Mains/ Static Electricity Flashcards
what is the difference between direct and alternating current?
direct current only flows in one direction whereas alternating current regularly changes direction
what type of current is UK mains, what frequency and what voltage?
- alternating current
- 50Hz
- 230V
name and describe each wire in a three-core cable connected to mains
- 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
what is the potential difference between the live wire and earth (0V)?
230V
what potential difference are neutral wires and our bodies at?
0V, earth potential
why might a live wire be dangerous even when a switch in the mains circuit is open?
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
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?
If either p.d. or current increases, the power increases- the rate of energy transfer increases
equations for power=
- P=VI
- P=I²R
how do appliances transfer energy to the kinetic energy of motors or the thermal energy of heating devices?
- 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
equations for energy transferred=
- E= Pt
- power x time
- E= QV
- charge x potential difference
describe the changes in stored energy when domestic electrical appliances are in use
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
why is the national grid an effective way to transfer energy?
- 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
how is static electricity produced?
rubbing insulating surfaces makes them electrically charged because electrons are rubbed off from one of the materials to the other
give evidence that charged objects exert forces of attraction or repulsion on one another when not in contact
- 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
how are sparks created?
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
