3.4.8

Resistance

Test yourself

Resistance

If you resist something, you try to fight against it and stop it happening. Resistance happens in electrical circuits when a component resists the flow of current.

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Resistance

  • Most conductors will restrict the flow of current in a circuit.
  • If you want less current to flow, you can increase the resistance.
  • There is more resistance in a wire if:
    • The wire is longer.
    • The wire is thinner.
  • Insulators will have a very high resistance so a current will not flow through them.
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Tasers

  • Some UK Police Officers carry a taser – this is used as a non-lethal method of restraining a violent person.
  • The taser can deliver a potential difference of 50,000 V.
  • However this is not deadly as the high resistance ensures it only delivers a very small current (around 0.002 A), just enough to make the suspects muscles relax.
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Calculation

  • Resistance is measured in ohms.
  • The symbol for ohms is the Greek omega symbol (Ω).
  • Resistance can be calculated using the equation:
    • Resistance (Ω) = potential difference (V) ÷ current (A)
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Ohm's law

  • A resistor is said to follow Ohm's law if:
  • The current that flows through it is directly proportional to the potential difference.
  • This means if you double the potential difference the current will also double.
  • A directly proportional relationship when you draw it on a graph is a straight line through the origin.

Jump to other topics

1Biology

1.1Cells, Tissues & Organs

1.2Reproduction & Variation

1.3Ecological Relationships & Classification

1.4Digestion & Nutrition

1.5Plants & Photosynthesis

1.6Biological Systems & Processes

2Chemistry

2.1Particles

2.2Chemical Reactions

2.3Atoms, Elements, Compounds

2.4The Periodic Table

2.5Materials & the Earth

2.6Reactivity

2.7Energetics

2.8Properties of Materials

3Physics

3.1Energy

3.2Forces & Motion

3.3Waves

3.4Electricity & Magnetism

3.5Matter

3.6Space Physics

4Thinking Scientifically

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