electricity Flashcards
what direction do electrons flow
from negative to positive
what is current
rate of flow of charge. made up of electrons
what is potential difference
electrical work done by a power supply per unit of charge flowing in a circuit
what is the relationship between current and potential difference
directly proportional
what is resistance
opposition to the flow of charge
what is the relationship between resistance and current
inversely proportional
what is a zero error
an issue with the set up/ measuring system of practical
in the required practical of resistance in a wire, why does the graph not go exactly through the origin?
other components in circuit have resistance so resistance is never at 0. it is also hard to get crocodile clips exactly at 0cm
what is an ohmic resistor
where resistance remains constant. this causes current to be directly proportional to potential difference
describe the IV graph for a fixed resistor
as potential difference increases, current also increases. directly proportional
describe the IV graph for a filament lamp
as potential difference increases, the current the current starts to increase. gradually current increases less and less each time because the filament in lamp gets hotter increasing resistance
describe and explain the IV graph for a diode
when the diode is connected the right way round then a large current flows as the potential difference increases. if connected the other way round, no current flows as resistance is so high
in a thermistor, what happens to resistance as temperature increases?
decreases
in an LDR, what happens to the resistance as light intensity increases
resistance decreases
what is direct current?
electrons flow in one direction
what is alternating current?
electrons flow in alternating directions
what type of current is the UK’s domestic mains supply?
alternating
what is the potential difference of the UK’s domestic mains?
230V
what is the frequency of the domestic mains supply and what does this mean?
50Hz
the number of times per second the live wire alternates between positive and negative
why do we get electric shocks when we touch live wire?
bodies have 0V of potential difference so if we touch it, there will be a large potential difference across the body so current will flow causing electric shock
what colour is the live wire?
brown
what colour is the neutral wire?
blue
what colour is the earth wire?
green and yellow
what does the earth wire do?
- it is at 0V
- safety device
- if a fault occurs the wire carries current away safely
what is the national grid?
a network of transformers and cables that connects power stations to where power is needed
what does a step up transformer do?
- increases potential difference
- to reduce the current
- reducing energy lost to surroundings as heat
- increasing efficiency of cables
why does the national grid work well below their maximum power output?
there is spare capacity to work with a higher demand
what are conductors?
materials that allow charged particle to flow easily
what are insulators?
materials that don’t allow charged particles to flow easily
what does an electrical wire consist of?
copper core surrounded by plastic/rubber
why do static charges only occur in insulators?
they do not allow the flow of electrons
explain how rubbing an acetate rod with a cloth causes the rod and cloth to become charged
- friction between the rod and cloth
- causes electrons to transfer from rod to cloth
- rod loses electrons and becomes positively charged
- cloth gains to become negatively charged
what conclusion can be drawn from hairs standing on end?
all charges on hair are the same
because they are repelling
explain why a spark jumps between the negatively charged rod and earthed conductor?
- there is a large potential difference between the two objects
- causing electrons to move through the air
- to the conductor to earth the charge
when does an electrical field form?
forms around any object with an electrical charge
which way do field lines point?
away from positive charge, towards negative charge
what shows the strength of an electrical field?
the closer the lines, the stronger
how can charge be transferred in air?
- very large potential difference between two charged objects
- creates a strong electric field between them
- air particles become ionised
- so charge can flow through it it
when does static electricity build up on conductors?
conductor is unable to earth the charge as it does not have contact with the earth and an insulator isolates the charge
what is sparking
as electrical charge builds up on an object, the potential difference between it and earth increases. if the pd is big enough, electrons will jump across the gap. eg lightning
what equation links resistance, current and potential difference
V = I x R
what equation links potential difference, current and power
P = V x I
what equation links power, resistance and current?
P = I^2 x R
what equation links energy transferred, charge flow and potential difference
E = Q x V
static charge can cause a spark and making powder ignite, creating an explosion.
is an explosion more likely to happen when pumping very fine powders or when pumping powers that consist of much larger particles and why? (2)
- very fine powders
- because there is a greater charge build up
how can the risk of exploding due to sparking in a pipe be reduced?
earth the pipes
why would a variable resistor be used in a circuit? (1)
to obtain a range of potential difference values
what material is used in the pin of a plug and why?
brass
because it is hard and a good conductor of electricity
what material is used for the outer case of a plug and why?
plastic
good electrical insulator
which wire inside a plug is the fuse connected to?
live wire
how should multiple solar cells be connected so total resistance is as low as possible? (2)
- in parallel
- because current has more paths to take
why do appliances not switch on when only one switch is closed?
there is a gap in the circuit
what happens to the power output of the power supply in a parallel circuit when two switches are closed at the same time, after one already being closed? (3)
- total resistance of the circuit decreases
- so the current increases
- which increases the power output
what is direct potential difference?
polarity of the potential difference does not change
