4.3- Electricity

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52 Terms

1
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What is the circuit symbol for an open switch

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2
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What is the circuit symbol for a closed switch

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3
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What is the circuit symbol for a cell

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4
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What is the circuit symbol for a battery

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5
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What is the circuit symbol for a diode

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6
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What is the circuit symbol for a resistor

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7
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What is the circuit symbol for a variable resistor

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8
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What is the circuit symbol for an LED

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What is the circuit symbol for a lamp

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10
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What is the circuit symbol for a fuse

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11
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What is the circuit symbol for a voltmeter

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12
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What is the circuit symbol for an ammeter

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13
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What is the circuit symbol for a thermistor

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What is the circuit symbol for an LDR

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What is needed for a charge to flow in a circuit

A source of potential difference

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What is current

Electric current is a flow of electrical charge. The size of the electric current is the rate of flow of electrical charge

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Equation for charge

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Equation for potential difference

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19
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Define Potential Difference

The differences in charge that drive the movement of charge around (V)

20
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Draw the field lines of a positively charged object

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Draw the field lines of a negatively charged object

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What do closer field lines mean

The electric field is stronger

23
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What is an electric field and how do they interact

  • A charged object creates an electric field around itself.

  • The electric field is strongest close to the charged object.

  • The further away from the charged object, the weaker the field.

  • A second charged object placed in the field experiences a force.

  • The force gets stronger as the distance between the objects decreases.

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Resistance

Anything that slows down charge flow (Ω)

25
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What does current depend on

Resistance of component- more resistance=less current
Potential difference across the circuit- More PD= more current (for fixed resistance)

26
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Draw the IV graph for a ohmic/fixed resistor

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Draw the IV graph for a filament lamp

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Draw the IV graph for a diode

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29
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How do LDRs work

Resistance depends on light intensity
Lower resistance in higher light intensity (BIRD)
Used in automatic night lights (eg switching lights on when it gets dark)

30
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How do thermistors work

Resistance depends on temperature
Lower resistance in higher temperatures (TURD)
Used in thermostats

31
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What are the rules for a series circuit

For components connected in series:

  • there is the same current through each component

  • the total potential difference of the power supply is shared between the components

  • the total resistance of two components is the sum of the resistance of each component.

Rtotal=R1+R2+…

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What are the rules for parallel circuits

For components connected in parallel:

  • the potential difference across each component is the same

  • the total current through the whole circuit is the sum of the currents through the separate components

  • the total resistance of two resistors is less than the resistance of the smallest individual resistor.

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Why does adding another resistor in parallel decrease the total resistance

  • The total potential resistance is the same across each resistor

  • So adding an extra resistor in parallel increases the total current entering the combination

  • Total resistance is equal to the battery potential difference / total current entering the combination

  • So the total resistance is less than before

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Equations for energy

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Equations for power

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What is AC

Alternating current- current that constantly changes direction or polarity and is produced by an alternating voltage. Used in mains supply

Alternating potential difference means voltage changes direction and changes polarity

<p>Alternating current- current that constantly changes direction or polarity and is produced by an alternating voltage. Used in mains supply</p><p>Alternating potential difference means voltage changes direction and changes polarity</p>
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What is DC

Direct Current- Current that always flows in the same direction or polarity and is produced by a direct voltage.
Supplied by batteries

Direct potential difference means the voltage stays in the same direction, and keeps the same polarity

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Frequency of uk mains supply

50Hz

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Potential difference of uk mains supply

230V

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Is the uk mains supply AC or DC

AC

41
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Why are the wires in a plug colour labelled

The insulation covering each wire is colour coded for easy identification

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Colour, PD and purpose of live wire

- Brown
- 230V
- Provides alternating potential difference from mains supply

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Colour, PD, and purpose of neutral wire

- Blue
- About 0V
- Completes the circuit- carries electrons back to the power source

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Colour, PD, and purpose of earth wire

  • Yellow and green striped

  • 0V

  • Stops appliance casing becoming live; Current only flows through the earth wire when there's a fault

45
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Draw a diagram of a plug from the back

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What is the purpose of electrical appliances

Everyday electrical appliances are designed to bring about energy transfers.

The amount of energy an appliance transfers depends on how long the appliance is switched on for and the power of the appliance.

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Describe how electric shocks work

Your body has a potential difference of 0V, the wire has a PD of 230V
There is potential difference between the body and the wire
Your body provides a route to the earth
This causes current to flow through your body- can cause injury or even death

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What is the national grid

The National Grid is a system of cables and transformers linking power stations to consumers.

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Describe the stages in the national grid

- Power station produces electricity by burning fuel to heat water, which produces steam, which spins a turbine, and runs a generator, which converts kinetic energy to electrical energy
- A step up transformer increases the potential difference, and therefore decreases current
- This is because P lost=I2R, so less current= less power lost=more efficient; more current would heat up the wire, which would lose energy through thermal energy dissipation
- At this point, PD is about 400,000V in the power lines and pylons
- When it reaches houses, a step-down transformer decreases the PD to 230V for domestic use

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How are static charges created

  • When certain insulating materials are rubbed against each other they become electrically charged.

  • Negatively charged electrons are rubbed off one material and on to the other.

  • The material that gains electrons becomes negatively charged.

  • The material that loses electrons is left with an equal positive charge.

  • This causes equal opposite charges between the objects

  • There is attraction between the objects

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What is an electric spark

The passage of electrons across a gap between a charged object and the earth, or an earthed conductor.
This usually happens when the gap is small

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What are the steps to an electric spark

  1. Electric charge builds on an object

  2. Potential difference between object and earth (at 0V) increases

  3. When the potential difference is large enough there is a spark

  4. The charge has been earthed