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Topic 3

Topic 3. Unit 4 - Electricity. Topic 3: Resisting the Movement of Charge. Resistance. Resistance A property of a resistor or load that slows charges. It converts electrical energy into other forms of energy. Good conductors offer little resistance like metal wires.

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Topic 3

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  1. Topic 3 Unit 4 - Electricity

  2. Topic 3:Resisting the Movement of Charge

  3. Resistance • Resistance • A property of a resistor or load that slows charges. • It converts electrical energy into other forms of energy. • Good conductors offer little resistance like metal wires. • A toaster has nichrome wires which offers a lot of resistance creating a lot of heat.

  4. Calculating Resistance: • The unit of resistance is the ohm • The symbol is omega (Ω) • Resistance is measured using an ohmmeter. • The relationship between resistance, voltage, and current is called OHM’s LAW • V = I x R voltage = current x resistance

  5. Problems: • V = I x R • I = V R • R = V I

  6. Try this example: • I = ? • V I = V / R • I = 9 [V] / 18 [Ω] • I = 0.5 [A]

  7. Variable Resistors • Some resistors can vary the amount of resistance they offer resulting in different amounts of energy being released. • Examples: • Dimmer switches • Temperature controls on stoves • Volume controls • Variable speed motors like toy trains

  8. Types of circuit There are two types of electrical circuits: SERIES CIRCUITS PARALLEL CIRCUITS

  9. SERIES CIRCUITS The components are connected end-to-end, one after the other. They make a simple loop for the current to flow round. If one bulb ‘blows’ it breaks the whole circuit and all the bulbs go out.

  10. PARALLEL CIRCUITS The components are connected side by side. The current has a choice of routes. If one bulb ‘blows’ there is still be a complete circuit to the other bulb so it stays alight.

  11. Measuring current This is how we draw an ammeter in a circuit. A A PARALLEL CIRCUIT SERIES CIRCUIT

  12. Measuring current SERIES CIRCUIT 2A • current is the same • at all points in the • circuit. 2A 2A PARALLEL CIRCUIT 2A 2A • current is shared • between the • components 1A 1A

  13. Copy the following circuits and fill in the missing ammeter readings: ? 3A 3A ? 4A ? 1A ? 4A 4A 1A ? 1A

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