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Creating and Selling a Torch Bag

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Background information

When a potential difference is applied across a material that conducts electricity it causes an electrical current in the material. Potential difference is the cause and electric current is the effect. Different currents are caused for a given potential difference depending on the nature of the material, on its shape and on its temperature. As is frequently the case with cause and effects problems, the ratio of the cause to the effect is a useful quantity. Resistance is the name given to the ratio here. Resistance is defined by the following equation:


The resistance of a conductor is the ratio of the potential difference applied across it, to the current passing through it.

The unit of resistance must be the volt per ampere. This is given the name ohm (Ω).

So the unit of resistance is the ohm, symbol Ω. Large resistances are measured is thousands or millions of ohms. So, 1000 Ω = 1kΩ (one kilohm); and 1000000 Ω = 1MΩ (one megohm).

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One wire (1m)Battery pack (1.5v, 3v, and 4.5v)VoltmeterAmmeterTwo clips (one fixed and the other slides along the wireRulerG clapsOptical pins connecting wiresCello type


  1. We will fix the wire in the 1 metre ruler with cello tape.
  2. I will fix the ruler to the table with two “G” claps.
  3. Then we will fix one optical pin in the length of 0cm.
  4. The other one will slide along the wire
  5. We will connect the optical pins into a circuit with voltmeter and ammeter.
  6. I will connect the circuit into a battery pack (1.5v)
  7. I will move the second pin
  8. As I will move it, I will obtain two results, one in the voltmeter and one in the ammeter, for each length between the optical pins
  9. Copy that results
  10. We will change the potential difference. In other words, the voltage will change
  11. Then, with the results, we will calculate the resistance
  12. I will repeat the steps 6, 7 and 8 with different potential differences (1.5v, already done it, 3v and 4.
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This is happened because as we increase the potential difference in the circuit, the wire becomes hotter. In other words, the electrons, which are moving around the circuit pushed by the battery, when they arrive to the resistor they collide with the atoms in the resistor. When the energy given to the atoms is increased, the atoms vibrate faster (and they become hotter), so the resistance increase.


From my point of view, my method was really accurate, because the pin that I used for increase the length, was 1mm wide, what means that gives you an error of 2% in the first length that was 5cm because: 5cm= 50mm, so 50mm/1mm= 2 (this is the percentage of the error) and when we increase the length taken, the error decreases. i.e. 10cm/1mm= 1% of error, and it carries on decreasing. So the precision was very good.

Then the result were very accurate, because I took three different measurements for each length, so the average made a very accurate results.

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This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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