Revision topic 16 Flashcards
what are the two wires that are in every main circuit?
live wire and neutral wire
what happens in the mains circuit
the current through main appliance alternate as mains power supply to provide an altering potential difference between these two
what is the neutral wire
it is an earthed wire at the substation
what is the name of the difference between the live wire and the neutral wire
voltage or potential of the live wire
why is the live wire dangerous
because it constantly keeps changing from - to + and back every cycle
what is oscilloscope
it is a device used to find the peak potential difference and frequency of a low voltage a.c supply
the frequency of a.c supply =
1/time taken for 1 cycle
the peak potentail diffrence =
v x Height
why are all mains circuit made of hard-wearing electrical circuits
because the plugs sockets and cables all contain a live wire which is dangerous and can electrocute someone
what are sockets made of
they are made of stiff plastics material with wire inside them, which includes a live wire an earth wire and a neutral wire, all the wires are parallel to each other so if appliances can be turned off without effecting others
what is the earth wire
it is a circuit connected to the ground of your home
what are plugs made off?
stiff plastic material
what is inside the plug
a live pin the earth pin, and the neutral pin stick out through the plug which is all made of copper since it is a good conductor and doest rust, and the wires are sealed and cant touch each other, and the plug contains a fuse between the live pin and the live wire so if too many current passes through it would melt and cut off the life wire
what are cabled used for
they are used for main appliances
what is cables made from
they are made from 2 or 3 insulated copper wires that are surrounded with flexible plastic to protected anyone from receiving an electrical shock when they touch it, the wires are color-coded to distinguish between them
why is copper used in cable
because it is a good conductor of heat and it bends easily
cables of different thicknesses..?
are used in different cases
what does the fuse contain
the fuse contains a thin wire that would heat up and melt if the current is larger than the rating of the fuse
what is the rating of the fuse
it is the maximum amount of current that can pass through the wire without melting it
the fuse is within series with?
the live wire so if the fuse the appliance would then be cut off from the live wire
why is it important to have the right current rating
because if the current rating is too high I wouldn’t fuse when it should do, the heating effect from the large dose of current would cause appliances and cables to catch on fire, in order for the cable to make the heating effect insignificant it needs to be thicker, as the higher the current rating the thicker the cable must be
why is earthing a wire important
to stop it from electrocuting anyone
which one has greater current an earthed heater that touches the frame or an earthed heater that doesn’t touch the frame and why
the earthed heater isn’t touching the frame since it goes through part of the heating element
what is a circuit breaker?
it is an electromagnet in series to a switch that would open when there is too much current passing by once it opens it would stay open unless someone can reset it, this can happen if there is a fault with the appliance that is in series with the circuit breaker.
power =
energy transfer/ time
the rules for any electrical appliance
- the current through it is the charge that flows through it every second
- potential difference across it is the energy transferred to the appliance
- power supply is the energy transferred per second
power supply =
current x potential difference
charge =
current x time
when an electrical appliance is on
electrons would be forced through the appliance by the potential difference of the power supply
what happens when an electrical flow passes through a resistor
the energy would be transferred to a resister making it hotter
the energy transfer in a certain time in the resistor depends on?
the charge passing through it, and the potential difference across it hence:
energy transferred = potential difference x charge
when a charge flows around the circuit at a certain time the energy supplied from the battery would equal
the energy transferred to all components n the circle
for any appliance the energy supplied depend on
- how long it was switched on
2. the power supplied to it
energy transferred (kWh) =
power x time
what is a kilowatt-hour
it is the energy supplied to 1kW in 1 hour
what is the electricity meter
in measures electrical energy we use. and to find the cost of the electrical bill we take the number of kWh used x the cost per kWh
what are precautions you should take for electrical faults
if a fuse blows or a circuit breaker blows when using the main appliance turn it off and don’t use it again unless it’s been checked or if an appliance gets overheated for who smell burning from it again don’t use it until you check it
an electrician selecting a cable for an appliance needs to use
- two-core cable if the appliance is double-insulated and no earth wire is required
- a three-core cable if an earth wire is needed because the case is made of metal
- a cable with conductors of suitable thickness so the heating effect of the current is insignificant
why is filament bulb is very inefficient
because the energy from the hot bulb would gradually make the plastic parts of the bulb brittle and they crack
where are low-energy bulbs more efficient and what are the examples of them
they are more efficient because they dont heat up.
examples:
- CFLs - which are often used for room lighting over filament bulb
- LEDs operate at low voltage and power they are much more efficient than filament and halogen bulb and they last longer
