Mains/ Static Electricity Flashcards

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1
Q

what is the difference between direct and alternating current?

A

direct current only flows in one direction whereas alternating current regularly changes direction

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2
Q

what type of current is UK mains, what frequency and what voltage?

A
  • alternating current
  • 50Hz
  • 230V
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3
Q

name and describe each wire in a three-core cable connected to mains

A
  • live wire- copper wire coated with brown plastic along which the current enters the device
  • neutral wire- copper wire coated with blue plastic that also connects to the cable in the wall and completes the circuit
  • earth wire- copper wire coated in striped green plastic that provides a path for current to flow from the case of the device to the ground if there is a fault
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4
Q

what is the potential difference between the live wire and earth (0V)?

A

230V

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5
Q

what potential difference are neutral wires and our bodies at?

A

0V, earth potential

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6
Q

why might a live wire be dangerous even when a switch in the mains circuit is open?

A

because any connection between the live wire and earth wire, if a fault occurs in the live wire, the next person to use the appliance could get electrocuted because this would make a complete circuit from your mains supply to the ground (earth) which is prevented by the earth wire

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7
Q

how is the power of a circuit device related to the potential difference across it, the current through it and the energy transferred over a given time?

A

If either p.d. or current increases, the power increases- the rate of energy transfer increases

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8
Q

equations for power=

A
  • P=VI
  • P=I²R
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9
Q

how do appliances transfer energy to the kinetic energy of motors or the thermal energy of heating devices?

A
  • energy is usefully transferred from the chemical store of coal at the power station through an electrical pathway to a kinetic store of the motor
  • energy is usefully transferred from the chemical store of coal at the power station through a heating pathway to a thermal store
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10
Q

equations for energy transferred=

A
  • E= Pt
  • power x time
  • E= QV
  • charge x potential difference
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11
Q

describe the changes in stored energy when domestic electrical appliances are in use

A

electrical energy is converted into thermal energy, which is used to heat or cool the appliance, or into kinetic energy, which powers the movement of the appliance

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12
Q

why is the national grid an effective way to transfer energy?

A
  • as the power transferred must stay the same:
  • step-up transformers are used to increase voltage which decreases current so that less energy is lost through heating the wire and voltage is transported efficiently
  • step-down transformers decrease voltage and increase current to create a save voltage for home use
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13
Q

how is static electricity produced?

A

rubbing insulating surfaces makes them electrically charged because electrons are rubbed off from one of the materials to the other

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14
Q

give evidence that charged objects exert forces of attraction or repulsion on one another when not in contact

A
  • oppositely charged objects attract because their (non-contact) forces act in the same direction, from the positive to the negative charge
  • similarly charged objects’ forces are directed against each other
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15
Q

how are sparks created?

A

the charge difference between the earth and charged surface gets so big and surplus of electrons so large that electrons will jump from the charged surface to the earth, creating a spark

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16
Q

draw electric field patterns for a positive and negative charged sphere

A
  • positive- draw about 8 arrows pointing outwards
  • negative- draw about 8 arrows pointing inwards
17
Q

explain the concept of an electric field and the decrease in its strength as distance from it increases

A
  • an electric field is an area surrounding an electric charge that may influence other charged particles that enter it and they will experience a force
  • the closer to the charged object, the stronger the field and the greater the force experienced by charges in that field