Electricity Flashcards
what is double insulation for electrical appliances
if the appliance is made of a plastic casing or the electrics are completely encased in a plastic cover. This means that if a fault develops inside, there is still no route for the current to take to shock you.
(many electrical appliances only have metal casings eg. cookers, washing machines, and fridges)
what is insulation for electrical appliances
the plastic coating covering wires
plastic = insulator so current can’t flow
What is earthing and why is it needed (safety in electric appliances)
when one end of the earth wire is attached to the metal case. This provides a lower resistance route for the current to take, rather than through the user.
Needed if the live wire comes loose and touches the metal case
What is a fuse and how does it work
the fuse consists of a thin wire in a ceramic case
when the current flows through the wire, depending on the limit of the fuse, there will become a point at which, if the current is too high, the fuse wire will heat up and melt. this breaks the circuit and isolates the appliance from the live wire.
How do circuit breakers work and what do they do
they break the circuit (similarly to fuses) using electromagnetics which means they are able to be reset.
what colour is the earth wire and where is it on the plug
green and yellow
in the middle
what colour is the live wire and where is it on the plug
brown
on the right
what colour is the neutral wire and where is it on the plug
blue
on the left
which wire does the fuse sit next to
live wire
why is long cables a hazard of electricity
long cables have larger resistances which means they heat up easier and cause a can fire (resistance is proportional to length of wire)
how does the current in a resistor result in the electrical transfer of energy and an increase in temperature
As current in passed through a wire, the free electrons will collide with the lattice of metal ions (which will be vibrating in place). as they do so they will transfer their energy in the form of heat. if you increase the current, more energy is transferred to the metal ions and the wire heats up more.
equation for Power
Power = current x voltage
equation for energy transferred
energy = power x time
( energy = current x voltage x time)
what is direct current
current (or voltage) that travels in one direction only
what is alternating current
current (or voltage) that changes direction continuously
what kind of current powers the mains supply
Alternating Current
what kind of current does a battery supply
Direct current
4 characteristics of the mains supply
- AC
- not portable
- high voltage
- does not need replacing
4 characteristics of the battery supply
- DC
- portable
- low voltage
- needs replacing/recharging
what is the rule about voltage in a series circuit
voltage is shared across the components SO the total voltage is the sum of the voltages across all the of them
equation linking voltage, current and resistance
voltage = current x resistance
what is the rule about current in a series circuit
the current across each of the components is the same
what is the rule about voltage in a parallel circuit
the voltage across each of the components is the same
what is the rule about current in a parallel circuit
the total current in the main circuit is the sum of the currents in the branches
advantages of using a parallel circuit for a network of lights
- each bulb gets the full battery voltage
- each one can be switched off independently
- if one fails the rest can all still work
what does the graph representing voltage (x axis) vs current (y axis) look like for a filament bulb
on a cross shaped graph:
a shallow bowl shape until the origin the a shallow dome shape after that
what does the graph representing voltage (x axis) vs current (y axis) look like for a diode
on a cross shaped graph:
no current through the minus voltages then after the origin it slopes up slowly
what does the graph representing voltage (x axis) vs current (y axis) look like for a wire
on a cross shaped graph:
straight line through the origin.
- constant gradient
in which direction does current flow in a cell
from the positive terminal to the negative terminal
what is current in terms of particles
the flow of negatively charged electrons
what is potential difference
the amount of energy transferred per unit of charge passing through the terminals (voltage)
what is a volt equivalent to
1 joule per coulomb
what is resistance
the opposition to current
what is the resistance of a good conductor compared to a bad conductor
good conductors - low resistance
bad conductors - high resistance
what is 1 ohm equivalent to
1 volt per ampere
what is the current across a series circuit
the same value at any point
how does increasing the number of components in a series circuit affect the current
it increases the resistance so decreases the current
at a junction in a parallel circuit what happens to current and why
it is conserved (the current going in is the same as the current going out
this is because current is the flow of electrons which are physical matter so can’t be created or destroyed. so when they reach a junction some will go one way and the rest the other
how does current behave across a parallel circuit and why
divides across the branches
depends on what components are causing resistance in that branch
which is the positive and negative end of the cell in a circuit diagram
how does voltage behave in a series circuit
shared between components
how does voltage behave in a parallel circuit
same across all components
advantages of a series circuit
- fewer wires
- all components controlled by single swicth
disadvantages of a series circuit
- the components can’t be controlled separately
- if one component breaks they all stop working
advantages of a parallel circuit
- components can be individually controlled
- if one component breaks the other still work
disadvantages of a parallel circuit
- many wires needed
- all components have the same voltage supply so difficult is components need different voltages
how do you calculate the total combined resistance of resistors in series
add them up
what does the IV graph of a wire look like
what does the IV graph of a fixed resistor look like
what does the IV graph of a filament lamp look like and why
- as current increases the temp of lamp increases
- higher temp causes atoms to vibrate more
- causes an increase in resistance because it is harder for the electrons to flow through
- resistance opposes current so current increases at SLOWER RATE
what does the IV graph of a diode look like
what is the role of a diode
to only allow current to flow in one direction by having a very high resistance in the other direction
in what direction can the current flow when this diode is in the circuit
to the right
what is the symbol of a diode
what is the symbol of a variable resistor
what can be used to indicate the presence of current in a circuit
- lamps and LEDs
what is current
the rate of flow of charge
what is electric current in solid metallic conductors
the flow of negatively charged electrons
why is current conserved at a junction in a circuit
because junctions can’t store current and it can’t just disappear into thin air because charge is conserved. therefore the total amount of current flowing through the circuit must be constant
how does the voltage across two components in parallel compare
it’s the same
what is voltage
the energy transferred per unit charge passed
what are some common hazards of electricity that cause electrocution
Damaged Insulation – if someone touches an exposed piece of wire
Overheating of cables – This could cause a fire or melt the insulation, exposing live wires
Damp conditions – the moisture could conduct electricity either causing a short circuit within a device (which could cause a fire) or posing an electrocution risk
examples of conductors
Silver
Copper
Aluminium
Steel
what is a conductor
a material that allows charge to flow through it easily
examples of insulators
glass, plastic, rubber, air, and wood
practical: investigate how insulating materials can be charged by friction
- rub the ends of the polythene rod with cloth
- without touching the ends, suspend the rod from the stand
- take a (perspex) rod and rub it with another cloth
- bring the two rods together, without touching, and record any observations
- repeat for different materials
- if same repel if opposite attract
what type of materials retain charge
insulators
what is a non contact force
a force that acts on an object without being physically in contact with it
eg electrostatics
uses of electrostatics
inkjet printer
photocopier
insecticide sprayer
how do photocopiers use electrostatic charges
- image of document is projected onto a positively charged copying plate
- plate loses its charge in light areas
- a negatively charged black toner powder is applied to plate (sticks to opposite charge)
- toner transferred onto sheet of paper
- paper is heated so that the powder sticks
what are the two dangers of a spark
- explosion/fire
- electrocution
how can you reduce the dangers of electrostatic charge
earth is by connecting the object to the earth with a conductor
what is the electrostatic danger when refueling vehicles
- fuel is very flammable and runs through pipes at very fast rate
- friction causes charge to build up
- if a spark occurred, explosion
