Cross- section

AIM

To investigate experimentally the effects of conducting wire length on the current.

Figure 1- Circuit Diagram of apparatus used in this investigation

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KEY

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Low voltage variable DC Supply- Power supply by which the voltage

can be varied

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Voltmeter- measure potential difference (voltage) across wire

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Ammeter- measure current

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Varied Conducting Wire length

Constant Conducting Wire lengthimage18.png

SCIENTIFIC THEORY:

An electric current is the flow of electrons around a circuit through a conducting wire of metal. The wire is made up of positive ions, atoms that have lost electrons.

Figure 2- Cross- section of a wire

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When they have enough energy, the electrons in the outer shell of the atoms become free, leaving the atoms as positive ions. They get this energy from the power supply. The sea of free electrons flows past the ions as they gain more energy. However ions are obstacles and they often collide with the electrons, as there is not enough space. Each collision results in a loss of energy. The longer the wire the more atoms it contains.

...read more.

Middle

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The thick membrane stops the negative and positive terminals attracting each other. In the right terminal of the battery the free electrons are repelled because it has a negative charge. The left terminal has a positive charge so it attracts the negative electrons. This gives the electrons in the current a direction to flow in.

PREDICTION:

I predict that the longer the conducting wire length, the smaller the current shall be (lower value in Amps). So if the wire length is doubled then the current shall be halved because the resistance increases (V= I x R)

I = k X1

          L

I α 1

      L

As the wire gets longer (and the temperature remains constant), the resistance shall increase proportionally.

The formula for resistivity is:

R =  pl

         A

R – Resistance

P – Rho- Resistivity of material

L – Length of Wire

A – Area of cross-section

 I  – Current

Using this formula:

When l=1 and A=1, R= p  

So when the length is doubled, the resisitivity is doubled as well:

When l= 2 and A=1, R=2 p.

This suggests that the length is proportional to the resistivity, and the resistance in a circuit is dependant upon the voltage and current

Figure 4- Graph showing that the increase in Current is proportional to the increase in Voltage. This is because the higher the electrical pressure the more electrons go around the circuit. Therefore the line showing resistance is straight and follows Ohms law

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Ohm’s Law:

V = I x R

...read more.

Conclusion

  • A large range of data was collected
  • The surfaces of the contacts were cleaned before they were used so that there was a good connection.
  • Changes made to the method after the preliminary experiment were good, and made a difference as the experiment was a lot fairer and so the results of the main experiment were more accurate than the results of the preliminary work carried out.
  • The crocodile clip was attached to the wire the same way for each of the different wire lengths.
  • As a result of the preliminary we were more familiar with the experiment and so were able to complete the experiment comfortably in the time given without rushing.
  • Constantine wire was used which does not heat up as easily as other wires, and so temperature did not really affect my results

As an extension to this piece of work I could use other wires made from different material like Nichrome wire for example and investigate the pattern between the current and wire length using wires made from different materials. I could also use wires of different thicknesses and investigate how the current changes as the length does.

To further investigate factors that affect the size of an electric current I could look at experimentally, another factor that effects the current and compare my findings to this experiment. I think I would look at the cross-sectional area of the wire. It would provide me with more evidence about changing the size of an electric current.

...read more.

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