Electricity Flashcards
electric current definition
the rate of flow charge
direction of current flows from..
the positive terminal to the negative terminal
link the equation involving, charge, current and time
Charge (C)= Current (A) x Time (s)
how do you meassure current
ammeter
how to connect ammeter
in series so all the charge flows through it
potential difference definition
the amount of energy transferred per unit of charge passing through the terminals
1 volt is equal to __
one joule
potential difference equation
V = energy transferred/ charge moved
how is potential difference measured
voltmeter
how are voltmeters connected
in parallel
why do voltmeters have to be connected in 2 points of circuit
as it needs to calculate the difference
resistance
opposition to current
the higher the resistance =?
the lower the current
do good conductors have low or high resistance
low
symbol for resistance
R
how is resistance measured
ohms (one volt per ampere)
equation linking voltage, current and resistance
potential difference= current x resistance
how is current in a series circuit
the same value at any point
what does the amount of curent flowing in a series circuit depend on
- voltage
- number of components in circuit
increasing voltage=
increase in current
what happens in a juction where 2 or more wires meet
the current is always split at a circuit junction
is current and charge conserved
yes
voltage in a series circuit
shared between the components
- the voltage across components is the same
advantages of series circuit
- all components are controlled by a single switch
- fewer wires are required
disadvantages of series circuit
- components cannot be controlled separately
- if one component breaks they all stop working
what does a parallel circuit consist of
2 or more components attached across different branches of the circuit,
advantages of parallel circuis
- invidually controlled
- even if one breaks, others function
disadvantages of parallel circuits
- more wires involved
- all components have the same v supply, so harder to control.
resistors in series
the total resistance is equal to the sum of their individual resistance
potential difference and current are ————
porportional
current through a fixed resistor
increases as the potential difference increases
filament lamp, current and voltage relationship
not directly proportional
why is the relationship in a filament lamp,current and voltage not directly proportional
resistance of a filament lamp increases as the temperature of the filament increases
diodes- foward bias
allow current to flow in one direciton only
diode - reverse bias
the diode has high resistance so no current flows
2 types of resistors
- fixed resistor
- variable resistor
fixed resistors
resistance that remains constant
variable resistors
can change the resistance by changing the length of the wire that makes up the circuit .
thermistors
temperature-dependent resistor
- higher temp= resistance decreases
LDRs
more light intensity= resistance of LDR decreases
lamps
illuminate when a current flows in a circuit
LEDs
types od diodes, only lights up if the current passes in that direction
power
the rate of energy transfer per second
power equation
power (W) = current x voltage
fuse
cuts off the flow of electricity to an appliance if the current becomes too large
what happens to a fuse if the current is too large
wife heats up and melts, causes wire to break and stop the circuit
work
when charge flows through a circuit
work done
equal to energy transferred
what does the amount of energy transferred by electrical work in a component depend on
- current
- voltage
- amount of time
energy transferred equation
E= P (w) x t
common hazards in electricity
- damaged insulation
- overheating of cables
- damp conditions
safety features which are built into domestic appliances
- double insulation
- earthing
- fuses
- circuit breakers
double insultation
- insulation around the wires themselves
- a non metallic case that acts as a second layer of insulation
earthing
- provides a low resistance path to the ground
- no resistance a large current can flow
what occurs if there is a malfunction in current
- earth wire provides a low resistance path to the groudn
- it casegrounds a surge of current in the earth wire and live wire
- high current through the fuse causes it to melt and break
- cuts off the supply of electricity.
what do fuses consist of
glass cylinder containing a thin metal wire
circuit breaker
automatic electromagnet switch that breaks circuit if the current exceeds a certain value
advantage of circuit breaker
- doesn’t melt so it can be reset and used again
- works much faster
what happens when electricity passes through a component
some of the energy is transferred to heat, increasing the temp
why is energy transferred
as a result of collisions between
- electrons flowing in a conductor
- lattice of atoms within the conductor
direct current
- current that is steady, and constantly flowing in same direction in a circuit from + to -
what produces a direct current
electrical cells or batteries
alternating current
- current that continuously changes its direction going back and forth aroud a circuit
frequency of an alternating current
number of times the current changes direction in a second
conductor
material that allows charge to flow through it easily
conductor examples
steel, copper, aluminum, silver
what are conductors made up of on the atomic scale
positively charged metal ions with their outermost electrons delocalized.
insulator
material that has no free charges so it does not allow the flow of charge through them very easily
insulator examples
rubber, plastic, glass
what type of electricity do insulators conduct
static electricity.
charging by friction
when insulating materials are rubbed against one another, they become electrically charged
rubbing a polythene rod and cloth together
- electrons transfer from the cloth to the rod, so the rod gains electrons,
- the cloth is then positively charged
attraction of atoms
positive and negative
repulsion of atoms
negative and negative
positive and positive
uses of static electricity
photocopiers
insecticise sprays
what is the danger of static electricity
sparking, risk of electrocution.
how do you prevent the risk of sparking
earthing
